Alkene

1
Chapter 7

• Alkene
• Synthesis Reactions

2
sp2 ? sp3
p 172, Table 5.3
Diss. energy of double bond (H2CCH2) 611 kJ/mol
Diss. energy of sigma bond (CH3 CH3) 376 kJ/mol
Dissociation energy of pi bond 235 kJ/mol
Therefore, pi bond is more reactive than sigma
bond.
3
General Properties
No rotation about the pi bond.
Relatively nonpolar. Not soluble in water, but
soluble in hexane, ether, etc.
p 172, Table 5.3
1. Radical reactions take place at the allylic
position. 2. Allylic hydrogen is more acidic than
alkyl and vinylic hydrogen.
4
Alkene Synthesis
5
Synthesis
From halides - dehydrohalogenation (minus HX)
Elimination
From alcohol - dehydration (minus H2O)
6
Elimination Reaction
7
Answer Key
8
Alkene Reactions
9
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
10
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
11
Alkene HX
X Cl, Br, or I.
Carbocation intermediate - is planar,
incoming group can attack from above or below the
plane.
Markovnikov rule - regiochemistry.
Review Chapter 6.
12
Alkene HX
Electrophilic Addition.
13
Answer Key
14
Alkene HX - suppliment
Secondary halide - carbocation.
Primary halide - free radical.
?
?
15
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
16
Alkene X2
X Cl or Br. F is too reactive, I does not react.
Chloronium or bromonium ion intermediate.
Anti stereochemistry.
17
Alkene X2
18
Answer Key
trans-1,2,Dichloro-1,2-dimethylcyclohexane
1,2,Dibromopropane
19
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
20
Halohydrin
Alkene ? halohydrin.
Form bromonium ion intermediate. Then attack by
nucleophile.
Aromatic ring is inert.
Anti stereochemistry.
Markovnikov rule applies.
21
Halohydrin
22
Answer Key
1-bromo-2-propanol
trans-2-bromocyclopentanol or cyclopentene
bromohydrin
(E)-2-Chloro-1-methly-1-cyclopentanol
23
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
24
Oxymercuration
Alkene ? alcohol.
Intermediate is mercurinium ion (similar
to bromonium ion).
Anti stereochemistry.
Markovnikov rule applies.
25
Oxymercuration
26
Answer Key
27
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
28
Hydroboration
Alkene ? alcohol.
Intermediate is organoborane.
Syn stereochemistry.
Non - Markovnikov rule applies.
29
Hydroboration Mechanism
30
Hydroboration
31
Answer Key
32
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
33
Hydrogenation

• Reduction - formation of CH bond.
• PtO2 solid catalyst - heterogeneous reaction.
• syn chemistry.
• Alkenes are much more reactive than most other
  functional groups toward catalytic
  hydrogenation. - p251

34
Hydrogenation
35
Answer Key
36
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
37
Hydroxylation

• Forming 1,2-dialcohol or diol (glycol).
• Forming cyclic osmate intermediate therefore syn
  stereochemistry.

38
Hydroxylation
39
Answer Key
40
Breaking up 1,2-diol
41
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
42
Alkene Carbene
43
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
44
Simmons-Smith Reaction
45
Alkene Carbene
p 248 stereospecific Starting from a cis
alkene only cis disubstituted cyclopropane is
produced starting from a trans alkene, only
trans-disubstituted cyclopropane is produced.
46
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
47
Oxidation

• Reducing the length of the carbon skeleton.
• Alkene ? aldehyde and/or ketone.
• Oxidizing agents are ozone or potassium
  permanganate.

48
Alkene Ozone
49
Answer Key
50
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
51
Oxidation
Alkene Ozone
Alkene KMnO4
52
Alkene KMnO4
53
Answer Key
54
Additional KMnO4 Reaction
55
M
halogenation
anti
halohydrination
oxidation
M
anti
oxymercuration
M
oxidation
Alkene
hydroboration
non-M
syn
Simmons-Smith
syn
hydrogenation
syn
carbenation
syn
syn
hydroxylation
56
Polymerization

• Monomer ?? Polymer
• Process - initiation, propagation, and
  termination.
• Monomer unit repeating unit.

57
Polymerization
monomer
polymer
Monomer unit
Monomer unit
58
Polymerization Mechanism
Propagation
59
Alkene

• Sample Problems

60
What reagents would you use to synthesize each of
the following compounds starting with
(a)
(b)
(c)
(d)
(f)
(g)
(e)
61
Answer Key

• (a) HgAc2, THF/H2O, NaBH4
• (b) HBr, ROOR
• (c) OsO4, NaHSO3, H2O
• (d) KMnO4, H3O
• (e) BH3, THF, H2O2, OH-
• (f) CH2I2, Zn, ether
• (g) HgAc2, THF/CH3OH, NaBH4

62
Show the structures when
react with the following
reagents.

• 1) Borane in tetrahydrofuran, followed by basic
  hydrogen peroxide.
• 2) Ozone followed by zinc in acid medium.
• 3) Hot, concentrated potassium permanganate.
• 4) Hydrogen and platinum catalyst.
• 5) Hydrogen bromide in methylene chloride.
• 6) Bromine water.
• 7) Chlorine gas.
• 8) Methylene iodide pretreated with the
  zinc-copper alloy.
• 9) Mercuric acetate in methanol, followed by
  sodium borohydride.

63
Answer Key
5)
1)
6)
2)
7)
3)
8)
4)
9)
64
Page 270, problem 7.44
Compound A has the formula C8H8. It reacts
rapidly with KMnO4 to give CO2 and a carboxylic
acid, B (C7H6O2), but reacts with only 1 molar
equivalent of H2 on catalytic hydrogenation over
a palladium catalyst. On hydrogenation under
conditions that reduce aromatic rings, 4
equivalents of H2 are taken up, and hydrocarbon C
(C8H16) is produced. What are the structures of
A, B, and C? Write the reactions.
65
Answer Key
66
In contact with a platinum catalyst, an unknown
alkene reacts with three moles of hydrogen gas
to give 1-isopropyl- 4-methylcyclohexane. When
the unknown alkene is, ozonized and reduced, the
products are the following
67
Answer Key
All three steps use O3 and Zn, H,