Chapter 8—Alkenes: Reactions and Synthesis
SHORT ANSWER
Exhibit 8-1
To answer the question(s) below consider the following reaction:
When cyclohexene reacts with chlorine in carbon tetrachloride the trans-dihalide is formed.
1.
Refer to Exhibit 8-1. Write the complete stepwise mechanism for this reaction. Be sure to
show all intermediate structures and all electron flow using arrows.
ANS:
2.
a.
b.
c.
d.
Refer to Exhibit 8-1. Since the two chlorine atoms add to opposite faces of the cyclohexene
double bond, we say that the reaction occurs with:
syn stereochemistry
cis stereochemistry
anti stereochemistry
retention of stereochemistry
ANS:
c
3.
a.
b.
c.
d.
Refer to Exhibit 8-1. The observed stereochemistry of addition of chlorine to cyclohexene is
explained by the intermediacy of a:
cyclonium ion
carbocation
carbene
chloronium ion
ANS:
d
1
Alkenes: Reactions and Synthesis
4.
Refer to Exhibit 8-1. Provide the IUPAC name for the product of the reaction of
cyclohexene with chlorine.
ANS:
trans-1,2-dichlorocyclohexane
5.
Draw both chair conformations of trans-1,2-dichlorocyclohexane on the templates provided
below. Circle the least stable conformation.
ANS:
Exhibit 8-2
Consider the reaction sequence below to answer the following question(s):
2
Chapter 8
6.
Refer to Exhibit 8-2. Write the complete reaction mechanism for the first step of this
reaction sequence. Show all electron flow with arrows and show all intermediate structures.
ANS:
7.
a.
b.
c.
d.
Refer to Exhibit 8-2. The intermediate in the first step of this reaction sequence is called a:
carbocation
cyclonium ion
mercurinium ion
mercapto species.
ANS:
c
8.
a.
b.
c.
d.
Refer to Exhibit 8-2. In the second step of this reaction sequence, the organomercury
compound is treated with sodium borohydride, NaBH4, to yield the alcohol product. This
replacement of a carbon-mercury bond with a carbon-hydrogen bond is termed:
an oxidation
a reduction
a hydroxylation
a cycloaddition
ANS:
b
3
Alkenes: Reactions and Synthesis
Exhibit 8-3
Consider the reaction below to answer the following question(s).
Alkenes may be hydrated by the hydroboration/oxidation procedure shown.
9.
Refer to Exhibit 8-3. The intermediate formed in the first step of this reaction is:
b.
a.
d.
c.
ANS:
b
10.
a.
b.
c.
d.
Refer to Exhibit 8-3. Hydroboration of alkenes is an example of:
a rearrangement reaction.
a substitution reaction.
an elimination reaction.
an addition reaction.
ANS:
d
11.
a.
b.
c.
d.
Refer to Exhibit 8-3. Hydroboration/oxidation of alkenes occurs with:
anti stereochemistry.
trans stereochemistry.
syn stereochemistry.
unpredictable stereochemistry.
ANS:
c
4
Chapter 8
12.
a.
b.
c.
d.
Refer to Exhibit 8-3. The regiochemistry of hydroboration/oxidation of alkenes is:
Markovnikov.
non-Markovnikov
subject to solvent effects.
unrelated to alkene structure.
ANS:
b
Exhibit 8-4
Consider the reaction below to answer the following question(s).
When dichlorocarbene is generated in the presence of an alkene, a dichlorocyclopropane is
formed.
13.
Refer to Exhibit 8-4. Write the complete stepwise mechanism for the formation of
dichlorocarbene, CCl2. Show all intermediate structures and show all electron flow with
arrows.
ANS:
14.
Refer to Exhibit 8-4. Draw the complete Lewis electron dot structure for dichlorocarbene,
CCl2.
ANS:
5
Alkenes: Reactions and Synthesis
15.
a.
b.
c.
d.
Refer to Exhibit 8-4. In the reaction of an alkene with dichlorocarbene, the dichlorocarbene
is the:
electrophile.
Lewis base.
nucleophile.
both b and c.
ANS:
a
16.
a.
b.
c.
d.
Refer to Exhibit 8-4. The reaction of an alkene with dichlorocarbene is:
regiospecific.
Markovnikov.
stereospecific.
non-Markovnikov.
ANS:
c
Exhibit 8-5
The sequence of (1) alkene hydroxylation followed by (2) diol cleavage is often an excellent
alternative to direct alkene cleavage with ozone. For this sequence below, answer the following
question(s).
17.
Refer to Exhibit 8-5. Draw the structure of A.
ANS:
18.
ANS:
HIO4
6
Refer to Exhibit 8-5. Give the formula for reagent B.
Chapter 8
Exhibit 8-6
Predict the products of each reaction below. Indicate regiochemistry and stereochemistry when
relevant.
19.
ANS:
20.
ANS:
21.
ANS:
7
Alkenes: Reactions and Synthesis
22.
ANS:
23.
ANS:
24.
ANS:
25.
ANS:
8
Chapter 8
26.
ANS:
27.
ANS:
28.
ANS:
29.
ANS:
9
Alkenes: Reactions and Synthesis
Exhibit 8-7
Choose the best reagent from the list below for carrying out each transformation. Place the letter of
the reagent in the blank to the left of the reaction.
a.
1.
2.
O3
Zn, H3O+
e.
1.
2.
b.
1.
2.
BH3, THF
H2O2, NaOH, H2O
f.
KMnO4, acid
c.
CHCl3, KOH
g.
CH2I2, Zn(Cu)
d.
H2O, H2SO4, heat
h.
1.
2.
30.
_____
ANS:
b
31.
_____
ANS:
a
32.
_____
ANS:
g
33.
ANS:
h
10
_____
OsO4
NaHSO3, H2O
Hg(OAc)2, H2O
NaBH4
Chapter 8
Exhibit 8-8
For each reaction below suggest structures for alkenes that give the indicated reaction products.
There may be more than one answer in some cases.
34.
ANS:
35.
ANS:
36.
ANS:
11
Alkenes: Reactions and Synthesis
37.
ANS:
CH2=CHC6C5
Exhibit 8-9
To answer the question(s) below consider the following information:
In an abandoned laboratory has been found a flammable liquid, A, in a bottle bearing only the
label "Compound A: C7H12." Government agents have offered you a considerable sum to
determine the structure of this compound. After verifying the molecular formula by elemental
analysis, you find that Compound A reacts with 1 mol equiv of hydrogen; and, after treatment with
acidic KMnO4, Compound A gives the dicarboxylic acid C (see below). Another bottle from the
same laboratory is labeled "Compound B (isomer of A)." Compound B also reacts with 1 mol
equiv of hydrogen, but yields cyclohexanone after treatment with acidic KMnO4.
38.
Refer to Exhibit 8-9. How many degrees of unsaturation does Compound A possess?
ANS:
A saturated seven carbon compound should have the formula C7H16 so compound A has (16  12)
 2 = 2 degrees of unsaturation.
39.
ANS:
12
Refer to Exhibit 8-9. Suggest structures for A and B.
Chapter 8
40.
Refer to Exhibit 8-9. What was the other product formed in the KMnO4 oxidation of B?
ANS:
CO2
41.
Lyapolate Sodium, whose structure is shown below, is used as an anticoagulant. Identify the
monomer unit(s) in lyapolate sodium.
ANS:
H2C=CHSO3Na
42.
Povidone is produced commercially as a series of products having mean molecular weights
ranging from about 10,000 to 700,000. Complexed with iodine, povidone yields an
iodophor, marketed under the tradename Betadine, which is used as a topical anti-infective.
Identify the monomer unit(s) in povidone.
ANS:
13
Alkenes: Reactions and Synthesis
43.
Draw the skeletal structure(s) and name the product(s) of the reaction when the following
substance is treated with sulfuric acid and warmed to approximately 50 °C. Atoms other
than hydrogen and carbon are labeled.
ANS:
Two products are possible.
Names respectively:
3-isopropyl-6-methylcyclohexene
1-isopropyl-4-methylcyclohexene
44.
14
Draw the skeletal structure(s) and name the product(s) of the reaction when the following
substance is treated with ethanoic KOH. Atoms other than hydrogen and carbon are labeled.
Chapter 8
ANS:
Two products are possible.
Names, respectively:
4,4-dimethylcyclopentene
3,3-dimethylcyclopentene
45.
Draw a condensed formula for a polymer containing five repeating units derived from the
following monomer. Name the polymer.
ANS:
polypropylene
46.
Consider the polymeric structure below for amylose (a type of starch). Draw a box around
the monomer of amylose. Extra: Propose a structure for the monomer. Hint: This polymer
is formed in a dehydration reaction.
15
Alkenes: Reactions and Synthesis
ANS:
47.
Consider the following polymer.
Draw the condensed formula for its monomer.
ANS:
48.
Hydration of 4-methyl-1-pentene in the presence of an acid catalyst produces a product that
is optically inactive. Briefly explain why.
ANS:
While hydration produces alcohols with a chiral center, the product is a racemic mixture. The
first step of the hydration reaction involves Markovnikov protonation of 4-methyl-1-pentene to
yield a planar, secondary carbocation. In the second step, water attacks the planar carbocation
from either the Re or Si face with equal probability to give a racemic mixture of protonated
alcohols. Deprotonation of the protonated alcohols produces a racemic, optically inactive mixture
of (R)- and (S)-4-methyl-2 pentanol.
16
Chapter 8
49.
Hydration of an alkene during enzyme catalysis in a biological system produces an optically
active product even through there is a potential to form a racemic mixture. Explain why this
occurs.
ANS:
Chemical catalysts do not provide a chiral environment in which a reaction can occur, enzymes
provide such an environment. During enzyme catalysis, the planar carbocation is held in the
chiral environment of the enzyme’s active site such that the Re and Si faces of the cation are
distinguishable. The attacking water molecule can approach only one face of the cation, resulting
in one transition state and one enantiomer in the product. The latter producing the observed
optical activity.
50.
Draw the product(s) of the reaction of (R)-3-chlorobutene with HBr. Indicate
stereochemistry.
ANS:
MULTIPLE CHOICE
1.
a.
Which of the following will produce only one product upon dehydration?
b.
c.
d.
e. b and d
17
Alkenes: Reactions and Synthesis
f. a, b, and c
g. None produce a single product.
ANS: E
2.
Consider the following intermediate.
Which is applicable to this structure?
a. results in anti stereochemistry
b. produces only the cis isomer
c. is called a bromohydrin
d. occurs during the addition of HBr
ANS: A
3.
Which of the following is a difference between hydroboration/oxidation and
oxymercuration?
a. conversion of an alkene to an alcohol
c. hydration
b. Markovnikov regiochemistry
d. heteroatom-containing intermediate
ANS: B
4.
Which of the following is a carbene?
a. R3C+
b. R:–
c. R2:
d. R.
ANS: C
5.
18
What product forms when the following substance is treated with chloroform in the presence
of KOH?
Chapter 8
a.
c.
b.
d.
ANS: D
6.
a.
Which of the following will not undergo catalytic reduction in the presence of H2 and metal
catalyst?
c.
b.
d.
ANS: D
7.
Hydrogenation reactions use a metal catalyst as depicted below.
Which of the following does not occur during such a reaction?
a. The metal provides a surface upon molecules can adsorb.
b.  bonds are involved in the interaction between the metal and the unsaturated
hydrocarbon.
c. Molecular hydrogen attacks the topside of the adsorbed hydrocarbon.
d. Hydrogen atoms are transferred to the carbon atoms of the multiple bond one at a time.
ANS: C
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Alkenes: Reactions and Synthesis
8.
a.
b.
c.
d.
In the formation of an addition polymer such as polyvinylchloride,
the monomers must have at least one degree of unsaturation.
the formation occurs via a polar reaction.
the products have the same degree of complexity as biopolymers.
the resulting polymer generally contains two types of monomer.
ANS: A
9.
Consider partial hydrogenation of the following substance.
Which of the following describes this reaction?
a. 4 moles of hydrogen would required.
b. The product would contain trans double bond(s).
c. The product would be saturated.
d. The product would lower blood cholesterol.
e. All of the above would occur.
ANS: B
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