alkenes, alkynes pt 2(2)

Which is the correct structure for E-3-bromo-2-chloro-2-pentene?

C C

CH3

Cl

CH2CH3

Br

C C

CH3

Cl

Br

CH2CH3

C C

CH3

Br

Cl

CH2CH3

C C

CH3

Br

CH2CH3

Cl

1. 2.

3. 4.

Alkenes: StabilityThe stability of alkenes depends upon number of substituents

Stability of Disubstituted Alkenes

H3C

H3C H

H H3C

H H

CH3 H

H3C H

CH3

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REACTION OF ALKENESELECTROPHILIC ADDITION & OXIDATION

Reactive Sites of Alkenes & Alkynes

CH3

H3C

H3C C CH

Alkenes: Electrophilic Addition

Electrophilic addition to the double bond is a two-step process

R

R

R

R

+ Y+ + Z-

RR

Y

Z

RR

electrophile

nucleophile

Alkenes: Electrophilic Addition

Alkenes: Electrophilic Addition

Alkenes: AE - Hydrogenation CH3

+ H2

Pt/CCH3

H

H

With the help of metal catalysts, H2 adds to the double bond.

(Catalytic Reduction)

Alkenes: AE - Hydrogenation

Alkenes: AE - Hydrogenation

Alkenes: AE - Halogenation

Alkenes: AE - Halogenation

Alkenes: AE - Hydrohalogenation

Electrophilic reagents we can use are hydrogen halides:HF, HCl, HBr, HI

Alkenes: AE - Hydrohalogenation

Alkenes: AE - Hydration

H3CCH2

CHCH2

+ H2OHCl, trace

OH

H3CCH2

CHCH2

H

1-butene 2-butanol

Alkenes: AE - Hydration

AE – Markovnikov’s Rule

We obtain both products; however, one is the

major product.

HII

H I

H

1-methylcycohexene 1-iodo-1-methyl-cyclohexane

2-iodo-1-methyl-cyclohexane

Major product Minor product

+

We have a regioselective reaction.

AE – Markovnikov’s Rule

• In the addition of HX or H2O to an alkene, H adds to the C of the double bond having the greater number of hydrogens.

AE – Markovnikov’s Rule

AE – Markovnikov’s Rule

Carbocation Stability

Carbocation Stability

AE – Markovnikov’s Rule

AE – Markovnikov’s Rule

HBr

Br

H

+H

Br1-bromo-1-methyl-cyclopentane

1-bromomethyl-cyclopentane

A B

AE – Markovnikov’s Rule

Alkenes: AE – Addition of Alcohols Alcohols react the same way as water

C CH2

H3C

H3C+ CH3CH2OH

H+ H3CCH3

CH3

O

H2C CH32-methylpropene ethanol

tert-butyl-ethyl ether

Note: the reaction works only in the presence of acid.

Alkenes: AE – Addition of Alcohols