02 18 2014 IChO46 Preparatory Problems

8/12/2019 02 18 2014 IChO46 Preparatory Problems

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Preparatory Problems

46thInternational Chemistry Olympiad (IChO - 2014)

Editorial Board

Nguyen Tien Thao, Editor in Chief

Nguyen Minh Hai

Nguyen Van Noi

Truong Thanh Tu

Hanoi University of Science, Vietnam National University, Hanoi

Tel: 00! !"#!0$%#%& 'a(: 00! !"#!0$%#% Email: icho)0%!*re*+huseduvn

Febrary 1!th" 2014 (#e$ised)


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46thInternational Chemistry Olympiad Preparatory Problems

%anoi" &ietnam - 2014

Contributing AuthorsLe Minh Cam, Hanoi National University of Education

Vu Viet Cuong, Hanoi University of Science, VNU-Hanoi

Pham he Chinh, !nstitute of Chemistry, V"S

Nguyen Huu #inh, Hanoi National University of Education

ran hi #a, Hanoi National University of Education

Nguyen Van #au, Hanoi University of Science, VNU-Hanoi

#ao Phuong #ie$, Hanoi National University of Education

Pham Huu #ien, Hanoi National University of EducationNguyen Hien, Hanoi National University of Education

Hoang Van Hung, Hanoi National University of Education

Nguyen Hung Huy, Hanoi University of Science, VNU-Hanoi

u Vong Nghi, Hanoi University of Science, VNU-Hanoi

rieu hi Nguyet, Hanoi University of Science, VNU-Hanoi

#o %uy Son, Vietnam "tomic Energy !nstitute

a hi hao, Hanoi University of Science, VNU-Hanoi

Nguyen ien hao, Hanoi University of Science, VNU-Hanoi

Lam Ngoc hiem, Hanoi University of Science, VNU-Hanoi

Ngo hi huan, Hanoi University of Science, VNU-Hanoi

Vu %uoc rung, Hanoi National University of Education

#ao Huu Vinh, Hanoi University of Science, VNU-Hanoi

Acknowledgements

&e 'ould li(e to e)$ress our dee$ gratitude to the mem*ers of the !nternational Steering

Committee for their valua*le comments and suggestions and to #r+ Vu Viet Cuong, #r+ NguyenHung Huy, and #r+ Pham Van Phong for their (ind colla*orations+

Sincerely yours,

Editors

Chemistry The flavor of life )


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%anoi" &ietnam - 2014PrefaceWe are happy to provide Preparatory Problems for the 46

th

International ChemistryOlympiad. These problems were prepared with reliance on fundamental topics firmly

covered in high school chemistry courses along with some advanced topics for the

chemistry olympiad competition. These topics are listed under Topics of Advanced

Difficulty, and their applications are given in the problems. Solutions will be sent to

Head Mentors on February 20th, 2014 and updated on '''iho2014hsed$non

May 31st, 2014. Although a lot of efforts have gone to making this Booklet, some

mistakes, typos may still be there. We welcome any comments, corrections, or questions

about the problems to iho2014prep*hsed$n

We hope that these problems will be motivating for students to participate in the

IChO-2014 competition. We believe that IChO-2014 will not only be a chemistry

competition, but also a pleasant time for you to know about Vietnamese culture.

-e look forward to seeing you in Hanoi and at Hanoi University of Science, Vietnam

National University in Hanoi.

Hanoi, January 31st, 2014

Editor in Chief

Nguyen Tien Thao

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, "
http://www.icho2014.hus.edu.vn/mailto:[email protected]://www.icho2014.hus.edu.vn/mailto:[email protected]


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February 18th, 2014 (Revised)

Contents

Fields of Advanced Difficulty 6

Physical Constants, Symbols and Conversion Factors 7

Part 1. Theoretical Problems 8

Pro*lem + Polar and non-$olar molecules

Pro*lem .+ Calculations of lattice energy of ionic com$ounds /

Pro*lem 0+ " frog in a &ell .

Pro*lem 1+ Electrons in a .,0-#imensional 2o) 1

Pro*lem 3+ ug of 'ar 4

Pro*lem 4+ 5adiochemistry 6

Pro*lem 6+ "$$lied thermodynamics 7

Pro*lem + Com$le) com$ounds ./

Pro*lem 7+ Lead com$ounds .1

Pro*lem /+ "$$lied electrochemistry .4

Pro*lem + Phos$horic acid .6

Pro*lem .+ 8inetic chemistry .

Pro*lem 0+ 8inetics of the decom$osition of hydrogen $ero)ide 0/

Pro*lem 1+ Magnetism of transition metal com$le)es 0

Pro*lem 3+ Structure and synthesis of "l-8eggin ion 01

Pro*lem 4+ Safrole 03

Pro*lem 6+ !mida9ole 0

Pro*lem + Small heterocycles 07

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Pro*lem 7+ Vitamin H 1

Pro*lem ./+ No $erfume 'ithout :asmine 11

Pro*lem .+Vietnamese cinnamon 16

Pro*lem ..+ Cinnamic acid 17

Pro*lem .0+ ris;trimethylsilyl


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ields o! Ad"anced #i!!icult$

+heoretial

Kinetics: .ntegrated first3 and second3order rate e4uation& analysis of moderatelycom*le( reactions mechanisms using the steady state a**ro(imation, the use of the5rrhenius e4uation

Thermodynamics: Electrochemical cells, the relationshi* 1et6een e4uili1riumconstants, electromotive force and standard 7i11s energy, the variation of thee4uili1rium constant 6ith tem*erature

Quantum mechanics: article3in3a31o( calculations, or1ital3overla*s, s*in3or1itcou*ling

Sectroscoy! .nter*retation of .8 s*ectra and relatively sim*le %H, %"C, and )95lNM8 s*ectra: chemical shifts, multi*licities, cou*ling constants and integrals

"dvanced #nor$anic!Trans effect& the use of sim*le crystal field theory to e(*lainelectronic configurations in octahedral and tetrahedral com*le(es& calculation ofthe magnetic moment using the s*in3only formula, solid state structures, *acing

arrangement

"dvanced %r$anic! Stereoselective transformations& aromatic nucleo*hilicsu1stitution& *olycyclic aromatic com*ounds and heterocycles

Chemistry The flavor of life $


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Pratial

&asic synthesis techni'ues: Thin layer chromatogra*hy, E(traction, 'iltration,;rying, Titration

* is sectroscoy+

Physial Constants" ,ymbols and Con$ersion Fators

5vogadro%0)"mol?%

@oltAmann constant, -@= %"09>%0?)"

2B?%

Universal gas constant,R . "%!# 2B?%Bmol?% 00)0# atmBDB?%Bmol?%

S*eed of light, c . )9>%0mBs?%

lanc%0?"!2Bs

'araday constant,F = $!#"">%0!C

Mass of electron, me= %0")%#>%0?"%gBmol3%

Standard *ressure,/= % 1ar = %0#a

5tmos*heric *ressure,/atm= %0%")#>%0#a = 9$0 mm Hg = 9$0 Torr

Fero of the Celsius scale, )9"%# % *icometer Gm = %0?%)m& %I = %03%0m& nanometer Gnm . %0?m

% eV = %$ > %03%2

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Periodi +able o. Elements 'ith #elati$e /tomi asses

118

1H

1.008 2 13 14 15 16 17

2He

4.003

3Li

6.941

4Be

9.012

5B

10.81

6C

12.01

7N

14.01

8O

16.00

9F

19.00

10Ne

20.18

11Na

22.99

12Mg

24.31 3 4 5 6 7 8 9 10 11 12

13Al

26.98

14Si

28.09

15P

30.97

16S

32.07

17Cl

35.45

18Ar

39.95

19K

39.10

20Ca

40.08

21Sc

44.96

22Ti

47.87

23

50.94

24Cr

52.00

25M!

54.94

26Fe

55.85

27C"

58.93

28Ni

58.69

29C#

63.55

30$!

65.38

31%a

69.72

32%e

72.64

33A&

74.92

34Se

78.96

35Br

79.90

36Kr

83.80

37'(

85.47

38Sr

87.62

39)

88.91

40$r

91.22

41N(

92.91

42M"

95.96

43Tc

*98+

44'#

101.07

45',

102.91

46P-

106.42

47Ag

107.87

48C-

112.41

49!

114.82

50S!

118.71

51S(

121.76

52Te

127.60

53

126.90

54/e

131.29

55C&

132.91

56Ba

137.33

57La

138.91

72H

178.49

73Ta

180.95

74

183.84

75'e

186.21

76O&

190.23

77r

192.22

78P

195.08

79A#

196.97

80Hg

200.59

81Tl

204.38

82P(

207.2

83Bi

208.98

84P"

209

85A

210

86'!

222

87

Fr223

88

'a226.0

89

Ac227

104

'261

105

Ha262

58Ce

140.12

59Pr

140.91

60N-

144.24

61P

145

62S

150.36

63#

151.96

64%-

157.25

65T(

158.93

66

162.50

67H"

164.93

68r

167.26

69T

168.93

70)(

173.05

71L#

174.97

90T,

232.04

91Pa

231.04

92

238.03

93N:

237.05

94P#

244

95A

243

96C

247

97B;

247

98C

251

99&

254

100F

257

101M-

256

102N"

254

103Lr

257

PA%T 1. T&'(%'T)CA* P%(+*',-

Problem 1. Polar and non-polar molecules

.n chemistry, a molecule is considered nonoar 6hen its *ositive charge

center and negative charge center coincide, ie the charge distri1ution is

symmetrical in the molecule /n the other hand, 6hen a molecule has t6o distinct

centers for *ositive and negative charges, it is consideredoar

This charge distri1ution *ro*erty is measured 1y a 4uantity called the dioe

moment 6hich is defined as the magnitude of the charge 4 and the distance

1et6een the charges:

1'=

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The di*ole moment is a vector *ointing from the *ositive charge center to the

negative one

The di*ole moment is often e(*ressed in de1yes G; The relationshi* 1et6een

de1yes G; and coulom1 meters GCBm in S. units is as follo6s: % ; = """>%0?"0

CBm

1 The di*ole moment is closely related to the molecular geometry .n order to

calculate the net di*ole moment of multi3atomic molecules, 6e can add thedi*ole moment vectors for individual 1onds .n this case, an individual 1ond is

considered to have its o6n di*ole moment called the 1ond moment

'or a non3linear molecule 6ith three atoms, 5@C, the net di*ole moment can 1e

calculated 1y adding vectors in 6hich %and ) are the 1ond moments for 5@ and

5C 1onds, and is the 1ond angle ;etermine the general e4uation for calculating

the net di*ole moment

2 The directions of the individual 1ond moments should 1e considered

)% The molecule of C/) is linear Calculate the net di*ole moment of the

molecule

)) 5 non3linear molecule of 5)@ such as H)S has the net di*ole moment 0

;etermine for H)S if SH= )$%>%0?"0CBm and the 1ond angle = )0o

The 1ond angle HCH in the formaldehyde molecule is determined

e(*erimentally to 1e a**ro(imately %)0o& the 1ond moments for C3H and C3/

1onds are HCJ = 0! ; and /CJ = = )" ;, res*ectively

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"% ;etermine the or1ital hy1ridiAation of C and / atoms, and *lot the

overla*s of or1itals in the formaldehyde molecule

") Calculate the net di*ole moment GJ of the formaldehyde G;, given the order

of the electronegativity as HC/ KKK >> Gints! 3ectrone$ativity is the abiity

o an atom in a moecue to attract shared eectrons to itse

4The di*ole moments of 6ater and dimethylether in gaseous state are determined

as %! ;, and %) ;, res*ectively The 1ond angle formed 1y t6o 1ond moments

of /3H in the 6ater molecule is %0#o The 1ond angle formed 1y t6o 1ond

moments of /3C in the ether molecule is %%0o

Estimate the 1ond angle formed 1y the 1ond moments of /3H and C3/ in the

methanol molecule, given that the di*ole moment of methanol molecule is %$ ;

5ssume that individual 1ond moments are unchanged in different molecules

Problem 2. Calculations of lattice energy of ionic compounds

1Dithium is the lightest metal and does not e(ist in *ure form in nature due to its

high reactivity to 6ater, moisture, o(ygen Dithium readily forms ion 6ith a %L

charge 6hen reacting 6ith nonmetals -rite do6n the follo6ing chemical

reactions at room tem*erature:

%% Dithium reacts 6ith 6ater

%) Dithium reacts 6ith halogens, eg Cl)

%" Dithium reacts 6ith dilute sulfuric acid and concentrated sulfuric acid

2The change in enthal*y of a *articular reaction is the same 6hether it taes *lace

in one ste* or in a series of ste*s GHesss la6 Use the follo6ing data:

Su1limation enthal*y of DiGs, SH = %# 2Bmol?%

.oniAation energy of DiGg, . = #!0 eV

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;issociation enthal*y of Cl), ;H = )!) 2Bmol?%

Electron affinity of ClGg, E = 3"! eV

'ormation enthal*y of DiClGs, fH = ? !0)" 2Bmol?%

$),0=+5ir I& ",%=61r I& N5= $0)>%0)"mol?%

)% Esta1lish the @orn3Ha1er cycle for lithium chloride crystal

)) Calculate the lattice energy UoG2Bmol3% using the @orn3Ha1er cycle

.n *ractice, e(*erimental data may 1e em*loyed to calculate lattice energies in

addition to the @orn3Ha1er cycle /ne of the semi em*irical formulae to calculate

the lattice energy Uofor an ionic com*ound, 6hich 6as *ro*osed 1y a*ustinsii,

is as follo6s:

U0 = 3 )9)+

+

+

rr

ZZ

+

+ rr

"!#,0%

6here: is the num1er of ions in the em*irical formula of ionic com*ound,

rLand r3are the radii of the cation and anion, res*ectively, in I,

FLand F3are cation and anion charges, res*ectively,

U0is the lattice energy, in calBmol3%

Use the a*ustinsii em*irical formula to calculate UoGin 2Bmol?%

of DiCl crystal,

given that % cal = !%! 2

4 @ased on the results of t6o calculation methods in sections ) and ", choose the

a**ro*riate 1o(:

5ccording to the @orn3Ha1er cycle and a*ustinsii em*irical formula

for lithium chloride crystal structure, 1oth methods are close to the

e(*erimental value

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, %%


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/nly the calculated result of the @orn3Ha1er cycle is close to the

e(*erimental value

/nly the calculated result of the a*ustinsii em*irical formula is close

to the e(*erimental value

7ata: 7iven the e(*erimental value of lattice energy for DiCl is !0! 2Omol

.n the formation of DiCl crystal, it is found out that the radius of lithium cation is

smaller than that of chloride anion Thus, the lithium ions 6ill occu*y the

octahedral holes among si( surrounding chloride ions 5dditionally, the 1ody edge

length of DiCl cu1ic unit cells is #%! I 5ssume that DiL ions Pust fit into

octahedral holes of the closest *aced chloride anions

#% Calculate the ionic radii for the DiLand Cl

3ions

#) Com*are the calculated Gtheoretical radii 6ith the e(*erimental radii given

1elo6, and choose the a**ro*riate 1o(:

@oth calculated radii of lithium and chloride ions are close to the

e(*erimental values

/nly the calculated radius of lithium ion is close to the e(*erimental value

/nly the calculated radius of chloride ion is close to the e(*erimental value

The e(*erimental radii of DiLand Cl

?are 0$) I and %" I, res*ectively

Problem 3. A frog in a well

The energy levels of an electron in a one3dimensional 1o( are given 1y:

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%anoi" &ietnam - 2014)

)

n )

hE n

mD= n: %, ), "Q

in 6hich h is the lancs constant, mis the mass of the electron, and D is the

length of the 1o(

1 The electrons in a linear conPugated neutral molecule are treated as

individual *articles in a one3dimensional 1o( 5ssume that the electrons are

delocaliAed in the molecular length 6ith the total num1er of N electrons and

their arrangement is governed 1y the *rinci*les of 4uantum mechanics

%% ;erive the general e(*ression for EDUM/ ? H/M/ 6hen an electron is e(cited

from the H/M/ to the DUM/

%) ;etermine the 6avelength of the a1sor*tion from the H/M/ to the DUM/

2 5**ly the model of electrons in a one3dimensional 1o( for three dye

molecules 6ith the follo6ing structures Gsee the structural formula 5ssume

that the electrons are delocaliAed in the s*ace 1et6een the t6o *henyl grou*s

6ith the length D is a**ro(imately e4ual to G) L %G0%!0 nm, in 6hich is

the num1er of the dou1le 1onds

a %,!3di*henyl3%,"31utadiene

Gdenoted as B3

1 %,$3di*henyl3%,",#3he(atriene

Gdenoted as %+

c %,3di*henyl3%,",#,93octatetraene

Gdenoted as O+

)% Calculate the 1o( length D GI for each of the dyes

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)) ;etermine the 6avelength Gnm of the a1sor*tion for the molecules

of the investigated dyes

8ecalculate the 1o( length D GI for the three dye molecules, assuming that the

electrons are delocaliAed over the linear conPugated chain 6hich is *resented

as a line *lotted 1et6een the t6o *henyl grou*s Gsee the structural formula

The 1ond angle C ? C ? C is %)0 o and the average length of C ? C 1ond is 0%!0

nm

4 7ive the follo6ing e(*erimental data on the 6avelength of a1sor*tion

!% ;etermine the 1o( length D GI of the linear conPugated chain for each of the

three investigated dyes

!) Ta1ulate the values of the 1o( length D for the dyes calculated a1ove 1y thethree different methods, denoted as 1, 2, and Choose the method 6hich is the

most fit to the e(*erimental data

Problem 4. Particles in 2, 3 - Dimensional o!

1 .n ro1lem ", the energy E of *article in one3 dimensional 1o( is calculated as:)

)

)

hE =n

mD

6here his lancs constant& mis the mass of the *article& D is the 1o( length&

nis the 4uantum num1er, n= %, ), "Q

Chemistry The flavor of life

Su1stance B3 %+ O+Gnm ")# "#0 #$%

%!


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5n electron in a %0 nm one3dimensional 1o( is e(cited from the ground state to a

higher energy level 1y a1sor1ing a *hoton of the electromagnetic radiation 6ith a

6avelength of %"9!>%03#m

%% -hat is the energy ga* GE of the t6o mentioned transitionsR

%) ;etermine the final energy state for this transition

2 The treatment of a *article in a one3 dimensional 1o( can 1e e(tended to a t6o3

dimensional 1o( of dimensions D( and Dyyielding the follo6ing e(*ression for

energy:

)))

y() )

( y

nnhE =

m D D

+

The t6o 4uantum num1ers inde*endently can assume only integer values

Consider an electron confined in a t6o3dimensional 1o( that is D (= 00 nm in the

( direction and Dy= #00 nm in the y direction

)% -hat are the 4uantum num1ers for the first three allo6ed energy levelsR -rite

the first three energy, E(y, in order of increasing energyR

)) Calculate the 6avelength of light necessary to move an electron from the firste(cited state to the second e(cited one

Similarly, the treatment of a *article in a one3dimensional 1o( can 1e e(tended

to a rectangular 1o( of dimensions D(, Dy,and DA, yielding the follo6ing e(*ression

for energy:

)) ))

y( A) ) )

( y A

nn nhE =

m D D D

+ +

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The three 4uantum num1ers n(, ny,and nAinde*endently can assume only

integer values 5n o(ygen molecule is confined in a cu1ic 1o( of volume 00 m"

5ssume that the molecule has an energy of $%9" > %0?)%2& tem*erature T = )

"% -hat is the value of )%

))) G 8y9 nnnn ++= for this moleculeR

")-hat is the energy se*aration 1et6een the levels n and n L %R

4 .n 4uantum mechanics, an energy level is said to 1e degenerate if it corres*onds

to t6o or more different measura1le states of a 4uantum system Consider a

*article in a cu1ic 1o( -hat is the degeneracy of the level that has energy )%O"

times that of the lo6est levelR

Problem ". #ug of war

Tug of war is a sport that directly pits two teams against each other in a test of strength.

This is also a traditional game of Vietnamese people

The follo6ing ta1le gives the standard molar 7i11s energy at different

tem*eratures for the reaction G% 1elo6:

S/"Gg S/) Gg L /) Gg G%

TOoC #)9 ##) $)9 $0 9)9r7oO2Bmol?% )%90! )0$)$ %!)%0 )! !#!

1Use the Van Hoffs e4uation to estimate the ln*%at each tem*erature

2 lot ln*%against %OT to determine the value of rHoin 2Bmol?%assuming that

rHodoes not vary significantly over the given tem*erature range

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Using the 1est3fit line to *lot a ln*%versus %OT, determine the *) for the

follo6ing reaction G) at $#%"" oC:

)S/"Gg )S/) Gg L /) Gg G)

4 5n amount of %#% g of iron G.. sulfate 6as heated in an evacuated %00 D

container to $#%"" oC, in 6hich the follo6ing reactions tae *lace:

'eS/! Gs 'e)/" Gs L S/" Gg L S/) Gg G"

)S/"Gg )S/) Gg L /) Gg G!

-hen the system has reached e4uili1rium, the *artial *ressure of o(ygen is of

)%) mmHg Calculate the e4uili1rium *ressure of the gases and the value of *"

for the reaction G" at e4uili1rium

Calculate the *ercentage of 'eS/!decom*osedR

Problem $. %adioc&emistry

Fircon GFrSi/! is a mineral found a1undantly in *lacer de*osits located in the

central coast of Vietnam @esides 1eing 6idely utiliAed in the ceramic industry,Aircon is also used as a ra6 material for the manufacture of Aircaloy 6hich is used

to 1uild fuel rods that hold the uranium dio(ide GU/) fuel *ellets in nuclear

reactors Fircon ore contains a trace amount of uranium, and it is not a via1le

source of uranium in *ractice Ho6ever, Aircon crystals mae a *erfect storage

medium to avoid the loss of uranium and lead G1 isoto*es 1ecause of its sta1le

crystal structure This allo6s develo*ing uranium3lead dating methodThere are " naturally occurring decay series:

3 The thorium series 1egins 6ith )")Th and ends u* 6ith )01

3 The uranium series Galso referred to as the uranium3radium series is headed

1y )"U The half3life Gt%O) of )"U is !!9 > %0years

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, %9


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3 The actinium series is headed 1y )"#U 6ith the half3life of 90" >

%0years

'our sta1le isoto*es of 1 e(ist in nature: )0!1, )0$1, )091, and )01 The natural

a1undance of each isoto*e is sho6n in the follo6ing ta1le

)0!1 )0$1 )091 )01%! )!% ))% #)!

5n analysis of a Aircon mineral sam*le gives the follo6ing mass ratios of U and 1

isoto*es:

mG)"U : mG)"#U : mG)0$1 : mG)0!1 = )9# : 09)% : %!"0 : 0)99

1 .ndicate the sta1le isoto*e of 1 6hich is not involved in the a1ove decay series

2 ;etermine the mass ratio of )"U to )"#U 6hen the Aircon mineral 6as first

formed 5ssume that the mineral already contained natural 1 right at the onset of

its formation+

roduction of uranium from lo63grade 6ill encounter many difficulties, nota1ly

large concentration of im*urities and lo6 concentrations of uranium in leach

solutions Various technological advances have 1een a**lied to overcome the

aforementioned *ro1lems& these include fractional *reci*itation, li4uid3li4uid

e(traction, or ion e(change methods

.n an e(*eriment to e(tract uranium from sam*le of lo6 uranium content using

diluted H)S/!, in the *reliminary treated leach solutions, the concentration of

uranyl sulfate GU/)S/! is 00% M and the concentration of ironG... sulfateG'e)GS/!" goes u* to 00# M The se*aration of uranium from iron and other

im*urities can 1e carried out 1y the fractional *reci*itation method

Calculate the *H necessary to *reci*itate of 'e"L6ithout losing uranium

ions 5ssume that the adsor*tion of uranium onto 'eG/H"is negligi1le Under the

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e(*erimental conditions, the solu1ility *roduct values for U/)G/H)and 'eG/H"

are %0 > %0?))and ">%0?", res*ectively

4/ne of the *ro*er methods to o1tain a rich uranium solution is the li4uid3li4uid

e(traction 6ith the organic *hase containing the e(tracted agent of

tri1utyl*hos*hate GT@ diluted in erosene -hen e(tracting uranium in the form

of uranyl nitrate GU/)GN/") under a**ro*riate conditions, the relationshi*

1et6een the concentrations of uranium in 6ater and organic *hases is given 1y:

;istri1ution coefficient: ; =or$

a'

6

6= %0

6here: Corgand Ca4are the e4uili1rium concentrations GM of U/)GN/")in organic

and a4ueous *hases, res*ectively

Calculate the mole *ercentage Gin com*arison 6ith the initial concentration of

U/)GN/")remaining in the a4ueous *hase after e(tracting %0 D of the solution

G6ith an initial concentration of 00% M 6ith #00 mD of organic solvent

ro*ose a scheme to e(tract $ of U/)GN/")from %0 D of the a4ueous *hase

into #00 mD of the organic *hase 5ssume that the distri1ution coefficient remainsconstant throughout the e(traction *rocess G; = %0

Problem '. Applied t&ermodynamics

1.n a**lied thermodynamics, 7i11s free energy *lays an im*ortant role and can1e calculated according to the follo6ing e(*ression:

7o)= Ho)? TSo)

7o) 3 standard free energy change

Ho) 3standard enthal*y change

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, %


20/92



So) 3 standard entro*y change

The 1urning of gra*hite is re*resented 1y t6o reactions:

C Ggra*hite L /) Gg C/ Gg G%

C Ggra*hite L /) Gg C/) Gg G)

The de*endence of Ho, Soon tem*erature is as follo6s:

8eaction G%: HoT G% G2Bmol3% = ?%%)) L #!T&

SoT G% G2B3%Bmol3% = #!0 L $)%lnT

8eaction G): HoT G) G2Bmol3% = ? ""9!0% L 099T&

SoT G) G2B3%Bmol3% = %#! ? 099lnT

@ased on the a1ove data:

%% ;erive the e(*ression for the 7i11s free energy as a function of tem*erature,

7oT= fGT for each reaction

%) redict the changes of 7oT6ith an increase in tem*erature

2 5ssume that at %!00 oC, during the course of reactions G% and G), C/ gas might

continue to react 6ith /)to form the final *roduct C/)

)% -rite do6n the reaction G" for the formation of C/)from C/ gas

)) Calculate 7oT G"

)" ;etermine the e4uili1rium constantK*for reaction G" at the given tem*erature

.n an e(*eriment, Ni/ *o6der and C/ gas 6ere *laced in a closed container

6hich 6as then heated u* to %!00 oC -hen the system reached e4uili1rium, there

6ere four s*ecies *resent: Ni/Gs, NiGs, C/Gg and C/)Gg The mole *ercentages

of C/ and C/)are % and , res*ectively, and the *ressure of the system is

%0 1ar G%0#a

"% -rite do6n the reactions in the a1ove e(*eriment

") @ased on the e(*erimental results and the a1ove thermodynamic data, calculate

the *ressure of /)in the e4uili1rium 6ith Ni/ and Ni at %!00 oC

Chemistry The flavor of life )0


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Problem (. Comple! compounds

Ethylenediamine tetraacetic acid GE;T5 is used as a reagent to titrate the

metal ions in the com*le(ometric titration

E;T5 is a tetra*rotic acid, a11reviated as H!W, 6ith the structure:

5s E;T5 is s*aringly solu1le in 6ater, a more solu1le sodium form, Na )H)W, is

usually used and H)W)X is commonly no6n as E;T5 E;T5 forms strong %:%

com*le(es 6ith most metal ions MnL

1 Ho6 many atoms of an E;T5 molecule are ca*a1le of 1inding 6ith the metal

ion u*on com*le(ationR

%% Chec in the a**ro*riate 1o(

) ! $

%) ;ra6 the structure of the com*le( of a metal ion M)L6ith E;T5

2 Com*le(ation reaction 1et6een W!X form of E;T5 and metal ion MnL has a large

formation constant Gsta1ility constant Y:

MnL L W!X MWG!XnXZZ[[

Z[!

!G

+

=

:;

;:n

n

@esides com*le(ation reaction 1et6een W!X form of E;T5 and metal ion MnL,

other *rocesses in the solution also develo* such as formation of hydro(o

com*le(es of the metal ion, acid31ase e4uili1rium of H )W)XQ To account for such

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, )%


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*rocesses conditional formation constant Y is used for the calculations

Y is determined from Y as the follo6ing e(*ression:

nL !3

M WY = Y\ \

6here: !3W\ and nLM\ are fractions of W!? G !3W\

=

4[Y ]

[Y]' and free metal ion MnL G

nLM\ = [M ]

[M]', 6ith [WZand [MZ1eing the total concentrations of all forms of W!X

and MnL, e(cluding MWG!XnX 7iven that: H!W has *Ka%= )00& *Ka)= )$9& *Ka"=

$%$& and *Ka!= %0)$ (Ka vaues or :2= are i$nored)

)sGMgG/H * =%0#& $E,log ) =

;$:

Mg)LL H)/ Mg/HL L HL ]?= %#>%03%"& G*a= 3loga& *s= 3logs

.n a ty*ical e(*eriment, %00 mD of 0%0 M MgCl)solution and %00 mD of 0%0 M

Na)H)W solution are mi(ed together *H of the resulting solution is adPusted to

%0)$ 1y an NH"ONH!L1uffered solution

)% Calculate conditional formation constant G of the MgW)Xcom*le( at *H =

%0)$ given that acid31ase e4uili1rium of H)W)Xand formation of mononuclear

hydro(o com*le( of Mg)Loccur in the solution

)) ;oes the MgG/H)*reci*itate in this e(*erimentR Chec in the a**ro*riate 1o(

reci*itation No *reci*itation

.n order to titrate metal ions 1y E;T5, the conditional formation constant G

of the com*le( metal ? E;T5 GMWG!XnX must 1e large enough, usually %00 >

%0 3 %00 > %0 To determine the concentrations of Mn)Land Hg)Lin an analytical

sam*le, t6o e(*eriments are carried out

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39eriment 1!5dd )#00 mD of 00!0 M E;T5 solution to )000 mD of the

analytical solution 5dPust the *H of the resulting solution to %0#0 Titrate the

e(cess E;T5 6ith a suita1le indicator and %)00 mD of 00)# M Mg )Lsolution is

consumed

39eriment 2! ;issolve %!00 gram of CN into )000 mD of the analytical

solution Gassuming that the volume is unchanged u*on dissolution and then add

)#00 mD of 00!0 M E;T5 solution Titrate the e(cess E;T5 in the resulting

mi(ture at the *H of %0#0& )000 mD of 00)# M Mg)Lsolution is consumed

"% rove that: in the e(*eriment ), Hg)L cannot 1e determined 1y titration 6ith

E;T5 in the *resence of CN in solution Gor Hg )Lis mased in the com*le(

form of HgGCN!)3

") -rite do6n chemical e4uations for the reactions in the t6o e(*eriments and

calculate molar concentrations of Mn)L and Hg)L in the analytical solution

7iven that: "#&9"log&0)%log GG )!) === 26,a6,2$2$: K

G/ther *rocesses of Hg

)L

are ignored& the *

a

values of H

!

W are *rovided in

4uestion )

4 .n the titration of *oly*rotic acids or 1ases, if the ratios of consecutive

dissociation constants e(ceed %00>%0

!

, multi*le titrations are *ossi1le 6ith an

error less than % To ensure the allo6ed error, only acids or 1ases 6ith

e4uili1rium constants larger than %00>%0

3

can 1e titrated To find the end3*oint,

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, )"


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*H range of the indicator must 1e close to that of the e4uivalence *oint

G*H

E

& the *oint at 6hich the stoichiometric amounts of analyte and titrant has

reacted Titrate %000 mD of 0)# M Na)

H)

W solution 1y 0)0 M Na/H solution in

a ty*ical e(*eriment

!% -rite do6n the chemical e4uation for the titration reaction

!) ;etermine the value of *HE

!" Choose the most suita1le indicator Gchec in the a**ro*riate 1o( for the a1ove

titration from the follo6ing: 1romothymol 1lue G*H = 9$0& *henol red G*H =

)0& *henol*htalein G*H = 00

@romothymol 1lue henol red henol*htalein

!! Titration error 'defined as the difference 1et6een the titrant amount added and

the titrant amount needed to reach the e4uivalence *oint is e(*ressed as:

%00%00)

)%

)

)%

=

=)

))

)6

)6)6'

,a%2

,a%2,a%2

Chemistry The flavor of life )!


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6here CNa/H

is the Na/H concentration& V%

: End3*oint volume of Na/H& V)

:

e4uivalence *oint volume of Na/H

Calculate the consumed volume of Na/H solution and the titration error if the final

*H is 9$0

Problem ). *ead compounds

1 Consider the follo6ing nuclide: )0@iG., )01G.., )091G..., )0$1G.V -hich

nuclide is the last mem1er of the decay series for )"UR Chec in the a**ro*riate

1o(

G. G.. G... G.V

2 There are three natural decay series They 1egin 6ith Th3)")G., U3)"G.., U3

)"#G... and end 6ith 13)0, 13)0$, 13)09 .n 6hich decay chain are there $ @

decays and !?decaysR Choose the correct ans6er 1y checing in the a**ro*riate

1o(

G. G.. G... None

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, )#


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1GN/") solution is slo6ly added into )000 mD of a mi(ture

consisting of 00)0 M Na)S/!& #0>%0X"M Na)C)/!& 9>%0X"M .& 00# M Cl

and 000%0 M ./" -hen the 1right yello6 *reci*itate of 1.)1egins to form,

)%$0 mD of 1GN/")solution is consumed

"% ;etermine the order of *reci*itationR

") Calculate the concentration of 1GN/") solutionR

7iven that:!sG1S/

* = 9$$&" )sG1G./

* = %)$%&)sG1.

* = 9$&) !sG1C /

*

= %00#& 99!G ) =/b61sK (%ther rocesses o the ions are i$nored)+

4/ne of the common reagents to detect 1)Ls*ecies is )Cr/!, giving yello6

*reci*itate 1Cr/!, 6hich is solu1le in e(cess of Na/H The solu1ility of 1Cr/ !

de*ends not only on *H 1ut also on the *resence of coordinating s*ecies 7iven

that the solu1ility of 1Cr/! in % M acetic acid solution is s = )>%0X# M,

calculate the solu1ility *roduct s*of 1Cr/!

&9$,!G " =6%%262aK &$,)lg G " =+6%%62/b &0,!lg )" G =6%%62/b

#,$G !=

26r%aK

1)LL H)/ 1/HL L HL ]?= %039

Cr)/9)3 L H)/ )Cr/!)3L )HL K= %03%!,$!

Dead3acid 1attery, commonly no6n as lead 1attery consists of t6o lead *lates a

*ositive electrode covered 6ith a *aste of lead dio(ide and a negative electrode

made of s*onge lead The electrodes are su1mersed in an electrolyte consisting of

6ater and sulfuric acid H)S/! -rite the chemical e4uations for *rocesses on each

electrode, overall reaction as the 1attery discharges and the cell diagram

7iven that: &%)$,00 O) )3 /b/b =+ ))0

O%!## &

/b% /b3 + = &00,)G ! =2S%aK

&$$,9G ! =/bS%sK at )#oC: )

F

RT0#E),0"0",) =

6 Calculate:

Chemistry The flavor of life )$


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$%!

01S/ O1E & ) !

01/ O1S/E

$) The *otential V of the lead 1attery if ) !H S/6 % M

Problem 1+. Applied electroc&emistry

18eduction3o(idation reactions have *layed an im*ortant role in chemistry due to

their *otential to 1e valua1le sources of energy for technology and life -rite do6n

chemical e4uations for the follo6ing reactions:

%% /(idation of glucose GC$H%)/$ 6ith Mn/! solution in the *resence of

sulfuric acid to form gaseous C/)

%) /(idation of 'eS/! 6ith Mn/!in an acidic medium Gsulfuric acid to form

'e)GS/!"

%" @ased on the reaction in section %), determine the anodic reaction and

cathodic reaction and the relevant cell diagram

%! ;erive the e(*ression for electromotive force E of the cell2 .n the thermodynamics *oint of vie6, 7i11s free energy 7 at constant , T

condition is closely related to electromotive force E of a redo( reaction according

to 1elo6 e(*ression:

G n F E = G

En F

=

6here: n ? num1er of electrons transferred,

' ? 'araday constant

The correlation of the standard reduction *otential 1et6een Mn ions in acidic

medium is:

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, )9


28/92



++++

)#%,%"R

)

R)

!

#$,0

!

0

!

0

" ;n;n;n%;n%;n% )33)

L%9V L%)"V

)% ;etermine the standard reduction *otential of the *air)

)

!

;n%;n%

)) ;etermine the standard reduction *otential of the *air +")

;n

;n%

5 *rocess is s*ontaneous if 7i11s free energy is negative @ased on the

thermodynamic data:

"% ;etermine 7i11s free energy of the follo6ing reaction:

"Mn/!)3

L !HL

)Mn/!3

L Mn/)L )H)/") .s the reaction s*ontaneousR

"" CalculateKcfor the reaction

Problem 11. P&osp&oric acid

/is a solution of H"/!6ith *H of %!$

1Calculate the molar concentrations of all s*ecies in solution / 7iven thatKa

values for H"/!are 9#>%0X"& $)>%0Xand !>%0X%", res*ectively

2Mi(ing of #0 ml of solution /and #0 ml of 0! M NH"solution results in %00

ml of solution B Calculate *H of solution BG )!!

=+,2K

%00 mD of solution B is mi(ed 6ith %00 ml of 0) M MgGN/") solution

;etermine if *reci*itate of NH!Mg/!forms The hydrolysis of Mg)L is ignored

and *reci*itation of NH!Mg/!is assumed to 1e the only reaction, given thatKs*=

)#>%0X%"

4 Calculate the solu1ility GmolBDX% of Ca"G/!), givenKs*= )))>%0X)#

(int! The hydroysis o 6a2=is i$nored)+

Chemistry The flavor of life )


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Problem 12. C&emical inetics

Thermal decom*osition of dinitrogen *ento(ide GN)/# in the gas *hase has time3

inde*endent stoichiometry

) N)/#Gg ! N/) Gg L /) Gg G%

5 inetic measurement for N)/#at $"" oC is sho6n in 'igure % 1elo6

0,00EL00

#,00E30!

%,00E30"

%,#0E30"

),00E30"

),#0E30"

",00E30"

",#0E30"

!,00E30"

0 %00 )00 "00 !00 #00 $00 900 00 00

+ime4 s

562O74mol(dm

-1

562O7

Fi$ure 1 Concentration of N)/#versus time

1-hat is the half3life Gt%O) for the decom*osition of N)/#at $"" oCR

2The reaction order for the reaction G% can 1e determined 1y *lotting of ln

[N)/#Z0O[N)/#Ztversustime or ^[N)/#Z0O[N)/#Zt 3%_ versustime

)% lot the gra*hs into the t6o figures 1elo6 to determine the reaction orderR

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!,

Time

Gs

[N)/#ZO

molBdmX"

0 "0>%0X"

#0 ")!>%0X"

%00 )$">%0X"

%#0 )%">%0X"

))# %##>%0X"

"#0 )0>%0X!

#%0 !90>%0X!$#0 )$%>%0X!

00 %">%0X!

)


30/92



)) -rite do6n the rate la6 and integrated rate e4uation

0

0#

%

%#

)

)#

"

"#

!

0 %00 )00 "00 !00 #00 $00 900 00 00

TimeO s

ln^562O704562O7t_

Fi$ure 25 re3*lot of the data in 'igure % as function of ln [N)/#Z0O[N)/#Zt_ versus time

0

#

%0

%#

)0

)#

"0

0 %00 )00 "00 !00 #00 $00 900 00 E00

+ime4 s

8562O704562O7t9-1

Fi$ure A+5 re3*lot of the data in 'igure % as function of [N)/#Z0O[N)/#Zt3%_ versus time

;etermine the rate constant for the reaction G%

4 The rate constant for G% at !# oC is of #0)>%03!sX% Calculate the activation

energy GEa and *re3e(*onential factor G5 for the reaction G% assuming that the

activation energy and *re3e(*onential factor are tem*erature inde*endent

The follo6ing mechanism is *ro*osed for the reaction G%:

Chemistry The flavor of life "0


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N)/# N/) L N/" G)

N/) L N/" N/) L /) L N/ G"

N/ L N/" ) N/) G!

Using this mechanism, derive the rate la6 for 3d[N)/#ZOdt assuming that the

intermediate concentrations can 1e treated 1y the steady3state a**ro(imation

Problem 13. inetics of t&e decomposition of &ydrogen pero!ide

.n order to decom*ose hydrogen *ero(ide GH)/) 6ith iodide ion as catalyst in

neutral solution, the " H)/)solution G6hich a**ro(imately corres*onds to "0 g

of H)/) in % D of solution is mi(ed 6ith 0% M . solution and 6ater at different

volumetric ratios& and the volume of the o(ygen gas released G) m5)% is

measured

E(*eriment G))m5) %2 Gm5)K# G) m5) %2 minOG) m5)%

at ) and % atm% )# #0 9# !!) #0 #0 #0 #" %00 #0 0 %9#! #0 )# 9# !)## #0 %00 0 %$#

1 ;etermine the reaction order 6ith res*ect to H)/),and .3, res*ectively

2 -rite do6n the chemical reaction, and determine the rate la6

Calculate the molarity of H)/)at the 1eginning of the e(*eriment `! and after ! min

4 The reaction mechanism involves a series of the follo6ing ste*s:

H)/) L .X %- H)/ L ./X G%

./X L H)/) )- /) L .X G)

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, "%


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;o the t6o a1ove ste*s have the same rate or different ratesR -hich ste*

determines the overall rate of the o(ygen releaseR 2ustify your ans6er

Problem 14. agnetism of transition metal comple!es

5 transition metal com*le( containing diamagnetic ligands can 1e overall

diama$netic Gall electrons are *aired or arama$netic Ghaving un*aired

electronGs de*ending on the electronic configuration of the central metal ion, the

nature of the ligand, and geometry of the ligand s*here The magnitude of

*aramagnetism of a metal com*le( is commonly re*orted in terms of the effective

magnetic moment GJeff 6hich can 1e o1tained from the e(*erimental measurement

of molar magnetic susce*ti1ility GKm and is commonly e(*ressed in @ohr

magneton G@M

Theoretically, the magnetic moment is contri1uted 1y t6o com*onents, the s*in

angular momentum and the or1ital angular momentum 'or many com*le(es offirst ro6 d31loc metal ions, ho6ever, the contri1ution of the second com*onent

can 1e ignored Thus, the so3called s*in only magnetic moment can 1e determined

1y the num1er of un*aired electrons, n:

1 The o1served effective magnetic moment of t6o octahedral com*le(es,

![MnGCN$Z"H)/ and ![MnGSCN$Z are )% @M and $0$ @M, res*ectively%% Calculate num1er of un*aired electrons in each com*le( -hich com*le( is

lo6 s*inR -hich com*le( is high s*inR

%) 8ationaliAe your ans6ers 1y a**lying crystal field theory

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2 Calculate the J Gs*in only of com*le( [NiGH)/$ZCl)

.n *ractice, the e(*erimentally o1served Jeffvalue of [NiGH)/$ZCl)is ")# @M

This is not sur*rising due to the fact that magnetic moment of octahedralcom*le(es of Ni)LGd usually does not o1ey the s*in only formula .n these cases,

the contri1ution of or1ital angular momentum should 1e taen into account The

sim*lification of s*in3or1it cou*ling model can 1e a**lied to calculate their

magnetic moment:

6here is s*in3or1it cou*ling constant of Ni)Land has the value of "%# cmX%

octis the crystal3field s*litting *arameter

Calculate the effective magnetic moment of [NiGH)/$ZCl) taing into account

s*in?or1it cou*ling octof [NiGH)/$Z)Lis #00 cm3%

4 ;i1enAoylmethane G;@M is a 6ell no6n chelating b3/,/3ligand 6hich can

form sta1le com*le(es 6ith many transition metal ions

3B

8eaction of NiGCH"C//)!H)/ 6ith ;@M in Et/H 3 H)/ solution gives light

green crystalline com*le( /6hich loses $ of mass on heating at )%0 oC in the

air to form green solid B The su1stance Bis 4uantitatively converted to 1ro6n

*rismatic crystals C 1y re3crystalliAation in dry toluene B and C are t6o

*olymor*hic forms and their inter3conversion is reversi1le The 3ray single

crystal structure of C sho6s a s4uare *lanar geometry 6ith the chemical

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, ""


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com*osition of [NiG;@M)Z -hile B is *aramagnetic 6ith effective

magnetic moment of ")9 @M, the com*le( Cis diamagnetic -hen Band Care

e*t in the air, they slo6ly convert to /This ha**ens much faster in the *resence

of some organic solvents G#nor$+ 6hem+, 2001, 40, 1>2>1>A>

!% ;ra6 the s*litting diagram of the d or1itals of Ni)L in C and confirm its

diamagnetic *ro*erty

!) -hat is the molecular formula of /R 5ssume that / is a mononuclear

com*le(

!" The effective magnetic moment of /is "%% @M GSynth+ React+ #nor$+ ;et+ %r$+

6hem+, 200B, AB, >B4C0A) -hat is the most suita1le molecular geometry of /R

G5ssuming that .f 5 is an octahedral com*le(es, octof /is similar to that of

[NiGH)/$Z)L

!! ;ra6 all *ossi1le isomers of /

!# -hat do you e(*ect for the molecular geometry of BR

Problem 1". tructure and synt&esis of Al-eggin ion

15 molecular dimer of aluminum chloride in gas *hase has the structure:

Chemistry The flavor of life "!


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%% -hat is the hy1ridiAation of the 5l atoms in a dimerR

%) ;etermine the distance 1et6een t6o 5l atoms

25luminum chloride dissociates in 1asic solution yielding several 5l3*olycations5 ty*ical 5l3eggin ion 6ith the molecular formula of [5l%"/)H)!%)H)/ZCln6as

formed at a hydrolysis ratio [/H3ZO[5l"LZ of %# to )# .t is only com*osed of

tetrahedral and octahedral 5l cations The )95l NM8 s*ectrum of an 5l%" ion is

sho6n 1elo6 The shar* signal at $! **m is due to the very symmetrical

environment of the corres*onding 5l atomGs in the eggin cation

)% ;etermine the a1solute value of Gn in the 5l%"eggin ion

)) 5ssign )95l NM8 signals in the s*ectrum to the a**ro*riate 5l cationGs in the

right figure

)" .n an 5l%"3eggin ion, 5l tetrahedronGs isGare only lined 6ith other 5l atoms

1y the o(ygen 1ridge ro*ose the structural formula for the 5l%"3eggin ion

)! ;etermine the num1er of o(ygen atoms 1ridging adPacent octahedra)# -rite do6n the overall e4uation to *re*are 5l3eggin ions from the reaction

1et6een Na/H and 5lCl"solution

5l%"3eggin ions have recently 1een *re*ared 1y solid 3 solid interaction

referred to as mechanochemical synthesis [D+ 6ata+ 24< (200C) A4>& #nor$+ 6hem+

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, "#


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6ommun+ 11 (2008) 112


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I#

a1sor*tion,

C3C%0, cm3%

%H NM8 signals of aromatic *rotons, G**m

Uncoordinated %$"0

Coordinated in

/%#%0

Coordinated in

B%!#

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, "9


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Coordinated in

C

%#00

1-rite 1alanced e4uations for the three reactions in the a1ove scheme

2 -hat information a1out the coordination of safrole 6ith t in /, Band C can 1e

o1tained from the .8 and %H NM8 dataR

;ra6 the structures of /, Band C, given that in C*yridine is in the cis*osition

6ith res*ect to the allyl grou* of safrole

4-hat is the driving force of each of the reactions G%, G) and G"R

-hy does reaction " not seem to o1ey the trans eectR

Problem 1'. /mida0ole

Heterocyclic chemistry is one of the most im*ortant fields of organic chemistryand 1iochemistry 5**ro(imately ## of *u1lications in organic chemistry are

related to the field, and the num1er of heterocyclic com*ounds recently found is

far more than that of homocyclic com*ounds The five3mem1ered ring com*ounds

6ith t6o heteroatoms are often *resent in many su1stances that are im*ortant for

life 'or e(am*le, imidaAole ring is *resent in the essential amino acid, histidine,

and its decar1o(ylation *roduct, histamine Histidine residues are found at the

active sites of ri1onuclease and of several other enAymes and *lay a vital *art in the

structure and 1inding functions of hemoglo1in Several drugs are 1ased on the

imidaAole ring such as nitroimidaAole, cimetidine, aAomicin, metronidaAole,

medaAolam

Chemistry The flavor of life "


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1 ;ra6 the structures of %,"3diaAole GimidaAole, C"H!N), imidaAol3%3ide anion,

imidaAolium cation, %,"3o(aAole Go(aAole, C"H"N/ and %,"3thiaAole GthiaAole,

C"H"NS -hich structureGs can 1e considered aromaticR

2 5rrange imidaAole, %,"3o(aAole and %,"3thiaAole in decreasing order of melting

and 1oiling *oints and Pustify your order

Using structural formulae, 6rite do6n e4uations for the ioniAation of imidaAole,

o(aAole, and thiaAole in 6ater 5rrange the su1stances in decreasing order of 1ase

strength and Pustify your ans6er

4 ro*ose a reaction mechanism sho6ing the catalytic 1ehavior of imidaAole in

hydrolyAing 8C//8 6ithout a *artici*ation of /H? 2ustify this 1ehavior 1ased

on the structure of imidaAole

ro*ose a reaction mechanism for the formation of %,%3car1onyldiimidaAole

GC9H$N!/, C;. from imidaAole and *hosgen GC/Cl)

6 E(*lain 6hy the C=/ stretching fre4uency in %,%3car1onyldiimidaAole is %00

cm?% higher than that of %,%3car1onyldi*yrrolidine GC/GC!HN)

: -rite do6n reaction e4uations for the *re*aration of C;. Ga using a mi(ture of

! mol imidaAole and % mol *hosgene and G1 using a mi(ture of ) mol imidaAole, %

mol *hosgene, and ) mol Na/H E(*lain 6hy reaction Ga is *refera1le

! C;. is often used for the activation of car1onyl grou* for the cou*ling of amino

acids in *e*tide synthesis

% Use curly arro6 mechanisms to com*lete the scheme 1elo6, sho6ing the

formation of the active com*ound ;from C;. and 5lanine

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, "


40/92



) ro*ose a reaction mechanism for the formation of di*e*tide 5la37ly from ;

and 7lycine

Problem 1(. mall &eterocycles

Heterocyclic com*ounds containing the C'" grou* are interesting targets of

advanced researches to generate 1iologically active com*ounds .t is 4uite difficultto 1ring the trifluoromethyl grou* into saturated heterocyclic structures, es*ecially

heterocycles containing nitrogen Ho6ever, these heterocyles 1earing C'"grou*s

have several *romising a**lications Therefore, studies of such com*ounds have

1een carried out 1y many chemists

Trifluoroacetaldehyde G/ 6as treated 6ith ethanol and then reflu(ed 6ith

1enAylamine in toluene to afford com*ound B GCHN'" The reaction of

com*ound B6ith ethyl diaAoacetate in diethyl ether 6ith 1orontrifluoride etherate

G@'"Et)/ as a catalyst at 39 oC for ! hours *rovided com*ound CGC%"H%!N/)'"

The reduction of com*ound C1y Di5lH!in TH' at room tem*erature for ) hours

formed com*ound 3 Then, 3reacts 6ith hydrogen in the *resence of dG/H)as

Chemistry The flavor of life !0


41/92



a catalyst in CH)Cl)at room tem*erature for $0 hours to o1tain E GC!H$N/'"

Com*ound E6as then allo6ed to react 6ith ) e4uivalents of tosyl chloride GTsCl

in dicloethane 6ith the catalytic Et"N and amount of !3dimetylamino*yridine

G;M5 The reaction 6as carried out at room tem*erature for ) hours, then "

hours of reflu(, to furnish com*ound F Freacted 6ith %) e4uivalents of *henol in

the *resence of )C/"in ;M' to form com*ound ;GC%9H%$NS/"'"

5 derivative of ;can 1e synthesiAed according to the follo6ing diagram:

1Com*lete synthetic schemes from Bto


42/92



Vitamin H or 1iotin is a highly effective gro6th *romoter 6hich *lays an

im*ortant role in many organisms, for instance 1aers yeast GSaccharomyces

corevisiae Human 1eings have different demand in 1iotin de*ending on age Dac

of 1iotin can lead to diseases such as dermatitis, a1sence of a**etite, fatigue,

muscular *ain and nerve *ertur1ance

@iotin 6as first found in %0% 1y -ildiers as a gro6th3*romoting vitamin of

yeasts Thereafter, it 6as found in egg yol G1y gl, %"$ and in liver G1y SAent3

7yrgyi, %"$ The a1solute configurations of chiral car1ons of 1iotin 6ere

esta1lished 1y Trotter and Hamilton in %$$ 1y the single3crystal 38ay

diffraction The molecule of 1iotin has three chiral car1ons Hence, there are

theoretically eight diastereomers /nly the GAaS, 4S, >aR3(7)3GL31iotin, ho6ever,

sho6s the high 1ioactivity

.n %), researchers from Hoffmann3Da 8oche *u1lished an elegant synthesis

*rocedure for G73GL3@iotin from the methyl ester of the amino acid D3Cysteine

6ith the follo6ing ste*s

1 The thiol grou* of the methyl ester of D3cysteine 6as transformed into a

disulfide S3S 1ond Gcom*ound / in an o(idation reaction /6as then treated 6ith

he(3#3inoyl chloride to give com*ound B 6hich 6as su1se4uently reduced 1y

FnOCH"C//H to afford a thiol This com*ound 6as cycliAed 1y the addition of the

Chemistry The flavor of life !)


43/92



?SH grou* to the terminal alyne under atmos*heric condition, resulting in the

formation of C6ith a ten3mem1ered ring containing a GE C=C dou1le 1ond -rite

do6n the structural formulae of /, Band Cin the hereunder scheme

2 The reduction of C 1y diiso1utylaluminium hydride GGi3@u)5lH, ;.@5D

resulted in the formation of G3 The condensation reaction 1et6een 3 and

1enAylhydro(ylamine in dichloromethane *roduced nitrone E Ga nitrone is an

organic com*ound 6hich contains a C=NL3/3 grou* Eunder6ent a %,"3di*olar

intramolecular cycliAation reaction to afford *olycyclic com*ound Fof 6hich the

t6o heterocycles, iso(aAolidine G%,)3o(aAolidine and tetrahydrothio*hene, shared

a common 1ond The cycliAation reaction resulted in the GS configurations of thet6o car1ons at the common 1ond and the GR configuration of the car1on

connected to the o(ygen -rite do6n the structural formulae of 3, Eand F

-hen F 6as reduced 6ith Fn *o6der in acetic acid, the N3/ 1ond of the

heterocycle iso(aAolidine 6as 1roen to give com*ound ; The reaction 1et6een;and chloroformate in the *resence of Na)C/"in TH' resulted in the formation

of com*ound % The treatment of % in a hot solution of @aG/H) in dio(ane,

follo6ed 1y an acidic 6or3u* yielded the 1icyclic 3hydro(y acid Icontaining all

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, !"

5ir, )# oC


44/92



the chiral centers of G73GL3@iotin 1ut 6ith an e(cessive 3/H grou*

;ra6 the structures of ;, %and Iand e(*lain the formation of Ifrom %

4I6as treated 6ith S/Cl)to yield the corres*onding chloride acid =, given that

the configuration of the car1on attached to the e(cessive 3/H is maintained in =

Ester


45/92



;ue to its im*ortant role in *erfume industry as 6ell as its limited natural resource,

the synthesis of Pasmonates has attracted interest of many chemists The first

synthesis of o*tically *ure GE3GAR,CS3methyl Pasmonate 6as carried out in %0

1y Helmchen 6ith the follo6ing ste*s:1 The first ste* in the synthesis is a ;iels35lder reaction 1et6een cyclo*entadiene

/and ester Bof fumaric acid 6ith GS3ethyl lactate to yield C

5 cyclo3addition reaction, a ind of *ericyclic reaction, involves 1onding

1et6een the termini of t6o j systems to *roduce a ne6 ring Gscheme 1elo6 The

*roduct has t6o more k 1onds and t6o less j 1onds than the reactants The ;iels3

5lder reaction, or so called [!L)Z, is a common thermally activated cycloaddition

6hose stereoselectivity is syn addition .n this concerted syn addition, the

stereochemical relationshi*s among the su1stituents are retained in the *roductGs

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, !#

methyl Pasmonate methyl Pasmonate


46/92



The hydrolysis of Cin 1asic solution follo6ed 1y an acidification ste*

resulted in the formation of 3 ;ra6 the structures of Cand 3

2 The reaction 1et6een 3and .)in . solution gave rise to the formation of the 3iodolacton of the endo ?C//H grou* -hen heated under 1asic condition, E

under6ent a decar1o(ylation3cycliAation reaction to *roduce com*ound F The

hydrolysis in 1asic medium follo6ed 1y o(idation 6ith Na./!O8u/!transformed F

into 3eto acid ; -rite do6n the structures of Eto ;

;6as reacted 6ith H. to yield com*ound % containing only five3mem1ered

rings -hen %6as reduced 1y FnOH)/!in tetrahydrofuran, it transformed into

car1o(ylic acid I6hich 6as then o(idiAed in a @ayer3Villiger rearrangement 6ith

meta3chloro*ero(y1enAoic acid Gm3C@5 to give the maPor *roduct = = 6as

treated 6ith o(aloyl chloride, follo6ed 1y a dO@aS/!catalyAed reduction 6ith H)

G8osenmund reduction to give


47/92



4 Hydrolysis of in TH'OH)/ solution of acetic acid *roduced 6hich

under6ent a -ittig reaction 6ith the ylide h" = CHCH)CH" to form O The

hydrolysis of O in 1asic solution, follo6ed 1y a neutraliAation ste* and then

treatment 6ith diaAomethane resulted in the formation of P .n the last ste*, the

target molecule, GE3GAR,CS3methyl Pasmonate >, 6as o1tained in the o(idation

reaction of P6ith *yridinium dichromate ;ra6 the structures of com*ounds from

to P

Problem 21. ietnamese cinnamon

6innamomum oureiroi, also no6n as Vietnamese cinnamon, is an evergreen

tree gro6n in the central and northern regions of Vietnam 5romatic 1ar of the

tree has medicinal and culinary value Essential oil of the 1ar contains

cinnamaldehyde GG)33"3*henyl*ro*3)3enal as the main com*onent

Mild o(idation of cinnamaldehyde 6ith NaCl/)affords an acid / /undergoes

su1se4uent esterification 6ith ethanol to form ethyl cinnamate GB 8eflu(ing ethyl

cinnamate and 0 hydraAine hydrate solution for %0 h gives C GCH%0N)/

8eflu(ing Cand3nitro1enAaldehyde in ethanol for %) h affords 3GC%$H%"N"/"

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, !9


48/92



%H NM8 s*ectra of Cand 3are given 1elo6 Gthe multi*licity and relative intensity

is sho6n for each signal

17ive the structures for /, B,C

Chemistry The flavor of life !


49/92



2 5ssign %H NM8 signals in the first s*ectrum to a**ro*riate *roton grou*s of C

ro*ose a reaction mechanism for the formation of C from B

45mong four given 1elo6 structures, select one for 3and give the reasons for

your selection

5ssign %H NM8 signals in the second s*ectrum to a**ro*riate *roton grou*s of 3

Problem 22. Cinnamic acid

1 Ultraviolet irradiation oftrans3cinnamic acid GG33"3*henyl*ro*3)3enoic acid in

solution yielded a mi(ture of cis3cinnamic and trans3cinnamic acids trans3

Cinnamic acid can 1e crystalliAed in t6o forms: \3form or Y3form Ultraviolet

irradiation of crystalline trans3cinnamic acid in the \3form yielded \3tru(illic acid

G),!3di*henylcyclo1utane3%,"3dicar1o(ylic acid Ultraviolet irradiation ofcrystalline trans3cinnamic acid in the Y3form yielded Y3tru(inic acid G),"3

di*henylcyclo1utane3%,!3dicar1o(ylic acid \3Tru(illic acid *ossesses a

symmetric center .n Y3tru(inic acid, the t6o *henyl grou*s are on the same side of

the cyclo1utane ring, and the t6o car1o(yl grou*s are on the o**osite sides

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, !


50/92



%% ro*ose a reaction mechanism for the isomeriAation of trans3

cinnamic acid

%) ;ra6 the structure of \3tru(illic acid and all its diastereoisomers

%" ;ra6 the structure of Y3tru(inic acid and all its diastereoisomers Sho6 the

structures 6hich have enantiomers

%! Suggest ho6 the different *acing arrangements of trans3cinnamic acid in the

\3 and Y3 crystal forms leads to the different structures of \3tru(illic and Y3

tru(inic acid

%# -hy does cinnamic acid not dimeriAe in solution u*on ultraviolet irradiationR

2Hydrolysis of \3tru(illine GC"H!$N)/, an alaloid o1tained from Tru(illo coca

gives \3tru(illic acid, methanol and an acid / GCH%#N/" /(idation ofA ith

*yridinium chlorochromate GCC leads to B, hich is readiy decarbo9yated to

orm oticay inactive -etone C GCH%"N/ /(idation of C ith otassium

erman$anate $ives methysuccinimide+

2.1 Propose the structures of A, B, C. Are A, B optically active or not? Explain.

Why C is optically inactive?

)) ro*ose the structure of \3tru(illine .s \3tru(illine o*tically active or notR E(*lain

Problem 23. #ris5trimet&ylsilyl6silane and a0obisisobutyronitrile

Chemistry The flavor of life #0


51/92



.n the late eighties, Chatgilialoglu and co6orers introduced

trisGtrimethylsilylsilane, GTTMSS or GTMS"SiH as a radical31ased reducing

agent for functional grou* modifications and a mediator for se4uential radical

reactions The use of GTMS"SiH allo6s reactions to 1e carried out under mild

conditions 6ith e(cellent yields of *roducts and remara1le chemo3, regio3, and

stereoselectivity GTMS"SiH is an effective reducing agent for the removal of a

variety of functional grou*s E(am*les of dehalogenation GCl, @r and . and

reductive removal of chalcogen grou*s GS8 and Se8 are 6ell no6n The most

*o*ular thermal initiator is aAo1isiso1utyronitrile, ^5.@N, [GCH")CGCNZ)N)_

under heating conditions in toluene

1 8eactions using TTMSS and 5.@N are given in the hereunder e(am*les

%% 8adical cyclisation 6as studied using t6o different reducing agents: tri1utyltin

hydride GT@TH, @u"SnH and trisGtrimethylsilylsilane GTTMSS

N

'


52/92



)% The com*ound GI 6as converted to B and C via the radical

intermediate /

/

O

TTMSS ? A.BN

Be!@e!e> re0l#A C

'e-#c2ie :r"-#c2 C8cli&a2i"! :r"-#c2

)) The com*ound GII 6as converted to 3

O

O

Br

O

TTMSSA.BN>

D

)" The com*ound GIII 6as converted to E" and then through several ste*s to

afford G 3 vindoline

N

/

MeO

N3

OB!

Me

TTMSS ? A.BN

T"l#e!e> "7

OMe

Me CO2Me

N

N

OAc

HO

)! Horsfiline G? is an o(indole alaloid found in the *lant orsiedia suerba,

6hich has analgesic effects The method for horsfiline synthesis from the

com*ound GI& 6as descri1ed 1elo6:

N3

8

MeO /

N

B!

TTMSS ? A.BN

Be!@e!e> 9 :/

;

H

D N2MeO

N

O

B!

NMe

?DDH"r&ili!e

-rite do6n the structural formulae of all com*ounds / toIgiven in the a1ove reactions

Chemistry The flavor of life #)

G3Vindoline


53/92



Problem 24. 5-3-Carene

Carene, or 3"3carene, is a 1icyclic monoter*ene 6hich occurs naturally as a

constituent of tur*entine GL33"3Carene has the re4uired structural features to

serve as a starting material for G33menthol

The *rocedure of *re*aration of G33menthol from GL33"3carene 6as descri1ed as follo6s

Catalytic isomeriAation of 3"3carene *rovides the needed GL33)3carene G/

6hich then 6as *yrolysed to cleave the cyclo*ro*ane ring The resultant ),3

menthaldien GB had the right stereochemistry at C% and C! of G?3menthol

Treatment of the unconPugated diene B6ith % e4uivalent mole of HCl gives Cand

then, dehydrochlorination leads to a conPugated diene G3

CH3

H3CCH3

S

'

1S> 6'D4D-el2aD3DCare!e

A C DHCl HOD

Treatment of 36ith hydrogen chloride affords 3chloro3"33menthene GE 6hich

then reacted 6ith sodium acetate and acetic acid to give mi(ed GcisGtrans *ulegol

esters GF via allylic dis*lacements Hydrolysis of F affords G33cis and GL3trans3

*ulegol G;@ecause the a1solute configuration of C3% is fi(ed in this system, reduction of

either *ulegol isomer *rovides menthol isomers 6hich can 1e readily e4uili1rated

to *redominently G33menthol

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, #"


54/92



DHCl

7 9 :AcONa

AcOH

HOD H2

CH3

HO

DDMe!,"l

-rite do6n the structural formulae of the com*ounds /to ;

Problem 2". Cefalotin

Cefalos*orin is a Y3lactam grou* anti1iotic Cefalotin, a derivative of

cefalos*orin, has stronger activities on gram G3 and gram GL 1ateria, 1ut lo6er

to(icity Therefore, it has 1een studied and a**lied into medical treatment

Cefalotin has 1een synthesiAed from D3cistein according to the follo6ing diagram:

Chemistry The flavor of life #!


55/92



H2N

HO2C

H

SH

ace"!eB

C6H11NO2S

B#OH

COCl2DC

CH2N2

C11H19NO4S C12H21NO4S

E

C16H27N3O8S

N

N

MeO2C

CO2Me P(OAc4

NaOAc> MeOHF

C12H21NO5S

MeOSO2Cl

NaN3G

C12H20N4O4S

AlHgH

AlODiB#3I

C11H18N2O3S

K

C18H23Cl3N2O7S

CHCO2CH2CCl3OHC

OHC

CF3CO2HL

C10H9Cl3N2O4S

M

S CH2COCl B2H6N

Ac2OO

Pri-i!eP

$!

AcOH

N

S

O

NH

O

S

CO2H

CH2OAc

Ceal"i!

1 Com*lete the a1ove synthetic scheme

2 -rite do6n a reaction mechanism from =to


56/92



of three hydraAides G8C/NHNH) fromlevulic acid in 6hich 8 is one of

the follo6ings:

Com*ound / Com*ound B Com*ound C

/ssmin@ that yo ha$eA inor@ani hemials" le$li aid" other ayli

or@ani omponds" benene deri$ati$es (PhC%O" P%C," -

O2C6%4,Oa)" atalysts (piperidine" +sO%)" and sol$ents

1rovide the synthetic scheme to o1tain / -hat is the *ur*ose of %,"3dio(olan

formationR -rite do6n the reaction e4uation to *re*are Ts/H from toluene

2rovide the synthetic scheme to o1tain B -hat is the reation mechanism using

hNCSR -rite do6n the reaction e4uation to synthesiAe hNCS from alinineR

rovide the synthetic scheme to o1tain C -hat is the role of "3/)NC$H!S/"NaR

-rite do6n the reaction e4uation to *re*are "3/)NC$H!S/"Na from 1enAene

Using signals from *roton nuclear magnetic resonance s*ectrosco*y to *rove that

the reaction 6ith "3/)NC$H!S/"Na has occurredR

4 The three hydraAines G/, B, and C are reacted 6ith hCH/ to generate

corres*onding *roducts GE" F, and ; ;ra6 a common reaction mechanism for

these transformations .f !3N/)C$H!CH/ or !3Me)NC$H!CH/ 6as used instead of

hCH/, should the reactions *roceed more difficult or easierR

Problem 2'. *otus

Dotus is no6n as the scientific

name of eumbo nuciera 8ecently,

Chemistry The flavor of life #$


57/92



Vietnamese researchers colla1orating 6ith Canadian scientists discovered the

a1ility to *romote the *roduction of insuline in Y cells of nuciferine, 6hich may 1e

used to treat the %ypo@lyemia G Hoa Nguyen, H;ien ham, @D 7regoire

Nyom1a et al D+ o 3thnoharmacoo$y, 2012, 142, 4884B


58/92



NH

NH) 8CH/, HL, t

o

NH

NH

8

The reaction scheme for the synthesis of nuciferine is:

,tep 1: Synthesis of3metho(ycar1onyl amine

Me/

Me/

CH/Ga"

Me/

Me/

NHC//Me

CH"N/)

5c/NH!

5c/H

/1

GC%0

H%%

/!N

Di5lH!TH'

0o

C

/2

GC%0H%#/)N

G/

,tep 2: Synthesis of arylacetaldehyde

CH/

@r

G1"

@r

CH/GB

CH"N/)

5c/NH!5c/H

B1

GCH$/)N@r

B2

GCH/)N@r

Na@H!

CH)Cl)

,tep : Synthesis of nuciferine

NMe

Me/

Me//L BDi5lH!

TH'

C1

GC)0H))/!N@r3H@r

C2

GC)0H)%/!N

@'"3/Et)

CH)Cl)OCHCl"G%:%

AlBN,

@u"SnH

Nuciferine

1 ;etermine the structural formulae for /1,/2,B1,B2, 1, 2, reaction conditions

for Ga", G1" and com*lete the a1ove reaction scheme

Chemistry The flavor of life #


59/92



2 .ndicate the reaction mechanism for the formation of /1 from ",!3

dimetho(y1enAaldehyde Gste* %& 1from /L BGste* "

;etermine the structural formulae for t6o isomers of D1a,D1band com*ound D2

1ased on the schematic conversion 1elo6:

Nuciferine% CH". e(cessO5g)/

) Heated

D2

GC)0H)%/"N

CHCl", Na/H #0

@u!NCl

D1a

GC)0H)"/)N

D1bL

Problem 2(. % pectra

1 5t room tem*erature, the NM8 s*ectrum of cyclohe(ane sho6s only a single

resonance *ea 5s the tem*erature of the sam*le is lo6ered, the shar* single *ea

1roadens until at 3$%0 pC it 1egins to s*lit into t6o 1roaden *eas 5s the

tem*erature is lo6ered further to 30 pC, each of the t6o 1ands 1egins to give a

s*litting *attern of its o6n E(*lain the origin of these t6o families of 1ands

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, #


60/92



H

H

H

H

H

H

HH

H

H

H

H

2 .n cis3%31romo3!3tert31utylcyclohe(ane, the *roton on car1on3! is found to give

resonance at !"" **m .n the trans isomer, the resonance of the C!hydrogen is at

"$" **m -hy do these com*ounds have different chemical shift values for the

C! hydrogenR 2ustify 6hy this difference cannot 1e o1served in the !3

1romomethylcyclohe(anes e(ce*t at very lo6 tem*eratures

Problem 2). /% spectra

1Su1stitution of an amino grou* on the ara*osition of aceto*henone shifts the

C=/ fre4uency from a1out %$# to %$#) cmX%, 6hereas a nitro grou* attached to

theara*osition yields a C=/ fre4uency of %$" cmX% E(*lain the shift for each

su1stituent from the %$# cmX%1ase value for aceto*henone

2ConPugation of a C=C dou1le 1ond 6ith either a car1onyl grou* or another

dou1le 1ond *rovides the multi*le 1ond 6ith more single31ond character Gthrough

resonance, as the follo6ing e(am*le sho6s, a lo6er force constant K, and thus a

Chemistry The flavor of life $0


61/92



lo6er fre4uency of vi1ration 'or e(am*le, the vinyl dou1le 1ond in styrene gives

an a1sor*tion 1and at %$"0 cmX% Esters sho6 a very strong 1and for the C=/

grou* that a**ears in the range of %9#0?%9"# cmX%for sim*le ali*hatic esters The

C=/ 1and is shifted to lo6er fre4uencies 6hen it is conPugated to a C=C or *henyl

grou* Gint!

K

c)

%= , H, reduced massI c, seed o i$ht)+

5ssign a structure to each of the s*ectra sho6n Choose from the follo6ing #3

car1on esters

!$th.Ch/ re*aratory ro1lems, Hanoi, Vietnam, 2uly )0%!, $%


62/92



Chemistry The flavor of life $)


63/92



Part 2. P%ACT)CA* P%(+*',-+%E ,/FE+D #


64/92



Problem 3+. Condensation between ?anillin and ben0ylamine

1 Introdtion

&anillinis a *henolic aldehyde 6ith the molecular formula CH/" Thus, it has

three ty*es of functional grou*s including aldehyde, ether, and *henol This

com*ound is often used as a flavoring agent in foods, 1everages, and

*harmaceuticals Vanillin is the *rimary com*onent of the e(tract of

the aniaanioia .t is no6n that the aldehyde functional grou* in vanillin

can 1e easily converted into enamine derivatives or imides through the

condensation reaction 1et6een vanillin and amines The *roducts are synthones

6hich are 6idely a**lied in the synthetic organic chemistry and *harmaceuticals

2 Chemials and #ea@ents

3 Vanillin: %3) g

3 @enAylamine,

3 ;ichloromethane: )0 mD,

3 Sodium sulfate, Na)S/!

Eipment and ;lass'are

3 Erlenmeyer flass, )#0 mD

3 7raduated cylinders, %0, )#, #0 mD

Chemistry The flavor of life $!


65/92



3 @eral *i*ets,

3 @eaers, #0 mD,

3 Hot *late,

3 S*atulas,

3 @chner funnel 6ith filter flas and filter *a*er, se*arating funnel

3 Melting *oint a**aratus and ca*illary tu1es,

3 Small vials 6ith ca*s,

3 Vials 6ith ca*s, )0 mD

3 Thin layered chromatogra*hy GTDC s*otters,

3 TDC *lates Gsilica 6ith fluorescent indicator 5)#!,

3 Cham1er for TDC develo*ment,

3 Magnetic stirrer,

3 .ce 6ater 1ath

4 EGperimental proedre

1 5dd %0 g of vanillin into a dry #03mD flas then add %0 mD of dichloromethanesolvent into the flas The mi(ture is stirred for %0 min at room tem*erature, and

then 09 g of 1enAylamine and )0 g of Na)S/!are simultaneously added into the

flas

2 The reaction mi(ture is further stirred at reflu( condition G$#3$9 oC for 0 min

Cool the flas to room tem*erature

;ilute the resultant mi(ture 6ith !0 mD and s6irl the flas

4 Transfer the mi(ture into a se*arating funnel and then e(tract 6ith "0 mD of

dichloromethane E(tract the organic *hase ) times more 6ith "0 mD of

dichloromethane

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;ry the e(tracting organic fraction 6ith MgS/! 'ilter the organic

fraction through a @uchner funnel ;iscard the solid and collect the filtrate

68emove the solvent in the filtrate 1y rotary eva*oration to o1tain the *roductGs

:;etermine the *urity of the crude *roduct 1y thin layer chromatogra*hy method

Use *recoated silica gel *lates GSilica 7el '3)#! and visualiAe the s*ots 1y UV3

light Use ethyl acetate: he*tane %#:# mi(ture as an eluent

Note:#t is recommended to carry out the e9eriment under a hood+

>estions and 3ata analysisA

% -eight the o1tained *roduct

) ;ra6 the mechanism of imine formation

" -hat is the role of Na)S/!in the *resent e(*erimentR

Problem 31. ynt&esis of eugeno!y acetic acid

1 Introdtion

Eugeno(yacetic acid G.U5C name: )3metho(y3!3G)3*ro*enyl*heno(yacetic

is an odorless, colorless and non3cytoto(ic com*ound .t has sho6n anti3viral and

anti31acteria *ro*erties and is therefore used as antio(idant food *reservative in

food industry 8ecently, eugeno(yactetic acid and its ester derivatives such as

methyl and ethyl esters have 1een found to 1e the a1ility to inhi1it li*id increasing

6hich leads to their *otential a**lication in the treatment of humanhy*erli*idaemia .n addition, eugeno(yacetic acid acts as a *romising *lant gro6th

*romoter due to their au(in Garylo(yacetic structural characteristics

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The nature and living organism friendly *ro*erties of eugeno(yacetic are the result

of the com1ination of acetic moiety 6hich is *resent in vinegar and eugenol moiety

6hich is the main constituent of the essential oil o1tained from clove oil

Clove is an aromatic *lant in the family Damiaceae 6hich is native to tro*ical areas

and 6ides*read as a cultivated *lant .n Vietnam, there are t6o s*ecies of clove,

%cimum sanctumD and %cimum $ratissimumD, 6hich have 1een used in many

tradtional medicinal *ur*oses 6ithout adverse effects

.n this *ractical *ro1lem, eugeno(yacetic acid 6ill 1e synthesiAed from eugenol

as sho6n in the scheme 1elo6:

2 Chemials and apparats

3 Clove essential oil,

3 Monochloroacetic acid,

3 Na/H,

3 Na)C/"

3 54ueous HCl solution,

3 ;istilled 6ater

/pparats and @lass'are

3 Erlenmayer flas: #0 mD,

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3 Magnetic stirrer 6ith heater,

3 Magnetic 1ar,

3 @eaer: %00 mD,

3 @eaer: )#0 mD,

3 7lass filter: )# mD,

3 7lass filter: #0 mD,

3 Vacuum filter set Gvacuum *um*, 'ilter flas,

3 ;ro**ing funnel,

3 S*atula,

3 7lass rode,

4 EGperimental proedreA

,tep 1

1 ;issolve 0$ g Na/H in "0 ml distilled 6ater in a #0 mD3Erlenmayer flas and

then add )0 mD clove essential oil ee* the flas in the 6ater 1ath at 030 oC

6hile stirring 6ith the magnetic stirrer

2 ;issolve carefully %0 g monochloroacetic acid in #0 mD distilled 6ater in a )#

mD 1eaer& stir the solution 6ith the s*atula 5dd Na)C/" slo6ly Pust to thealaline reaction GSolution /

,tep 2

1 5dd slo6ly the solution /to an Erlenmayer flas and ee* stirring the mi(ture

at 03# oC for $0 min Cool the reaction mi(ture 6ith 6ater to room tem*erature,

and then acidify 6ith HCl %:% to the acidic reaction Gtest by itmus aer GSolution B

2 5dd a small amount of crushed ice G#3%0 g to the solution @ and stir until the

yello6 oil turns to the solid .solate the solid 1y filtration 6ith suction in to asintered glass cruci1le -ash the solid 6ith 6ater to o1tain the crude *roduct as

*ale yello6 solid

,tep

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1 urify the *roduct as follo6s: transfer the crude *roduct to a )#0 mD 1eaer, add

03%00 mD hot 6ater Ga1out 0 oC to the 1eaer and continue 1oiling for #3%0

min Cool the solution 6ith 6ater and ice3cold 6ater

2 .solate the *roduct 1y filtering 6ith suction into a sintered glass cruci1le and

6ash the solid several times to o1tain 6hite needles ;ry the solid in the drying

oven for $0 min -eigh the dried *roduct

>estions and data analysisA

% -rite do6n the reactions occurring in ste* %a, %1 and )

) Calculate the reaction yield

" ro*ose a mechanism for the re

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02 18 2014 IChO46 Preparatory Problems