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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
> >
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