Chapter 8
8.1 Name the following compounds:
(a)
CH3
CH3
CH3CHC
CCHCH3
2,5-dimethyl-3-hexyne
(b)
CH3
HC
CCCH3
CH3
3,3-dimethyl-1-butyne
(c)
H3CHC
CHCH
CHC
CCH3
2,4-octadiene-6-yne
(d)
H 3C
H3CH2CCC
CCH2CH2CH3
H 3C
3,3-dimethyl-4-octyne
(e)
H3C
H3CH2CCC
CH3
CCHCH3
H3C
2,5,5-trimethyl-3-heptyne
(f)
6-isopropyl-cyclodecyne
8.2 There are seven isomeric alkynes with the formula C6H10. Draw and name them.
Solution:
1-Hexyne
2-Hexyne
3-Hexyne
3-methyl-1-pentyne
4-methyl-1-pentyne
4-methyl-2-pentyne
3,3-dimethyl-1-butyne
8.3 What products would you expect from the following reactions?
(a)
H2
C
H3 C
C
C
H2
CH
+
Cl
H2
C
H 3C
2Cl 2
C
H2
Cl
C
CH
Cl
Cl
(b)
C
+
CH
C
HBr
CH2
Br
(c)
H2
C
H2
C
H 3C
C
H2
C
C
CH3
+
C 4H 9
HBr
8.4 What product would you obtain by hydration of the following alkynes?
C
Br
H
C
CH3
(a)
hydration
C 3H 7
C
C3H 7
C
C3H 7
H2
C
C
C3H 7
O
(b)
3HC
H3 C
CH
hydration
H2
C
C
C
3HC
C 3H 7
H3 C
CH
H2
C
C
O
8.5 What alkynes would you start with to prepare the following ketones?
O
O
(a)
CH3CH2CH2CCH3
(b)
CH3CH2CCH2CH3
Solution:
(a)
CH3CH2CH2C
CH (b)
CH3CH2C
CCH3
8.6 What alkyne would you start to prepare each of the following compounds by a hydroboration /
oxidation reaction?
O
CH3
CH2 CH
O
CH3CHCH2CCHCH3
(a)
CH3
(b)
Solution:
CH
CH3
C
CH3CHC
(a)
(b)
CCHCH3
CH3
8.7 How would you prepare the following carbonyl compounds starting from an alkyne?
C C 3H 7
H2
Br
O
O
solution:
Br
Br
HgSO4, H3O
O
O
1.BH3
2.H2O2 / NaOH
8.8 Using any alkyne needed, how would you prepare the following alkenes?
(a) trans-2-Octene
(b) cis-3-Heptene
(c) 3-Methyl-1-pentene
solution:
(a)
Li,NH3
(b)
H2
Lindlar catalyst
(c)
H2
Lindlar catalyst
8.9 Propose structures for alkynes that give the following products on oxidative cleavage by KMnO4:
(a)
CO2H
+
CO2
(b)
2CH3(CH2)7CO2H + HO2C(CH2)7CO2H
Solution: The structure is:
(a)
(b)
CH3(CH2)7C≡C(CH2)7C≡C(CH2)7CH3
8.10
The pKa of acetone, CH3COCH3, is 19.3. Which of the following bases is strong enough to deprotonate acetone?
(b) Na+ -C≡CH (pKa of C2H2 = 25)
(a) KOH (pKa of H2O = 15.7)
(c) NaHCO3 (pKa of H2CO3 = 6.4)
(d) NaOCH3 (pKa of CH3OH = 15.6)
Solution: (b)
Because pKa (C2H2) > pKa (CH3COCH3)
8.11 Show the terminal alkyne and alkyl halide from which the following products can be obtained. If
two routes look feasible, list both.
Answer:
(a)
H3CH2 CH2CC
H3CH2CH2C
C
C
CH3
3HCC
CH
CH
Br
CH3
Br
CH2CH2CH3
(b)
H3C
H3C
H3CHC
C
C
CH2CH3
H3CHC
CCH3
C
C
CH
Br
CH2CH3
CH
C
BrCH3
(c)
8.12 How would you prepare cis-2-butene starting from propyne, an alkyl halide, and any other
reagents needed? This problem can’t be worked in a single step. You’ll have to carry out more than one
reaction.
Answer:
H3CC
CH
NaNH2
NH3
BrCH3
THF
HC
H2
H3CC
CCH3
Lindar catalyst
H3CC
CCH3
CH
H3C
CH3
8.13 Beginning with 4-octyne as your only source of carbon and using any inorganic reagents necessary,
how would you synthesize the following compounds?
(a) Butanoic acid
(b) cis-4-Octene
(d) 4-Octanol (4-hydroxyoctane)
(c) 4-Bromooctane
(e) 4,5-Dichlorooctane
Solution: (a)
O
KMnO4
H3O
2
OH
(b)
H2
Lindler catalyst
(c)
H2
Lindler catalyst
HBr, ether
Br
(d)
H2
Lindler catalyst
1.BF3 , THF
2.H2 O2 , OHOH
(e)
H2
Lindler catalyst
X2
CH2Cl2
Cl
Cl
8.14 Beginning with acetylene and any alkyl halides needed, how would you synthesize the following
compounds?
(a) Decane
(b) 2,2-Dimethylhexane
(c) Hexanal
(d) 2-Heptanone
Solution: (a)
NaNH2
Na C
CH
CH3 CH2 CH2CH2CH2CH2CH2CH2Br
2H2
Pd/C
(b)
NaNH2
Na C
(CH3)3CCH2CH2Br
CH
2H2
Pd/C
(c)
NaNH2
Na C
CH
CH3CH2CH2CH2Br
1.BH3
2.H2O2
O
(d)
NaNH2
Na C
CH
CH3CH2CH2CH2CH2Br
H2 SO4, H2O
HgSO4
O
8.15 Name the following alkynes, and predict the products of their reaction with (i) H2 in the presence
of a Lindlar catalyst and (ii) H3O+ in the presence of HgSO4:
(a)
HC
(b)
CH3
H3C
H3C
C
C
C
H2
H2C
CH3
CH3
HC
C
H2
C
C
CH2
CH
H3C
Solution:
CH3
t
Ca
/L
in
dl
ar
2
H
SO
Hg
/H
4
+
O
3
O
H
i
/L
rC
la
nd
at
2
H
O
gS
/H
4
+
O
3
O
8.16 From what alkyne might each of the following substances have been made?
(b)
(a)
CH3
H2
C
CH
H3C
C
H2
H2
C
O
C
H
H2 C
H2 C
C H
CH3
H
C
Cl
C
C
H2
CH3
Cl
Solution:
(a) is from
CH3
H2
C
CH
H3C
H2C
C
CH
4-Methyl-pentyne
H2 C
H2 C
C H
CH3
H
C
C
CH
C
H2
and (b) is from 1-Ethynyl-2-methyl-cyclohexane
8.17 How would you prepare the following substances, starting from any compounds having four
carbons or fewer?
HO
HC
CH
(a)
H3 C
C
H2
CH2
C
H2
OH
HO
H
C
CH
Solution:
H3C
CH2
Zn(Cu)
Ether
H 3C
C
H2
CH2
HC
CH
C
H2
C
H2
O
H2
C
H2C
C
C
C
H2
(b)
CH3
H
O
H2
C
H2C
C
C
C
H2
CH
HgSO4
H
Solution:
H2
C
H2SO4, H2O
H2C
C
C
C
H2
CH3
H
8.18 The following cycloalkyne is too unstable to exist. Explain.
H2C
CH2
C
H2
Solution: It’s not possible to form a small ring containing a triple bond because the angle strain that
would result from bending the bonds of an SP-hybridized carbon to form a small ring is too great.
8.19 Give IUPAC names for the following compounds.
CH3
CH3 CH2C
CCCH3
CH3
a.
b.
CH3C
CCH2C
CH3
c. CH3CH
CC
CCH2CH3
CH3
CCHCH3
CH3
HC
CCCH2C
CH
CH3
d.
e. H2 C
CHCH
CHC
CH
CH2CH3
CH3CH2 CHC
f.
CCHCHCH3
CH2CH3
CH3
Solution:
a. 2,2-Dimethyl-3-hexyne
b. 2,5-Octadiyne
c. 3,6-Dimethyl-2-heptene-4-yne
d. 3,3-Dimethyl-1,5-hexadiyne
e. 1,3-Hexadiene-5-yne
f. 3,6-Diethyl-2-methyl-4-octyne
8.20 Draw structures corresponding to the following names:
a. 3,3-Dimethyl-4-octyne
b. 3-Ethyl-5-methyl-1,6,8-decatriyne
c. 2,2,5,5-Tetramethyl-3-hexyne
d. 3,4-Dimethylcyclodecyne
e. 3,5-Heptadien-1-yne
f. 3-Chloro-4,4-dimethyl-1-nonen-6-yne
g. 3-sec-Butyl-1-heptyne
h. 5-tert-Butyl-2-methyl-3-octyne
Solution:
a.
3,3-Dimethyl-4-octyne
b.
3-Ethyl-5-methyl-1,6,8-decatriyne
c. 3,6-Dimethyl-2-heptene-4-yne
d. 3,4-Dimethylcyclodecyne
e.
3,5-Heptadien-1-yne
Cl
f.
g.
3-Chloro-4,4-dimethyl-1-nonen-6-yne
3-sec-Butyl-1-heptyne
h. 5-tert-Butyl-2-methyl-3-octyne
8.21 The following two hydrocarbons have been isolated from various plants in the sunflower family.
Name them according to IUPAC rules.
(a)
H3C
C
H
C
H
C
C
C
C
C
H
C
H
C
H
C
H
C
H
CH2
C
C
C
C
C
C
C
C
C
C
C
H
CH2
(b)
H3C
SOLUTION:
(a)
(3E, 5E, 11E)-1,3,5,11-Tridecatetraen-7, 9-diyne.
(b)
1-Tridecene-3, 5, 7, 9, 11-pentayne
8.22. Predict the products of the following reactions.
H
H2, Pd/C
H2/Lindlar
SOLUTION:
A:
H2
C
H2
C
C
H2
B:
CH3
A
B
H
C
H
C
C
H
CH2
8.23 A hydrocarbon of unknown structure has the formula C8H10. On catalytic hydrogenation over the
Lindlar catalyst, 1 equivalent of H2 is absorbed. On hydrogenation over a palladium catalyst, 3
equivalents of H2 are absorbed.
a) How many degrees of unsaturation are present in the unknown?
b) How many triple bonds are present?
c) How many double bonds are present?
d) How many rings are present?
e) Draw a structure that fits the data.
Solution:
a)
4 degrees of unsaturation are present.
b) 1 triple bond is present.
c)
1 double bond is present.
d) 1 ring is present.
e)
The possible structure can be:
etc...
8.24 Predict the products from reaction of 1-hexyne with the following reagents:
a) 1 equiv HBr
b) 1 equiv Cl2
c) H2, Lindlare catalyst
d) NaNH2, in NH3, the CH3Br
e) H2O, H2SO4, HgSO4
f)2 equiv HCl
Solution:
HCl
a)
1-hexyne
Cl
Cl
Cl2
b)
1-hexyne
Cl
H
H
H
H2
Lindlar Catalyst
c)
1-hexyne
NaNH2
d)
1-hexyne
NH3
CNa
CH3Br
O
H2SO4,H2O
HgSO4
1-hexyne
e)
Cl
2HCl
1-hexyne
f)
Cl
8.25 Predict the products from reaction of 5-decyne with the following reagents:
(a) H2, Lindlar catalyst. (b) Li in NH3. (c) 1 equiv Br2. (d) BH3 in THF, then H2O2, OH-. (e) H2O,
H2SO4, HgSO4. (f) Excess H2, Pd/C catalyst.
Solution:
H
(a)
H
C4H9
C4H9
H
C4H9.
O
(b)
C4H9
C4H9.
(f)
C4H9
C4H9
H
Br
. (c)
O
C4H9
C4H9
. (d)
Br
C4H9
C4H9.
C4H9
(e)
8.26 Predict the products from reaction of 2-hexyne with following reagents:
(a) 2 equiv Br2. (b) 1 equiv HBr. (c) Excess HBr. (d) Li in NH3. (e) H2O, H2SO4, HgSO4
Solution:
Br
Br
H3C
H3C
(a)
Br
Br
H
Br
H3C
(d)
H
. (b)
H
H
etc.. .
H
H3C
H3C
(e)
Br
C3H7
C3H7
and
Br
C3H7.
Br
Br
C3H7
H
C3H7
+
C3H7
H3C
(c)
H3C
H
Br
H
O
C3H7
H3C
and
O
C3H7
8.27 Predict the products of the following reactions:
(a)
CH3CH2CH2CH2 CH2C CH
1.BH3,THF
2.H2O2
O
CH3CH2CH2 CH2CH2CH2 CH
Br
CH2
(b)
C
NaNH2,NH3
CH
Br
Br
CH3
C
NaNH2,NH3
CH
(c)
8.28 Hydrocarbon A has the formula C9H12 and absorbs 3 equivalents of to yield B,C9H18 ,when
hydrogenated over a Pd/C catalyst. On treatment of A with aqueous H2SO4 in the presence of
mercury(II), two isomeric ketones, C and D, are produced. Oxidation of A with KMnO4 gives a
mixture of acetic acid (CH3CO2H) and the tricarboxylic acid E. Propose structure for compounds
A-D, and write the reactions.
Solution:
A
H2
C C C CH3
C
H2 H2 O
C C C
E
(1)
CH3
B
H2 H2 H2
C C C CH3
D
H2 O H2
C C C CH3
H
HOOCH2C C CH2COOH
CH2COOH
H2
C C C CH3
(2)
H2
C C C CH3
(3)
H2
C C C CH3
H2 H2 H2
C C C CH3
H2
Pd/C
H2 H2 O
C C C
mercury(II)
H2SO4
KMnO4
CH3
H
HOOCH2C C CH2COOH
CH2COOH
8.29 How would you carry out the following reactions?
H2 O H2
C C C CH3
+
+
CH3COOH
O
(a)
(b)
H3CH2CC
CH
H3CH2 CC
CH
C
(c)
H2SO4, H2O
H3CH2C
HgSO4
1, BH3
CCH3
CH3CH2CH2CHO
2, H2O2
CH
C
C
CH3
NaNH2
CH3Br
H
C
(d)
CCH3
H
H2
Lindlar catalyst
(e)
H3CH2CC
(f)
CH
CH3CH2 CH2 CH2CH
KMnO4
CH2
CH3
CH3CH2CO2H
1. Br2
2. KOH, ethanol
CH3 CH2 CH2CH2C
CH
8.30 Occasionally, chemists need to invert the stereochemistry of an alkene, that is, to convert a cis
alkene to trans alkene, or vice versa. There is no one-step method for doing an alkene inversion, but
the transformation can be carried out by combining several reactions in the proper sequence. How
would you carry out the following reactions?
(a)
trans-5-Decene
(b)
cis-5-Decene
1. Br2
2. KOH, ethanol
3. H2 , Lindlar catalyst
1. Br2
cis-5-Decene
trans-5-Decene
2. KOH, ethanol
3. Li, NH3
8.31 Propose structures for hydrocarbons that give the following products on oxidative
cleavage by KmnO4 or O3
(a) CO2 + CH3(CH2)5CO2H
CO 2H
CH3CO 2H
(b)
+
(c) HO2(CH2)8CO2H
(d) CH3CHO + CH3COCH2CH2CO2H + CO2
(e) OHCCH2CH2CH2CH2COCO2H + CO2
Solution:
(a)
(b)
(c)
(d)
(e)
8.32 Each of the following syntheses requires more than one step. How would you carry them out?
(a)
CH3CH2 CH2C
CH3 CH2CH2CHO
CH
(B)
H
(CH3)2CHCH2C
CH2CH3
CH
(H3C)2 HCH2C
H
Solution: (a)
H2
Lindlar catalyst
1. O3
2. Zn/H3 O
O
(b)
(CH3 )2CHCH2C
CH
(CH3)2 CHCH2C
NaNH2
(CH3)2CHCH2 C
H
Li
CCH2CH3
CH3CH2 Br
CNa
CH2CH3
NH3
(H3C) 2HCH2C
H
8.33 How would you carry out the following transformation? More than one step is needed.
H
H
C
H2C
H3C
H
H
CH3
C
H2
CH2
H
H2
+
C
CH3
H
H
C
H
H2C
H3C
H
CH3
C
H2
CH2
8.34 How could you carry out the follow conversion? More than one step is needed.
?
CHO
Solution:
OH
BH3
PCC
H2O2/OH-
CH2Cl2
8.35 How would you carry out the following transformation? More than one step is needed.
CHO
Br
Br
Br2
KOH
Ethenal
CH2Cl2
C
C
CH
C
KNH2
K
CH3Br
Li
NH3
8.36 Synthesize the following compounds using 1-butyne as the only source of carbon, along with any
inorganic reagents you need. More than one step may be needed.
(a) 1, 1, 2, 2-Tetrachlorobutane
Solution:
Cl
HC
C
CH2
CH3
Cl2
CH2Cl2
CH2CH3
C
Cl2
CH2Cl2
C
H
H
Cl
Cl
Cl
C
C
Cl
Cl
CH2
CH3
(b) 1, 1-Dichloro-2-ethylcyclopropane
Solution:
H
HC
C
H2
C
CH3
H2
Lindlar catalyst
C
H
(c) Butanal
Solution：
H
Cl
CHCl3
KOH
C
CH2CH3
Cl
C
H2C
CH
CH2
CH3
H
HC
C
CH2
H2
CH3
H
C
Lindlar catalyst
H
H
OH
H
C
C
H
H
CH2
1. BH3, THF
C
2. H2 O2, OHCH2CH3
CH3
8.37 How would you synthesize the following compounds from Acetylene and any alkyl halides with
four or fewer carbons? More than one step may be required.
(a) CH3CH2CH2C CH
(b) CH3CH2C CCH2CH3
(c) (CH3)2CHCH2CH CH2
(e) CH3CH2CH2CH2CH2CHO
HC CH
O
(d) CH3CH2CH2CCH2CH2CH2CH3
NaNH2
Solution: (a)
CH3CH2CH2Br
HC C Na
NH3
THF
CH3CH2CH2C CH
(b)
HC CH
NaNH2
NH3
HC C Na
CH3CH2Br
THF
CH3CH2 C CH
CH3CH2Br
NaNH2
CH3CH2C CCH2 CH3
CH3CH2C C Na
NH3
THF
(c)
HC CH
NaNH2
NH3
HC C Na
(CH3 )2CHCH2Br
(CH3)2CHCH2C CH
H2
(CH3)2CHCH2CH CH2
Lindlar catalyst
(d)
NaNH2
NaNH2
CH2CH2CH2Br
CH3CH2CH2Br
HC C Na
CH3CH2 CH2C C Na
CH3CH2CH2C CH
NH3
NH
3
THF
THF
O
H2 SO4,H2O
CH3CH2 CH2CCH2CH2CH2CH3
CH3CH2CH2 C CCH2CH2CH3
HgSO4
HC CH
(e)
HC CH
NaNH2
CH3CH2CH2CH2Br
1.BH3
HC C Na
CH3CH2 CH2CH2C CH
NH3
2.H2O 2
THF
CH3CH2CH2 CH2CH2CHO
8.38 How would you carry out the following reactions to introduce deuterium into organic molecules?
(a)
D
D
H3CH2CC
?
CCH2CH3
C
C
C2H5
C2H5
(b)
?
H3CH2CC
CCH2CH3
C2H5
D
C
C
C2 H5
D
(c)
?
H3CH2CH2CC
(d)
CH
H3CH2CH2CC
CD
C
CH
DC
?
CD2
Solution:
D
CH3CH2C
CH3CH2C
D
D2
CCH2CH3
Lindlar catalyst
C2H5
Li,ND3
CCH2CH3
C2H5
D
C2H5
C2H5
D
Na+NH2H3CH2CH2CC
H3CH2CH2CC
CH
Na+
C
D2O
H3CH2CH2CC
CD
NH3
CD
C
CH
C
+
Na NH2
C
C
-
D2O
CD2
CD
D2
Lindlar catalyst
NH3
8.39 How would you prepare cyclodecyne starting from acetylene and any alkyl halide needed?
Solution:
H
Na
H
Na
+ 2 NaNH2
+
NH3
I
I
THF
8.40 The sex attractant given off by the common housefly is an alkene named muscalure. Propose a
synthesis of muscalure starting from acetylene and any alkyl halides needed. What is the IUPAC name
for muscalure?
cis- H3C(H2C)7HC
CH(CH2)12CH3
Solution: The IUPAC name for muscalure is cis-9-tricosene.
NaNH2
H
C
C
H3C(H2C)7
H
H3 C(H2C)7
(CH2) 12CH3
C
H
C
C
H
Br
NaNH2
H3C(H2C)7
C
H2
Lindlar
H3C(H2C)12
H3C(H2C)7
C
Br
C
(CH2) 12CH3
H
8.41 Compound A (C9H12) absorbed 3 equivalents of H on catalytic reduction over a palladium catalyst
to give B (C9H18). On ozonolysis , compound A gave, among other things, a ketone that was identified
as cyclohexanone. On treatment with, gave C (C10H14) .Give the structure of A, B, C.
Solution:
A:
B:
C:
8.42 Hydrocarbon A has the formula C12H8. It absorbs 8 equivalents of H2 on catalytic reduction over
a palladium catalyst. On ozonolysis, only two products are formed: oxalic acid (HO2CCO2H) and
succinic acid (HO2CCH2CH2CO2H). Write the reactions, and propose a structure for A.
Slution:
8H2
Pd/C
cyclododecane
O3
2 HO
O
O
C
C
O
OH + 2 HO
C
8.43 Identify the reagents a-c in the following scheme:
a
b
c
H
`
H
Solution:
1. NaNH2, NH3
2. CH3CH2Br
H2 / Lindlar Cat
CH2I2 / Zn(Cu)
H
H
8.44 Organometallic reagents such as sodium acetylide undergo an addition reaction with ketones, give
OH
alcohols:
O
1. Na+ C
C
R
R
2. H3O
CH
+
C
R
C
R
CH
How might you use this reaction to prepare 2-methyl-1,3-butadiene, the starting material used in
the manufacture of synthetic rubber
Solution：
O
CH2CH2
C
O
1. Na+ C
OH
CH
H2 SO4, H2O
+
THF
2. H3 O
H2
Lindlar catalyst
8.45 Erythrogenic acid, C18H26O2, is an acetylenic fatty acid that turns a vivid red on exposure to
light. On catalytic hydrogenation over a palladium catalyst, 5 equivalents of H2 are absorbed, and
stearic acid, CH3(CH2)16CO2H, is produced. Ozonolysis of erythrogenic acid gives four products:
formaldehyde, CH2O; oxalic acid, HO2CCO2H; azelaic acid , HO2C (CH2)7CO2H; and the aldehyde
acid OHC(CH2)4CO2H. Draw two possible structures for erythrogenic acid, and suggest a way to tell
them apart by carrying out some simple reactions.
Solution
The problem can be described as following illustration:
O
H
C
H
O
C18H26O2
5H2
H3C
C18H36O2
H2
C
O3
Zn H3+O
C
OH
C
OH
O
16
C
OH
O
O
O
H2
C
HO
OH
7
O
HO
O
H2
C
OH
4
And first we can predict the unsaturated degree of starting material by the fact that it can absorb 5 H2
and form a carboxylic acid. So The molecular has 5 double bonds or 1 triple bond and 3 double bonds
or 2 triple bonds and 1 double bond besides a C=O bond, and there is no rings in the molecular.
Second we can think about the products after it is treated with
problem.
O3
,and we can get the solultion t the
H
O
HO
C
C
C
H2
C
C
7
C
H2
C
C
4
H
C
H
H
O
HO
C
H2
C
C
7
C
C
C
H2
C
C
4
H
CH
You can see two possible starting materials according to the problem exactly. However, we can tell
them apart from each other by following method.
STEP1
Treat the SM with Lindlar catalyst, and then we can get the product only contains double bond but
no triple bond.
STEP2
Treat the product get from the step with O3 ,H3O+ and Zn and then we can get the products
following.
STEP3
Analyze the products and you can find the differences written following between the different SMs .
At last we can tell them apart easily.
HCHO
H
O
HO
C
O
C
C
H
C
H
H2
C
C
7 H
C
H
H2
C
4
H
Zn H3O
C
O3
HC
O
H2
C
4
O
H
HC
HO
CH
O
H2
C
7
CH
O
O
C
CH
HCHO
O
H
O
HO
C
C
H2
C
C
7H
C
H
C
H
H2
C
C
H
4
H2
C
HC
H Zn H O
3
CH
O
O3
4
CH
O
C
H2
C
O
O
C
C
HO
HO
O
7
CH
OH
8.46 Terminal alkynes react with Br2 and water to yield bromo ketones. For example:
O
Br2 , H2O
CH2Br
Propose a mechanism for the reaction. To what reaction of alkenes is the process analogous?
Solution:
H
H
Br
O
H
H
Br
O
H
Br
Br
H
O
H
H
O
H
O
Br
rearrangement
Br
The mechanism here is just like the halohydrin of alkene.
8.47 A cumulene is a compound with three adjacent double bonds. Draw an orbital picture of
cumulene. What kind of hydridization do the two central carbon atoms have? What is the geometric
relationship of the substituents on one end to the substituents on the other end? What kind of isomerism
is possible?
R 2C
C
C
CR 2
Solution:
(a) They are sp hybridized.
R
C
C
C
R
C
R
R
(b) The geometric relationship of the substituents on one end to the substituents on the other end is cis
and trans.
(c) Stereoisomers.
8.48 Reaction of acetone with D3O+ yields hexadeuterioacetone. This is, all the hydrogens in acetone
are exchanged for deuterium. Review the mechanism of alkyne hydration, and then propose a
mechanism for this deuterium incorporation.
O
H3C
C
O
D3O+
C
CH3
D3C
Acetone
CD3
Hexadeuterioacetone
Solution:
O
O H
C
H3C
CH2
H
OH
C
C
H3C
……
H3C
CH2
D3O+
CH2
D
O
C
D3C
CD3