Ch2 Hydrocarbon _alkene

7/24/2019 Ch2 Hydrocarbon _alkene

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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
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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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Ch2 Hydrocarbon _alkene

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