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Stereoisomerism
Optical isomerism
Plane polarized light
Condition for optical activity: -
The necessary condition for a compound to exhibit optical activity is that it should be asymmetric or
dissymmetric and geometric structure of the molecule should not super-imposable on its mirror
image. Further it should not contain any of the following elements of symmetry.
Elements of symmetry
Plane of symmetry: -
plane which divides the molecules into e!ual and identical halves which are super imposable mirror
images of each other.
These compound are called meso and optically inactive.
a
b
b
c
a
c
2. Centre of symmetry: -"t is an imaginary point in the centre of molecule from which if lines are
drawn on any group# on both the sides two and e!ual distance then it divides the molecules into two
e!ual halves which are mirror images of each other.
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C C
CC
H
COOH
H
COOH
H
COOHCOOH
H
3. Alternating axis of symmetry: -
"t should posses one or more chiral carbon atom.
$ight direction% - dextro rotatory &'( &d(
)eft direction% - )eavo rotatory &-( &)(
*xample of optically active compound
1. +ontaining one chiral +-atom% -
OH C
COOH
CH3
H H C
COOH
CH3
OH
$acimic ,ixture% - n e!uilibrium mixture of dextro-rotatory )ebo rotary. "t is optically inactive.
. /hat is optical isomerism0
Show optical isomer of lactic acid.
2. Containing two chiral c-atom: -
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OH
OHC
C
COOH
H
COOH
H H
HC
C
COOH
OH
COOH
OH H
OHC
C
COOH
H
COOH
OH
( + d ) T a r t a r i c a c i d ( + l ) T a r t a r i c a c i d m e s o T a r t a r i c a c i d
Enantiomer and diasteromers: -
*nantiomers are the optically active compound having no super imposable mirror images.
1iastereomers are optically inactive compound which are not mirror images of each other.
OH
Br
CH3
H
CH3
H H
H
CH3
Br
CH3
OH
( + ) d 1 ( - ) l 2
H
Br
CH3
H
CH3
OH OH
H
CH3
Br
CH3
H
( + ) d 3 ( - ) l 4
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+ompound 2 3# 4 5 are enantiomer.
+ompound 2 4# 3 5 are diastereomers
Only one +hiral +-atom present then no existing diasteromers.
The physical or chemical properties of enantiomer same except% - the angle of rotation toward left or
right.
The physical properties of diastereomer are di6erent and the chemical properties are similar but not
identical.
peci!c rotation: -
The measurement of optical activity is denoted in terms of speci7c rotation. "t is constant for a
compound and is the characteristic properties.
The observed angle of rotation produces by a solution of concentration 2gm8ml ta9en in a tube of
length 2dm &cm(
"#estion: -:ive the example of no carbon chiral atom
$ptical activity witho#t chirality:-
llene derivatives% -
*xample% 2# 4- diphenyl propadiene
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H5C6
C C C
C6H5H
H H
C C C
HH5C6
C6H5
*xp% - "n allene the central carbon is s-p hybridized and the terminal carbon are Sp3 carbohydradized.
The +entral carbon forms two Sp-Sp sigma covalent bonds. The central carbon also has p-orbitals
which are mutually perpendicular and form pi bond with the terminal carbon. s a result the
substituent of one end the molecule is perpendicular to the other. So the compound exists in two
forms which are non super-imposable mirror images. ;ence they are optically active.
3. %iphenyl derivates: -
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3. Presence of bul9y groups at ortho position which prevents the free rotation of two benzene
rings. Therefore the molecular wire prefers a conformation in which rings will be perpendicular
to each other and if it will be devoid of elements of symmetry. /hen both the double bond of
allene are replaced4. Spirans by rings the resulting compound is 9nown as spiro compound or spirans
The double bond may be replaced by 5# > or ? member ring. The two replaced rings areperpendicular to each other and hence substrate ' attaching reagent- product
bC
CH2
C
CH2
Ca
CH2 CH2ba
aC
CH2
C
CH2
Cb
CH2 CH2ab
#&stit#tion reaction: -
The replacement of an atom or group directly attached to carbon in the substrate molecule byanother atom or group is called substitution reaction.
CH3OH + HBr CH3Br + H2O
+ Br2
Br
+ HBr
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'#cleophic s#&stit#tion reaction (' reaction): - Substitution reaction brought about by
nucleophiles is 9nown as nucleophic substitution.
Three parts% - Substrate# =u# Solvent
Substrate% l9yl group# leaving group
,echanism% - S=2and S=3
S=2% @nimolecular reaction#
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S=3%
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CH3 C
CH3
CH3
BrS l o w
CH3 C+
CH3
CH3
Br-+
Step 3
CH3 C+
CH3
CH3
OH -
+ CH3 C
CH3
CH3
OH : OH C
CH3
CH3
CH3
5 0 5 0 ! a c i m i c " i # t $ r e
F a s t
:
tero-chemistry of '1 *echanism
S=2mechanism leads to retention of con7guration and form a racimic mixture
'2 *echanism
C % ++ & C & %
/hen rate of the reaction is proportional to the concentration of substrate as well as nucleophlic # the
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reaction proceeds by a S=3 mechanism.
*echanism: -"t is a one step reaction in which the nucleophie denotes a pair of electrons to the
group# simultaneously the group withdraws the electron pair through the formation of transitory state.
C % ++ &-
& C % %-
& C
T r a ' s i t i o ' s t a t e ' e r t e d * r o d $ c t
Stero chemistry of S=3 ,echanism
S=3 reaction proceeds via inversion of con7guration and forms the invented product &/alden
inversion(
++ OH -
HO C
H
H
Br
H
Br-
OH C
H
H
H
T r a ' s i t i o ' s t a t e ' e r t e d * r o d $ c t
CH3 Br
uestion% - /hy S=3- -reaction gives a inverted product% - due to bac9 side attac9.
S=2 S=3
@nimolecular
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Energy pro!le diagram
'1
:raph
'2
:raph
'arreaction: -('#cleophilic s#&stit#tion reaction in orgomatic system)
The reactions do not occur easily in halogens because +-B bond in heloal9enes. lso the low pair ofelectron in halogens participates in delocalozation with the pi electron of benzene rings. 1rastic
condition such as high temperature high pressure and highly concentrated reagents are used to carry
out =ucleophilic substitution in hello--- The reaction follows elimination addition mechanism via the
formation of intermediate benzyne.
Cl
+ aH 2 aClH i g h t e m p e r a t u r e p r o c e s s
N H3
H2
+
, ' i l i ' e
*echanism of this reaction: -
The reaction ta9e place in two steps% -
tep 1: -The elimination reaction with the formation of benzyne intermediate.
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Cl
H
+ H2- + H3 + Cl
-
B e ' . ' e i ' t e r m e d i a t e
Step 3% - ddition reaction ta9es place% -
+ H3H2
H
Or
+ H3
H2
H
Electrophilic orometic s#&stit#tion reaction: -
/hen substitution occurs in the benzene ring due to the attac9 of an electrophils is called elctrophilic
aromatic substitution reaction.
+ %-
/
+/ %
/ l e c t r o * i l i c r e a e ' t
,echanism% -
tep 1: -Formation of an electrophile
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/ %C a t a l y s t
%-+/
+
/ l e c t r o * i l e
tep 2: - *lectrophile attac9s on bezene ring to form a carbocation intermediate
+
/H
+
/H
+
/H
+
/H
+/
+
C a r b o c a t i o '
tep: 3The carbocation loses a proton to the base to form the 7nal substitution product.
i ' a l * r o d $ c t
/H
+ + %-
/
*xample% - Friedel craft reaction# ;elogination# sulphonation# nitration
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+riedal carft reaction
The reaction in which benzene reacts with al9yle8acylhalide in the presence of catalyst l+l4to form
al9yl8acyl benzene
l9ylation% l9yl halide
+ CH3Cl + ,lCl3
CH3
+ HCl
" e t . l c l o r i d e
,echanism% -
Step 2% -
Step 3
+
CH3H
+
CH3H
+
CH3H
+ CH3Cl
CH3H
+ C a r b o c a t i o n
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Step 4% -
CH3H
+ + ,lCl4-
CH3
+ HCl ,lCl3+
Acylation: -Acylhalide
+ CH3OCl ,lCl3+
COCH3
+ HCl ,lCl3+
Step 2% -
CH3OCl ,lCl3+ CH3CO+
+ ,lCl4-
Step 3% -
CH3CO+
+
CH3COH
+
Step 4
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CH3COH
+ + ,lCl4-
CH3CO
+ HCl ,lCl3+
,alogenation
+
Cl
+ HCl ,lCl3+Cl ClA l C l
3/ F e C l
3
Step 2
Cl Cl + ,lCl3 + ,lCl4-
Cl+
C l o r i ' i $ m i o '
Step 3
+ Cl+
H Cl
+
+
CH3H
+
CH3H
+
CH3H
Step 4
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H Cl
+ + ,lCl4-
Cl
+ HCl ,lCl3+
'itration: -
+ HO 3
O2
+ H2O H2SO4+C o n c . H
2S O
4
tep 1: -
HO 3 + 2H2SO4 O2+
+ H3O+
+ 2HSO 4-
tep 2: -
+ O2+
+
O2H
+
O2H
+
O2H
O2H
+
tep 3: -
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O2H
+ + 2HSO4-
O2
+ H2O H2SO4+
Elimination eaction: -*limination reaction involves the removal of two atoms or grows attached to adCacent carbon atom in
a molecule to produce on unsaturated compound. One of the group of atoms commonly eliminated as
proton and other as an anion.
1ehydration of al9yl halide% -
+ + +CH3CH2
CH2
Br OHCH3
CH
CH2Br OH2
, l c o o l i c
+ + +OH % OH2, l c o o l i c
H
C C
%
C C
1ehydration of lcohol
+ OH2C C
OHH
C CH e a t A c i !
,echanism % -There are two types.
E1*echanism: -Two steps and unimolecular.
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Tertiary al9yl halide
Step 2% The substrate undergo heterolysis to from halide anion and carbocation
C C
H
%
H
S l o w+ %
-
C a r b o c a t i o '
H a l i d e i o '
CH4
C+
C
HH
Step 3 The carbocation rapidly loses a proton to base and forms the al9ene.
C+
CH
HH+
B-
C C
HH
+ HB
" a s t
,olecularityD2 &unimolecular(
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C
CH3
CH3 Br
CH3
CH3 C
CH3
CH2
++ OH -
OH2
E2 *echanism: -
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"n dehydrohalogenation hydrogen is eliminated preferentially from the carbon atom which has less
number of hydrogen atoms and so the highly substituted al9ene is the maCor product.
+ OH -
CH3CH2
CHCH3
Br CH3CH2
CHCH2
CH3CH
CH
CH3
1-b$te'e
2-b$te'e
r e e r r e d * r o d $ c t
H e a t
+ OH -
CH2CH2
CH2CH2CH3
Br 2-*e'te'eH e a t CH3CH2
CHCH
CH3
*limination vs. substitution% -
"n the presence of strong bases &lcoholic EO;( the al9yl halide undergo elimination reaction# whereas
a! EO; wea9 bases favor the substitution reaction.
)ess polar solvent at high temperature favor elimination reaction while more polar solvent at lower
temperature favour the substitution.
"#estion: 1ehydration of alcohols &2# 3- elimination(
lcohols are converted into al9enes in dehydration with the removal of water molecule.
$e!uires the presence of an acid heat
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C OH
CH3
CH3
CH3
H e a t H2
S O4
CH3
C CH2
CH3
T e r t i a r . b $ t . l a l c o o l s o b $ t e ' e
*echanism: -
Step 2
Step 3
This protonated alcohol dissociate into carbocation water
Step 4
+arbocation loses a proton on a base
+#el comstion
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+#el: - fuel is any combustible substance containing carbon as main constituent# which on properburning gives large amount of heat which can be utilized economically for domestic and industry
purpose.
Comstion: -ny chemical process followed by the evolution of light and heat is calledcombustion
+lassi7cation of fuel
2. On the basis of occurrencea. =atural &primary fuel(b. rti7cial &secondary fuel# derived fuel(
3. On the basis of their physical statea. Solidb. )i!uidc. :aseous
Solid /ood# coal# biomass# cattle# dung ca9e
+o9e# charcoal
)i!uid fuels 2. =atural% crude oil
3. rti7cial%
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The total !uantity of heat librated from the combustion of a unit mass8unit volume of the fuel in the
presence of air or oxygen
gnition temperat#re: -The mini or lowest temperature at which the fuel must be so pre heated so that it starts burning
easily is called ignition temperature.
"gnition temperature =ormal# moderate
,oisture content% -)owest
=on combustible metal% - ,inimum
+ombustion rate% -moderate
Product of combustion should not be harmful+ombustion should be controllable
)ow storage cost
*asy to transport
"#estion: - +ompare a demerit merit of solid fuel li!uid fuel
Solid Fuel )i!uid fuel :ases fuel+ost +heap They are costly ery costlyStorage *asy They are stored in
closed container)ea9 proof container
+alori7c value )ow"gnitiontemperature
)owest
,oisture ;igh ,ini
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+ombustion rate )ow ;igh ery high+ombustioncontrol
;ard &diGcult( +ontrol regwire *asy and large bystopping gas supply
Calori!c val#e of a f#el: -
;igher calori7c value8gross calori7c value &;+ or :+(
)ower calori7c value8=et calori7c value &=+ or )+(
"mp. The total !uantity of heat liberated or unit volume of the fuel in the presence of air or oxygen#
when product of combustion are allow to coat at room temperature it is called higher calori7c value.
)+ or =+
The total !uantity of heat liberated from the combustion of unit mass &unit volume( of the fuel in thepresence of air or oxygen when products of combustion are allowed to escape.
nit of heat: -
Calorie: -mount of heat re!uired raising the temperature of 2gm of water by one degree
centigrade
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4ilo Calories: -mount of heat re!uired to raise the temperature of 2 9g of water by one degree is
called 9ilo calorie.
%ritish thermal #nit (%..):-
;eat re!uired to raise the temperature of one pound of water by one degree Fahrenheit
Centigrade thermal #nit (C,)
;eat re!uired to raise the temperature of one pound of water of one degree centigrade
uestion% - fuel sample contains H5I carbon# 2.>I sulphur# ?I =3#>.>I hydrogen and rest oxygen.
;+ of the fuel is H.4>? 9cal8gm. +alculate =+
Solution
5etermination of calori!c val#e
*xperimental determination of bomb calorimeter method
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Theoretical calculation of calori7c value by 1ulongs formula
1iagram
6or7ing
bout J.>32 gm of the fuel sample is ta9en and clean the crucible which is then 7tted in bomb.
7ne ,g-gire touching the fuel is than stretched along the electrode.
The bomb lid is tightly screwed and 7lled with oxygen of about 3> to 4- atm pressure.
The bomb is then placed on copper calorimeter containing the 9nown mass of water.The initial temperature of water is noted after through stirring.
The electrodes are then connected to ? battery to complete the circuit.
The fuel sample burns and heat is librated which is transferred to water.
@niform steering of water is continuous and the maximum temperature is attained is noted.
Calc#lation: -
)et xD mass of fuel samples ta9en in the crucible/D ,ass of water ta9en in calorimeter
/D water e!uivalent of apparatus &+alorimeter steerer# thermometer etc# /K x speci7c heat of
apparatus T2 Dinitial temperature
T3D 7nal temperature
;D ;+ of fuel
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Correction: -
To get more accurate results the following correction must be considered while calculating the
calori7c value.
+#se wire correction: -The heat liberated above includes the heat given out by the ignition of fuse
wire used. ;ence it must be subtracted from the total value.
Acid Correction: -Fuel containing sulphur and nitrogen are oxidized under high temperature andpressure of ignition to form ;3SO5 and ;=O4 respectively. The formation of these acid are exothermic
reaction. So the measured heat also include the heat given out during acid formation. "t should be
deduced from the total value.
Cooling correction: -Time ta9en to cool the water in calorimeter from max temperature is noted
from the rate of cooling &dT8min( and actual time ta9en for cooling &t-minutes( the cooling correction
of dTxt is added to rise in temperature.
Cotton thread correction: -The heat liberated from the cotton thread &if use( is deducted.
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"#estion: - sample of coal containing HLI +# HI ;# 4I ash# when tested in liberated for it + in
bomb calorie meter the following data is obtained weight of coal burnt DJ.Hgm# weight of
waterD?>Jgm
ol#tion: -
heoretical calc#lation of calori!c val#e: -
The calori7c value can be of fuel approximate calculated by noting the amount of the constituent of
the fuel
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The ;+ of the chief combustible constituent of a fuel are% -;ydrogen# carbon# suphur
Oxygen if present in the fuel is assumed to be present in combined form with hydrogen &7xed
hydrogen( in the form of . So the amount of hydrogen a variable for combustionD Total mass of
hydrogen in the fuel- 7xed hydrogen
Since H parts of O3combine with 2 parts of ;3to form L parts of water.
uestion% - coal sample contains +DH>I# ;DHI# SD2I# =D3I# ashD5I. +alculate ;+ and =+
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"#estion: -
Comstion: -+alculation of air !uantities
"#estion: -+alculate the weight and volume of air re!uired for the complete combustion of 2Eg
carbon.
$e!uirement of combustion of 29g +
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"#estion: - Fuel sample +DM>I# ,D>.3I# OD23.32I# =D4.3I# ashD5.>I. +alculate the weight ofair re!uired for the complete combustion of 2 9g of the fuel &coal(
+alculation of O3is re!uired
Solution% -
2. +arbon
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3. ;ydrogen
Coal: -+oal is highly carbonaceous &carbon containing ( matter# that has been formed as a result ofalteration of vegetable matter &plants( under certain favorable condition. "t is composed of carbon
hydrogen nitrogen and oxygen with some other non combustible inorganic metals.
Classi!cation of coal &y ran7
arious types of coal are commonly categorized on the commonly the basis of ran9 of degree of
alteration or coali7cation on the wood.
The process of formation of wood is called coali7cation.
Progressive transformation of wood to anthracite
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5ecrease properties: -
,oisture content# ;ydrogen# =itrogen# Sulphur# Oxygen content# volatile matter
ncrease: -+arbon content# +alori7c value
)ignite% -"t is called brown coal soft and lowest ran9 coal# soft and lowest ran9 coal
%it#mino#s: -+ommon coal
Pitch bac9 to dar9 gray
+arbon% HJ-LJI
,oisture% + N H33-H>JJ 9cal89g
Anthracite: highest ran9 coal below 2JI moisture
L3-LHI weight
)owest moister and volatile matter hardest of all 9ind of coal
Analysis of coal: -
Proximate analysis: -to determine the !uality of coal
*oist#re: -bout 29g coal &7nely produced form ( &air dried( and weighed in crucible &silica(
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8olatile *atter: -
Car&on
Car&on 9,ydrogen: -bout 2-3 gm accurately weighed coal sample is burnt in the presence ofoxygen in a combustion apparatus condition ; of the coal are converted into +O3 and ;3O
respectivelyThese gaseous products of combustion are absorbed respectively in EO and anhydrous +a+l tubes of
9nown weight. The increase in weight determines the amount of carbon of hydrogen.
=itrogen- 9Ceidene ,ethod
bout 2 gm of accurately weighed produced cool is heated with concentrated ;3SO5.
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Conformation: -
The di6erent arrangements of atoms or groups in space which can be converted into one another by
rotation about +-+ single band in a molecule are called conformation.
*xample% +onformation of ethane
=ewmann proCection formula% -
.&dot( shows the bac9 carbon
6)ines emerging from dot# one substituent of bac9 carbon
+ircle% - shows the front carbon
)ine emerging from the circumference of the circle or the constituent of front carbon
Staggered conformation% -
,ore stable# less energy
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H
HH
H
H H
$otation by ?Jo
HH
HH
HH
&*clipsed conformation(
4?Jorotation we get ? conformation three staggered and three eclipsed
+onformation of n-butane% - H
C C
HH
CH3
H
CH3
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H CH
3
H CH
3
H
H
H
H
H
HH
HH
CH3
H CH
3
HH
HH
H CH
3 H CH
3
H
HH
H
H CH
3
H
HH
H
H CH
3H
CH3
H CH
3
H
H
HH
$ %o
$ %o
$ %o
$ %o
7 S t a g a r e d * . * c l i p s e d F S t a g g a r e d
. * c l i p s e d < S t a g g a r e d
CH3H
CH3H
HH$ %
o
+ . * c l i p s e d
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:eometrical isomerism% - ;inged rotation of +D+ double bond
C C
b
a
b
a
C C
a
a
b
b
C i s T r a ' s
*ach doubly bonded carbon di6erent atom functional group
*-Q =otation% -
1ecided the priority of each doubly bonded carbon &using cahn invgold prelog priority rules( se!uence
rule.
"f similar priority are on the similar side of the double bond than the compound- Q isomer &cis(
"f similar priority are on the opposite side of the double bond than the compound *- isomer &trans(
Q% - Qussasmein &on same side(
*% -*ntigen &on opposite side(