OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
Chapter 8 – Alkenes: Reactions and Synthesis
Solutions to Problems
8.1
Dehydrobromination may occur in either of two directions to yield a mixture of products.
8.2
Five alkene products, including E, Z isomers, might be obtained by dehydration of 3-
methyl-3-hexanol.
8.3
The chlorines are trans to one another in the product, as are the methyl groups.
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8.4
Addition of hydrogen halides involves formation of an open carbocation, not a cyclic
halonium ion intermediate. The carbocation, which is sp2-hybridized and planar, can be
attacked by chloride from either top or bottom, yielding products in which the two methyl
groups can be either cis or trans to each other.
8.5
–Br and –OH are trans in the product.
8.6 Reaction of the alkene with Br2 (formed from NBS) produces a cyclic bromonium ion.
When this bromonium ion is opened by water, a partial positive charge develops at the
carbon whose bond to bromine is being cleaved.
Since a secondary carbon can stabilize this charge better than a primary carbon, opening of
the bromonium ion occurs at the secondary carbon to yield the Markovnikov product.
8.7 Keep in mind that oxymercuration is equivalent to Markovnikov addition of H2O to an
alkene.
(a)
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,OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
(b)
8.8 Think backwards to select the possible alkene starting materials for the alcohols pictured.
(a)
(b)
Oxymercuration occurs with Markovnikov orientation.
8.9 Hydroboration/oxidation occurs with non-Markovnikov regiochemistry to give products in
which –OH is bonded to the less highly substituted carbon.
(a)
(b)
8.10 As described in Worked Example 8.2, the strategy in this sort of problem begins with a
look backward. In more complicated syntheses this approach is essential, but even in
problems in which the functional group(s) in the starting material and the reagents are
known, this approach is effective.
All the products in this problem result from hydroboration/oxidation of a double bond. The
–OH group is bonded to the less substituted carbon of the double bond in the starting
material.
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, OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
(a)
(b)
This product can also result from oxymercuration of the starting material in (a).
(c)
8.11 The drawings below show the transition states resulting from addition of BH3 to the double
bond of the cycloalkene. Addition can occur on either side of the double bond.
Reaction of the two neutral alkylborane adducts with hydrogen peroxide gives two alcohol
isomers. In one isomer, the two methyl groups have a cis relationship, and in the other
isomer they have a trans relationship.
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Chapter 8 – Alkenes: Reactions and Synthesis
Solutions to Problems
8.1
Dehydrobromination may occur in either of two directions to yield a mixture of products.
8.2
Five alkene products, including E, Z isomers, might be obtained by dehydration of 3-
methyl-3-hexanol.
8.3
The chlorines are trans to one another in the product, as are the methyl groups.
1 8/9/2023
, OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
8.4
Addition of hydrogen halides involves formation of an open carbocation, not a cyclic
halonium ion intermediate. The carbocation, which is sp2-hybridized and planar, can be
attacked by chloride from either top or bottom, yielding products in which the two methyl
groups can be either cis or trans to each other.
8.5
–Br and –OH are trans in the product.
8.6 Reaction of the alkene with Br2 (formed from NBS) produces a cyclic bromonium ion.
When this bromonium ion is opened by water, a partial positive charge develops at the
carbon whose bond to bromine is being cleaved.
Since a secondary carbon can stabilize this charge better than a primary carbon, opening of
the bromonium ion occurs at the secondary carbon to yield the Markovnikov product.
8.7 Keep in mind that oxymercuration is equivalent to Markovnikov addition of H2O to an
alkene.
(a)
8/9/2023 2
,OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
(b)
8.8 Think backwards to select the possible alkene starting materials for the alcohols pictured.
(a)
(b)
Oxymercuration occurs with Markovnikov orientation.
8.9 Hydroboration/oxidation occurs with non-Markovnikov regiochemistry to give products in
which –OH is bonded to the less highly substituted carbon.
(a)
(b)
8.10 As described in Worked Example 8.2, the strategy in this sort of problem begins with a
look backward. In more complicated syntheses this approach is essential, but even in
problems in which the functional group(s) in the starting material and the reagents are
known, this approach is effective.
All the products in this problem result from hydroboration/oxidation of a double bond. The
–OH group is bonded to the less substituted carbon of the double bond in the starting
material.
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, OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
(a)
(b)
This product can also result from oxymercuration of the starting material in (a).
(c)
8.11 The drawings below show the transition states resulting from addition of BH3 to the double
bond of the cycloalkene. Addition can occur on either side of the double bond.
Reaction of the two neutral alkylborane adducts with hydrogen peroxide gives two alcohol
isomers. In one isomer, the two methyl groups have a cis relationship, and in the other
isomer they have a trans relationship.
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