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ORGANIC CHEMISTRY
CHP2 : HYDROCARBON
ALKENE
Prepared By:
ARBANAH MUHAMMAD
CLD 10302
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TOPIC COVERED
Alkenes
Nomenclature of Alkenes
Naming of Cycloalkenes
Geometric Isomers
Properties of Alkenes
Syntesis of Alkenes
Principal Reactions of Alkenes
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Introduction
Classifcation oHydrocarbon
Hydrocarbon
Aliphatic Aromatic
Alkanes Alkenes Alkynes
Cycloalkanes
Cycloalkenes
Saturated
Unsaturated
http://c/Documents%20and%20Settings/user/Desktop/alkanes%20copyright%20reserved.ppt#-1,3,Slide%203http://c/Documents%20and%20Settings/user/Desktop/alkanes%20copyright%20reserved.ppt#-1,4,Slide%204http://c/Documents%20and%20Settings/user/Desktop/alkanes%20copyright%20reserved.ppt#-1,4,Slide%204http://c/Documents%20and%20Settings/user/Desktop/alkanes%20copyright%20reserved.ppt#-1,3,Slide%2037/24/2019 Ch2 Hydrocarbon _alkene
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Hydrocarbons
Hydrocarbons
Alipatic
Alipatic
Alkenes
Alkenes
Alkenes are
y!rocar"ons tatcontain a car"on#car"on
double"on!$
C C
% %
% %
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Hydrocarbons
Hydrocarbons
Alipatic
Alipatic
CycloAlkenes
CycloAlkenes
Alkenes &ose car"on
atoms are 'oine! inrings$
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Unsaturatedhydrocarbon
General formula
Aliphatichydrocarbons
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C(C)OA)*ENES
Alkenes whose carbon atoms are joined in
rings
General formula CnH2n-2 where n =3,4,5..Eg:
Cyclopentene, C5H
Cyclobutene, C!H"
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CH3 CH3
1,3- diethylcyclopentene
E#G $: Cycloalkene with substituents
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Naming Alkenes
!e ust account "or dou#le #ond$
1. %ongest chain must contain the double bond % & '
(# )umber of carbons so that the dou#le #ond has the
lo&est nu#er
*# +ndicate the positionof the double bond
!# Change ending to' ene5# se the same rules for the substituent %side chains and
halides'
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-he ending of the alkenes with more than one
double bond should be change from -eneto:
diene' if there are two double bonds
triene. if there are three double bonds
1,3-butadiene
1,3,5-heptatriene
CH
(
CH
*
CH(
$
CH(
!
CH(
$
CH
(
CH
*
CH
!
CH
5
CH
"
CH*
/
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+, Replace te #aneen!ing of te cycloalkane
a-ing te same num"er of car"ons "y #ene$
., Num"er throughte !ou"le "on!in te!irection tat gives the lower numberto te
firstappearing substituent$
/#Etyl#+#metylcycloe0eneC%1
C%.
C%1
+
.1
2
3 /
E$G .4 Naming cycloalkenes
(irst appearing
su#stituent at dou#le
#ond
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)umber substituted cycloalkenes in the way that gi)es the
car#on atos o" the dou#le #ond the 1 and 2 positions.
-hat also gi0es the substituent groups the lo&er nu#ers
at
the "irst point o" di""erence.
1-ethylcyclopentene 3,5-diethylcyclohe*ene
5
$
!
(
*
CH*
.
1
+
2
/
3
C%1C%1
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Geometric Isomer
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Trigonal planar
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.#"utene
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Alkenes nomenclature must specify &eter a
gi-en molecule iscis ortransif it is a
geometric isomer
Eg +44
CH3
C = C
CH3
HH
cis-2-#utene
1arger group
on the sameside
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CH3CH2
C = C
H
CH2CH3H
trans-3-he*ene
1arger group
on the
different side
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CH3CH2
C = C
CH2CH3
CH2CH2CH3H
trans-4- ethyl '3-heptene
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CH3CH2
C = C
CH2CH2CH3
CH3H
cis-4-ethyl-3-heptene
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Howe0er, Cis . trans stereoisoeris +geoetry
isoer in alkenes is not possible when :
one of the doubly bonded carbons bears t&o identical
substituents
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Using the prefx E ndZ
Altoug te prefi0es cis an! trans can "e use! to
!istinguis !isastereomers &en t&o alkyl groups are
"on!e! to te C C 5 tey cannot "e use!&en tere
are three or four al!yl groups "on!e! to te C C$
A completely unam"iguous system for specifying
!ou"le "on! stereocemistry as "een a!opte! "y te
I6PAC "ase! on an atomic num"er criterion for
ranking su"stituents on te !ou"ly "on!e! car"ons$
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2hen atoms of higher atomic numberare on the sae side o"dou#le #ond, we say that the double bond has the Zconfiguration#
2hen atoms of higher atomic numberare on opposite site o"dou#le #ond, we say that the double bond has the Econfiguration#
HigherHigher
1ower 1ower
1ower
1ower
Higher
Higher
3 4efer to page $ in our te6t book
C C
%
7r
8
C+
C C
H
8
7r
C+
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!h"sic#!roperties
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Physical Properties
9imilar to alkanes
olu#ility
1ow density, #oiling point and elting point
roperties 0ary based on chain sie
+nteresting physical properties
Alkenes with se0eral double bonds will ha0e a color
associated &ith the
9oluble in non polar sol0ent
)ot soluble in water
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Colore! Alkenes
1;C
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hysical roperties of Alkenes
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Syntesis of alkenes
#Dey!rogenation
#Dey!ration#Dealogenation
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7 (
Dey!rogenation of alkanes47 8 ( 8 %
Dey!ration of alcools4
7 8 %9 ( 8 O%
Dey!roalogenation of alkyl ali!es4
7 8 %9 ( 8 :r5 Cl
C CC C ; 7 (
Syntesis of alkenes4 Elimination reactions
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Elimination of molecule %.
limite! to in!ustrial syntesis of etylene5 propene
C; %.
Syntesis ofalkenes
Dehydrogenation of al!anes
% % C CC C ; %.
E0ample
etene ?etylene,etane
% %C C
%%
%%C C
%
%
%
%
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%.SO2
+/=>C; %.O
Dehydration of al"ohol
)oss of % an! O% from a!'acent car"ons$ Aci! catalyst is necessary$
% O% C CC C ; %.O
E0ample
Syntesis ofalkenes
etanol
% O%C C
%%
%%
etene ?etylene,
C C
%
%
%
%
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+= @ #$ %
H&'()
*$+,;
A reaction tat can procee! in more tan one!irection5 "ut in whi"h one dire"tion
predominates- is sai! to "e regioselecti-e$
Regiosele"tivity in al"ohol dehydration
.#metyl#.#"utanol .#metyl#+#"utene .#metyl#.#"utene
Syntesis of alkenes
,
,
, ,
(H
,H
H
H
H
H
H
H
H
H
H
H ,
,
, ,,H
H
H
H
H
H
H
H
H
H ,
,
, ,,H
H
H
H
H
HH
H
H
H
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en elimination can occur in more tan one!irection5 te principal alkene is te one forme!
"y loss of %from te car"on a-ing te
fe&est y!rogens$R O%
C%1
C C
%
R C%.R
Baitse- Rule
.% on tis car"on
R
R
C%.R
C%1
C C
only +% on tis car"on
Syntesisof alkenes
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Dey!roalogenation of alkyl ali!es
1oss of H and halogen %>' from an alkyl halide +n the presence of strong base in sol0ent likewise
)a
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Reaction of Alkenes
rimarily reactions in0ol0e the double bond
-he key reaction of double bond is addition reaction
%7reaking the bond and adding something to each carbon'
A - /
A /
-he major alkene reactions include additions of hydrogen
%H2',halogen % C62or /r2', water %HH' or hydrogen
halides %H/r or HC6'
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REACTION O A)*ENE
H.DR(/0NA12(N
H.DRA12(NH.DR(HA3(/0NA12(N
HA3(/0NA12(N
(4(N(3.'2'
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Rea"tion of Al!enes
1. Hydrogenation ' Addition o" H2
Addition of a molecule of H(
4esults in the formation of an alkane
sually re@uires heat, pressure and a catalyst like t, d or )i
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Rea"tion of Al!enes
2. Hydration$ Addition o" H2
-he addition of water to an alkene
produces an alcohol
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Rea"tion of Al!enes
R i f Al!
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Rea"tion of Al!enes
R ti f Al!
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Rea"tion of Al!enes
R ti f Al!
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Rea"tion of Al!enes
3. Hydrohalogenation
Addition of H>to an alkene
H> . H8, HC+, H7r, H+
+t follows arkoniko0Bs rule where the H ends up on the
carbon with the most hydrogen to start with
R ti f Al!
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Rea"tion of Al!enes
R ti f lk
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Reactions of alkenes
)5 Halogenation: Addition of 6&
Te a!!ition of alogen to an alkene
pro!uces a aloalkane or alkyl ali!e
Simple la"oratory test for unsaturation$
C C 7.R R RCCR
77
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3$ Oonolysis of alkenes
+st step # reaction of alkene &it oone to form
ozonide.
.n! step # y!rolysis of ooni!e to form al!ey!e
an! ketone$
; O1C C
O
O O
C C
C O CO;
%.O5 Bn
R RF
R
R
%
%
RF
R
ooni!e
al!ey!e ketone
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