Chapter 8 Alkenes and
Alkynes II: Addition
Reactions
ORGANIC CHEMISTRY
Chapter 8
8.1 Introduction: Additions to Alkenes
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
C
C
Chapter 8
+ A B
A C
C B
Electrophilic addition
H X
H OSO3H
C
C
H OH
HA
X X
H C
C X
H C
C OSO3H
H C
C OH
X C
C X
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
Electrophiles Are Lewis Acids
A B
+
Electrophile
A
C
C
C
Nucleophile
A
C
C
+ B
Carbocation
C
B
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
8.2 Addition of Hydrogen Halides to
Alkenes: Markovnikov’s Rule
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
C
C
Chapter 8
H C
+ H X
Reactivity:
C X
HI >HBr > HCl >HF
(CH3)2C CH2 > CH3CH CHCH3 >
~
~ CH3CH CH2 > CH2 CH2
CH3CH2CH
CH2 + HBr
HOAc
CH3CH2 CH CH3
Br
(CH3)2C
CH2 + HCl
HOAc
CH3
CH3 C
Cl
80%
CH3
100%
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
Markovnikov’s rule
In the addition of HX to an unsymmetrically
substituted alkene, the hydrogen atom adds to the
carbon atom of the double bond that already has
the greater number of hydrogen atoms and that
the X group adds to the carbon having more alkyl
substituents.
Markovnikov’s rule can be restated by saying
that, in the addition of HX to an alkene, the more
stable carbocation intermediate is formed.
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
Mechanism
Step 1
Step 2
C
C
H C
(CH 3)2C
+ H X
C
+ X
slow
fast
CH2 > CH 3CH
H C
H C
C
C X
CHCH 3
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
8.2A Theoretical Explanation of
Markovnikov’s Rule
CH3CH
CH2
H Br
CH3CH2CH2
1° Carbocation
(less stable)
CH3CHCH3
2° Carbocation
(more stable)
Br
Br
CH3CH2CH2Br
1-Bromopropane
(little formed)
CH3CHCH3
Br
2-Bromopropane
(main product)
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
8.2B Modern Statement of
Markovnikov’s Rule
In the ionic addition of an unsymmetrical
reagent to a double bond, the positive portion of
the adding reagent attaches itself to a carbon
atom of the double bond so as to yield the more
stable carbocation as an intermediate.
H3C
H3C
δ
C CH2 +
I
δ
Cl
H3C
C CH2
H3C
I
Cl
CH3
H3C C CH2
Cl I
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
8.2C Regioselective Reaction
(区域选择性反应)
When a reaction that can potentially two or
more constitutional isomers actually produces
only one ( or a predominance of one), the
reaction is said to be regioselective.
CH3CH CH2
H Br
CH3CHCH3
Br
2-Bromopropane
(main product)
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
8.2D An Exception to Markovnikov’s Rule
When alkenes are treated with HBr in the presence of
peroxides the addition occurs in an anti-Markovnikov
manner in the sense that the hydrogen atom becomes
attached to the carbon atom with the fewer hydrogen
atoms.
CH3CH
F 3 CCH
CH2 + H Br
ROOR
(peroxide)
CH 2 ＋ HCl
CH3CH2CH2Br
F 3 CCH 2 CH2 Cl
Electron-withdrawing group: CN, COOH, NO2 et al.
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
Mechanism
O
O
O
Ph C O
O
O C Ph
Ph C O
Ph C O
+ HBr
O
Ph C OH + Br
CH3CH CH2 + Br
CH3CH CH2Br
CH3CH CH2Br + HBr
CH3CHCH2Br + Br
H
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
8.3 Stereochemistry of the Ionic
Addition to an Alkene
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
CH3CH2CH
Chapter 8
CH2 + H Br
*
CH3CH2CH
CH2H
Br
C H 3 CH 2 C H
CH2 + H
Br
CH 3 C H 2
C
H
CH3
Br
CH 3 CH 2 C
CH 3 CH 2
C
H
+ Br
CH 3
CH 3 CH 2
C
H
CH 3
H
CH 3
Br
+ HBr
H 3C
CH 3
HH 3 C
CH 3H
CH 3Br
Br CH 3
Notes:环烯烃与HX加成,一般得到以反式加成为主的产物.
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
8.4 Addition of Sulfuric Acid to
Alkenes
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
C
C
C
H
Chapter 8
+ H OSO3H
C
H
C
OSO3H
OSO3H
C
Alkyl hydrogen sulfate
Notes: 1.H2SO4 is cold and concentrated sulfuric acid.
2. Markovnikov’s Rule addition.
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
8.4A Alcohols from Alkyl Hydrogen Sulfates
CH2 CH2 + H2SO4(98%)
CH3CH CH2 + H2SO4(80%)
(CH3)2C CH2 + H2SO4(50%)
CH3CH2OSO3H
H2O
(CH3)2CHOSO3H
(CH3)3COSO3H
H2O
CH3CH2OH + H2SO4
H2O
(CH3)2CHOH + H2SO4
(CH3)3COH + H2SO4
Notes: Indirect hydration to prepare alcohols.
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 8
Addition of carboxylic acids, alcohols,
and phenols to alkenes
C H2
CH 2
C H 2 + C H 3 C O 2H
( C H 3 )2 C
CH 2
C H 3 (C H 2 ) 5 C H
H+
C H 3C H 2O 2C C F3
C H 2 + C F3C O 2H
H
C H 3C H 2O 2C C H 3
H B F4
+ C H 3O H
10 0 ℃
CH2 + HO
( C H 3) 3 C O C H 3
C (C H 3 ) 3
C (C H 3 ) 3
C H 3 (C H 2 ) 5 C H O
CH3
67%
Notes:Markovnikov’s Rule addition.
Department of Chemistry, Xiamen University