Alkene and Alkyne mechanisms

Page # 1
Addition of H-X to an Alkene - Electrophilic Addition Reaction

Possibility # 1



H H
H
protonation CHz cuz
H C H
C C notformed toounstable
H




1
H H

Possibility # 2

H
As
Br
protonation




Regioselective:
YES macroknominksoninionaleisomer
at
aurea
Stereoselective: NO
nucleophilic Br
Carbocation Rearrangement: YES attack

Reaction Summary:
Haloalkehl
Step1 PROTONATION
It goes to carbon of doublebond with mostprotons
NUCLEOPHILIC ATTACK
step 2
aBoor
x goestothemostcarbocation like carbocation followingcarbocation
rearrangement it necessary I
the halogengetsadded on to the more substitutedcarbon
Product




Example:



+ HCl
Cl I

, Page # 2
Acid Catalyzed Hydration of an Alkene
O H O


H O S O H
n
+ O proton
O + O S O H
H H transfer
O
UN H H
O



H

H C H protonation so H2O
C C
H


I
H H


H

GO nucleophilic
H H attack H O H

nucleophile



Alcohol


oo H H
iOH H O H I
O
deprotonation
I Oxonium
ion
Product


Reaction Summary:
Step 1 protonation of alkene to generate more stable
electrophilic carbocation
moleculeon
Step 2 attackof thenucleophilicH2O
createsan oxoniumion
Regioselectivity:
YES Markovnikov
alcohol
step3 deprotonation by abasegeneratesthe
OILGOESONMORE SUBSTITUTEDCARBON
FOLLOWSMARKOVNIKOV Stereoselectivity:NO racemic mixture
RACEMICMIXTURE FORMED IF THERE'S ACHIRALCENTER
Example: Carbocation Rearrangement:YES
OH
Cat H 2SO 4
N
H 2O racemic

, Acid Catalyzed Addition of an Alcohol to an Alkene Page # 3

H O

H O
O
S O H
n
+ H 3C O H H 3C O H O S O H

O O

CH 3 H
C O
H 3C CH2 H CH 3
H CHz

U

H 3C
I O H
monaonenaiti




Ester

H 3C O H
y CH3
A
deprotonan.ona
µy
f
Product



Regioselectivity: YES Markovnikov

Steroselectivity: NO Nh proceeds via planarcarbocation

Carbocation Rearrangement: YES
REMOVE AN H FROM THEACID
CATALYST

CH30 goes 0h MORE
SUBSTITUTED C

CH 3CH2OH 1 CHzCHOH

cat H 2SO 4