L
TOPIC 8. ADDITIONS TO ALKENES
AND ALKYNES (Chapter 8 and
parts of chapters 7, 10 and 11)
OBJECTIVES
1. Describe mechanisms for addition reactions of alkenes and alkynes
2. Predict the structure of the product(s) of addition reactions
3. Understand the mechanisms which explain the regiochemical and
stereochemical outcome of addition reactions
4. Use combination of substitution, elimination and addition chemistry to
propose synthetic routes to useful value-added compounds
D.M. Collard 2007
ADDITION REACTIONS
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
Addition of H2
- H2/Pd (alkene, alkyne)
- H2/Lindlar catalyst (alkyne → cis alkene)
- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal
- Markovnikov
- anti-Markovnikov
Addition of H2O
- H3O+ (regiochemistry)
- Oxymercuration-demercuration (regiochemistry, stereochemistry)
- Hydroboration-oxidation (regiochemistry, stereochemistry)
- hydration of alkynes (regiochemistry)
Addition of Hal2
- Hal2 (regiochemistry, stereochemistry)
- Hal2/H2O (regiochemistry)
Generation and reaction of carbenes
Epoxidation
Nucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)
syn-Hydroxylation
Oxidative cleavage of alkenes and alkynes
- KMnO4
- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
HYDROGENATION OF ALKENES
AND ALKYNES
Hydrogenation of Alkenes
CH3
CH3
D.M. Collard 2007
H2
Pd or Pt
S:7.12-7.14
Prob:
7.40-42;
8.30e,g,i,
37,45
Hydrogenation of Alkynes
Complete Hydrogenation
H2
C C
Pt or Pd
cis-Semihydrogenation
C C
H2
Pd/CaCO3
N
Dissolving Metal Reduction
C C
2Li, 2CH3OH
NH3 (solvent)
Li
C C
Li
Li
D.M. Collard 2007
PREVIEW OF REACTIVITY
S:8.1
Alkenes and Alkynes are Weakly _____ and Weakly
_____________
H
Br
C C
E
C C
E
ADDITION OF HYDROGEN HALIDES
TO ALKENES AND ALKYNES
Overview
C C
H C C Cl
C C
H Br
H C C Br
CH3
CH3
I
H
D.M. Collard 2007
S:8.28.3;18.19;
10.9
Prob:
8.27,28a,b,f
,j,29b-g,35
Addition of H-Hal to Alkenes
Mechanism
C C
H
Br
Regiochemistry
H3C
C CH2
H
Br
H3C
Markovnikov’s Rule
In the addition of HX to an unsymmetrical alkene, the hydrogen adds to the
_____________ substituted carbon and the X groups adds to the
_____________ substituted carbon.
D.M. Collard 2007
The Basis of Markovnikov’s Rule: Stability of Carbocations
H3C
C CH2
HBr
H3C
The more substituted carbocation is formed. Remember hyperconjugation!
H
C
C
H
H
Mechanistic Restatement of Markovnikov’s Rule
In the ionic addition of HX to an unsymmetrical alkene, protonation gives the
more stable carbocation as an intermediate.
Stereochemistry of H–Hal Addition to Alkenes
H Br
Br
H
C
D.M. Collard 2007
Br
Anti-Markovnikov Addition of H-Hal to Alkenes
H
C CH2
H
Br
H3C
Mechanistic Rationale for Anti-Markovnikov Addition
Addition of H-Hal to Alkynes
R C C H
R C C R'
D.M. Collard 2007
HCl
CCl4
~ MAKE
FLASHCARDS ~
Hydrogenation
Dissolving metal reduction
Hydrogenation over Lindlar catalyst
Markovnikov addition of H-Hal
Anti-Markovnikov addition of H-Hal
…..more next lecture
ADDITION REACTIONS
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
Addition of H2
- H2/Pd (alkene, alkyne)
- H2/Lindlar catalyst (alkyne → cis alkene)
- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal
- Markovnikov
- anti-Markovnikov
Addition of H2O
- H3O+ (regiochemistry)
- Oxymercuration-demercuration (regiochemistry, stereochemistry)
- Hydroboration-oxidation (regiochemistry, stereochemistry)
- hydration of alkynes (regiochemistry)
Addition of Hal2
- Hal2 (regiochemistry, stereochemistry)
- Hal2/H2O (regiochemistry)
Generation and reaction of carbenes
Epoxidation
Nucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)
syn-Hydroxylation
Oxidative cleavage of alkenes and alkynes
- KMnO4
- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
D.M. Collard 2007
L
SYNTHESIS OF ALCOHOLS
BY HYDRATION OF ALKENES
Addition of Water to Alkenes
H2O
C C
H2SO4
H OH2
Proceeds via Markovnikov addition
D.M. Collard 2007
S:8.4-8.11
Prob:
8.27c,32,58
11.33,35(ag),38(a,d),
39,46,48
Rearrangements During Acid Catalyzed
Hydration of Alkenes
OH
CH3
H2SO4
H
H 2O
CH3
H
not:
OH
CH3
Intermediate carbocations can rearrange.
Oxymercuration-Demercuration of Alkenes
e.g.,
1. (CH3CO2)2Hg
H2O
OH
2. NaBH 4, NaOH
Step 1: Oxymercuration
C C
(CH3CO2)2Hg
H2O
O
CH3
HO
Hg O
Step 2: Demercuration
O
CH3
HO
D.M. Collard 2007
Hg O
NaBH4
NaOH
HO
H
Mechanism
O
O
O
Hg
O
O
O
Hg
H2O
Hydroboration-Oxidation: Anti-Markovnikov
Hydration of Alkenes
e.g.,
CH3
H
1. B2H6
2. H2O2
NaOH
CH3
OH
Step 1: Hydroboration
B2H6
C C
H
BH2
Step 2: Oxidation
H
D.M. Collard 2007
BH2
H2O2
NaOH
H
OH
Mechanism: Regiochemistry
B2H6
B
BH3
H
H
B
H2O2
NaOH, H2O
Stereochemistry
CH3
CH3
H
B
D.M. Collard 2007
CH3
H
OH
Hydration of Alkynes (covered in 16.5B)
R C C H
H2O
Hg++, H2SO4
R
H
C
HO
C
H
SYNTHETIC STRATEGIES
Problem: Synthesize cis-1-cyano-2-methylcyclohexane (shown
below) using any hydrocarbon.
CN
D.M. Collard 2007
Prob:7.24
Problem: Female houseflies attract males with a pheromone which
has been shown to be Z-9-tricosene (C23H46). Synthesize this
compound starting with organic compounds containing 13 or less
carbon atoms.
n-C8H17
H
H
n-C13H27
ADDITION REACTIONS
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
Addition of H2
- H2/Pd (alkene, alkyne)
- H2/Lindlar catalyst (alkyne → cis alkene)
- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal
- Markovnikov
- anti-Markovnikov
Addition of H2O
- H3O+ (regiochemistry)
- Oxymercuration-demercuration (regiochemistry, stereochemistry)
- Hydroboration-oxidation (regiochemistry, stereochemistry)
- hydration of alkynes (regiochemistry)
Addition of Hal2
- Hal2 (regiochemistry, stereochemistry)
- Hal2/H2O (regiochemistry)
Generation and reaction of carbenes
Epoxidation
Nucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)
syn-Hydroxylation
Oxidative cleavage of alkenes and alkynes
- KMnO4
- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
D.M. Collard 2007
L
ADDITION OF BROMINE AND CHLORINE
TO ALKENES AND ALKYNES
Overview
Cl2
C C
CCl4
2 Cl2
C C
CCl4
Cl
Cl
Cl Cl
Cl
Cl
Br
Br2
Br
+
HCCl3
Br
50% S,S trans
Br
50% R,R trans
Addition of Hal2 to Alkenes
Stereochemistry
H
H3C
CH3
H
CH3
H3C
D.M. Collard 2007
H
H
Br2
Br
H
Br2
H
CH3
H3C
Br
Br
CH3
H
H 3C
H3 C
H
Br
H
H
H3 C
Br
Br
Br
H
CH3
Br
CH3
H
S:8.128.14;8.18
Prob:
8.30(c,d),
31,54
Mechanism
H
H3C
H
CH3
Br
Br
Formation of Halohydrins
Cl2
C C
H2O
CH3
Br2
H2O
D.M. Collard 2007
Cl
OH
OH
CH3
Br
Mechanism
H
H
Cl2
H
CH3
H2O
Cl
Cl
Addition of Hal2 to Alkynes
R C C H
R C C R'
D.M. Collard 2007
Br2
HCCl3
ADDITION REACTIONS
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
Addition of H2
- H2/Pd (alkene, alkyne)
- H2/Lindlar catalyst (alkyne → cis alkene)
- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal
- Markovnikov
- anti-Markovnikov
Addition of H2O
- H3O+ (regiochemistry)
- Oxymercuration-demercuration (regiochemistry, stereochemistry)
- Hydroboration-oxidation (regiochemistry, stereochemistry)
- hydration of alkynes (regiochemistry)
Addition of Hal2
- Hal2 (regiochemistry, stereochemistry)
- Hal2/H2O (regiochemistry)
Generation and reaction of carbenes
Epoxidation
Nucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)
syn-Hydroxylation
Oxidative cleavage of alkenes and alkynes
- KMnO4
- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
L29
ADDITION OF CARBENES TO ALKENES
What is a Carbene?
What is a Carbenoid?
H2C N N
Cl
Cl
C H
Cl
D.M. Collard 2007
K
OtBu
CH2
I CH2 I
I CH2 Zn I
S:8.15
Additions to Alkenes
CH2N2
C C
CH2
or
CH2I2, Zn
CCl2
H
CHCl3
KOtBu
CH3
H
Mechanism
H
H3C
H
CH3
CH2
S:11.1311.15
EPOXIDES
Synthesis
O
R
O
MMPP
O O H
RCO3H
(peroxyacid)
O
RCO3H
(peroxyacid)
O
OOH
O
O
O
Mg2
2
D.M. Collard 2007
Prob:
11.43,44
OOH
mCPBA
Cl
Nucleophilic Ring-opening
O
H 3 O+
or
HO-, H2O
HO
OH
OH
Stereochemistry
O
OH
Regiochemistry
O
RO
OH
RO
O
ROH, H+
OR
HO
D.M. Collard 2007
Addition of Other Nucleophiles
O
OH
C N
NC
H2 O
O
C C R
R
C
liquid NH3
excess
O
NH2R
CH3OH
OH
C
OH
RHN
S:8.168.17,8.20
OXIDATION OF ALKENES
AND ALKYNES
Prob:
8.27(k,n),30
(j,k),46,47
Syn-Hydroxylation of Alkenes
C C
1. OsO4
2. NaHSO3
or
KMnO4,
NaOH, H2O
cold
KMnO4,
NaOH, H2O
cold
HO
OH
OH
OH
D.M. Collard 2007
Oxidative Cleavage of Alkenes
Permanganate Oxidation
1. KMnO4
NaOH, H2O, Δ
2. H3O+
O
+
O
OH
OH
1. KMnO4
NaOH, H2O, Δ
2. H3O+
O
CO2
+
Ozonolysis
O
O
O
O
O
1. O3, –78 °C
2. Zn, CH3CO2H
H
O
H
D.M. Collard 2007
O
O
Oxidative Cleavage of Alkynes
1. O3
2. CH3CO2H
R C C R'
or
1. KMnO4, NaOH
2. H3O+
O
O
R
R'
OH
HO
Problem: Compound X (C10H18) gave pentanoic acid upon reaction with basic
potassium permanganate followed by acidification. What is the structure of
compound X?
ADDITION REACTIONS
Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5
Addition of H2
- H2/Pd (alkene, alkyne)
- H2/Lindlar catalyst (alkyne → cis alkene)
- dissolving metal reduction (alkyne → trans alkene)
Addition of H-Hal
- Markovnikov
- anti-Markovnikov
Addition of H2O
- H3O+ (regiochemistry)
- Oxymercuration-demercuration (regiochemistry, stereochemistry)
- Hydroboration-oxidation (regiochemistry, stereochemistry)
- hydration of alkynes (regiochemistry)
Addition of Hal2
- Hal2 (regiochemistry, stereochemistry)
- Hal2/H2O (regiochemistry)
Generation and reaction of carbenes
Epoxidation
Nucleopihilic ring opening reactions of epoxides (H2O, ROH, HCN, RMgHal)
syn-Hydroxylation
Oxidative cleavage of alkenes and alkynes
- KMnO4
- Ozonolysis
Radical Polymerization
~MAKE FLASHCARDS AFTER EACH LECTURE~
D.M. Collard 2007
L
RADICAL POLYMERIZATION OF
ALKENES (CHAIN-GROWTH POLYMERS)
H2C CH2
radical
E
initiator
(CH2CH2)n
E = end group
S:10.10
E
n~40,000
About 60 x 109 pounds of ethylene are manufactured and used each year,
primarily to make polyethylene
Roll of Radical Initiator (Chain Initiation)
O
R
O
O O
R
Chain-Growth (Chain Propagation)
R
H2C CH2
R CH2CH2 + (n+1) H2C CH2
R CH2CH2 (CH2CH2)n
CH2CH2
End of Growth (Chain Termination)
Polymer
CH2CH2
CH2CH2
combination
2 Polymer
CH2CH2
disproportionation
D.M. Collard 2007
Polymer
CH CH2
Polymer
CH2CH3
Polymer
Common Chain-Growth Polymers
Monomer
Polymer
Name(s)
(CH2 CH2)n
H2C CH2
polyethylene
CH3
polypropylene
(CH2 CH)n
Cl
Cl
poly(vinyl chloride), PVC
(CH2 CH)n
CN
CN
polyacrylonitrile, "Orlon"
(CH2 CH)n
CH3
poly(methyl methacrylate)
Lucite, Plexiglass
(CH2 C)n
CO2CH3
CO2CH3
S:8.21
SYNTHETIC STRATEGIES
Prob:
8.218.26,44
Add to your chart of organic reactions
Additions
b
su
Addn
Elimn
Substn
H
C C
OH
su
bs
tit
Elimn
C C
Substn
ns
Addn
Br
ut
io
H2/Pt
n
H
dd
n
C C
Zn, HBr
A
d
El d n
im
Br Br
A
H
ns
Add
n
Br, hν
C C
io
ut
Elim
n
H
it
st
H2/Pt
C C
Additions
No more reactions! For now!!!
D.M. Collard 2007
DESIGNING SYNTHESES
One Step Syntheses
This is just the opposite of learning reactions - just think backwards.
Although one step syntheses are relatively easy, they are harder than
learning reactions.
Two Step Syntheses
This is involves considerable imagination and is quite different than “just
the opposite of learning reactions”. You must be able to conceive of the
intermediate. However, there is a direct link between the intermediate and
both the product and the starting material. Think “retro” (retrosynthesis) how do you synthesize the product from anything? Can you then
synthesize your proposed synthetic intermediate from the starting
material?
Starting material(s)
step 1
reaction
intermediate
step 2
?
Product
?
Three Step Syntheses
Three design of three-step organic syntheses requires a little more imagination
and can be a little more difficult than two-step syntheses. You must be able to
conceive of two intermediates. In this case there may not be a clear link
between intermediate one and the product or intermediate two and the starting
material. Again “think retro”. Can you think of ANY compounds that could be
converted to the product by chemistry you know? Can you then think of one or
more compounds that could be converted to these proposed intermediates by
chemistry you know? Can any of these second proposed intermediates be
synthesized from the starting material?
Starting material(s)
step 1
reaction
intermediate 1
step 2
reaction
intermediate 2
step 3
Product
interm. C
interm. A
Product
interm. B
interm. D
interm. E
starting
interm. F
material(s)
interm. G
D.M. Collard 2007
Potential
Problem: Solomons 8.31(b). Show how 1-butyne could be synthesized
from each of the following: (b) 1-chlorobutane
Cl
Problem:
D.M. Collard 2007
Br
From any alkane
Problem:
Br
From
Problem:
From
HO
Br
D.M. Collard 2007
Br
Problem: Propose a synthesis of 1-methyl-1,2cyclopentanediol (with the two hydroxy groups trans to one
another) from methylcyclopentane.
CH3
CH3
OH
OH
Problem: An insect physiologist required 4Z-hexen-2-ol for the study of
insect pheromones. Propose a synthesis of 4Z-hexen-2-ol from propene.
OH
D.M. Collard 2007
Prob:
11.30,35,
37,38,46
TOPIC 8 ON EXAM 4
Types of Questions
- Describe addition reaction mechanisms
- Predict the products of addition reactions
The problems in the book are good examples of the types of problems
on the exam.
Preparing for Exam 4:
- Work as many problems as possible.
- Work in groups.
- Do the “Learning Group Problem” at the end of the chapter.
- Work through the practice exam
D.M. Collard 2007