HW Chapter 8th Answer Key
SHORT ANSWER
Section 7-1
Calculate the degree of unsaturation in each formula below. Show your calculations.
1.
pinene, C10H18
ANS:
The saturated ten carbon compound would have 22 hydrogens so the number of degrees of
unsaturation is: (22 − 18) ÷ 2 = 4 ÷ 2 = 2.
2.
eicosapentaenoic acid, C20H30O2, a constituent of fish oil
ANS:
Oxygen does not affect the base formula which in this case is C20H30. The saturated 20 carbon
compound would have 42 hydrogens so the number of degrees of unsaturation for
eiscosapentaenoic acid is: (42 − 30) ÷ 2 = 12 ÷ 2 = 6.
3.
diazepam (Valium), C16H13N2OCl
ANS:
Oxygen does not affect the base formula. A hydrogen is added to the base formula for each
halogen and subtracted for each nitrogen so the base formula for diazepam is C16H12. The saturated
16 carbon compound would have 34 hydrogens so the number of degrees of unsaturation for
diazepam is: (34 − 12) ÷ 2 = 22 ÷ 2 = 11.
Section 7-2
Dieldrin, C12H8Cl6O, is a pentacyclic compound formerly used as an insecticide.
4.
Refer to Section 7-2. Calculate the degree of unsaturation for Dieldrin. Show calculations
for credit.
ANS:
Oxygen does not affect the base formula. A hydrogen is added to the base formula for each
halogen so the base formula for dieldrin is C12H14. The saturated 12 carbon compound would have
26 hydrogens so the number of degrees of unsaturation for dieldrin is (26 − 14) ÷ 2 = 12 ÷ 2 = 6.
5.
Refer to Section 7-2. How many double bonds does dieldrin have?
ANS:
Dieldrin has 6 degrees of unsaturation and it is pentacyclic, meaning it has 5 rings. Therefore,
dieldrin must have one double bond.
1
Alkenes: Structure and Reactivity
Drawing Instructions: Draw structures corresponding to each name below. Either condensed or
line structures may be used.
6.
Draw: (3E)-3,7-dimethyl-1,3,6-octatriene
ANS:
7.
Draw: 3,6-dimethyl-1,4-cyclohexadiene
ANS:
8.
Draw: cis-2-hexene
ANS:
9.
ANS:
2
Draw: trans-4,4-dimethyl-2-pentene
Chapter 7
Section 7-4
2-Pentene is an example of a disubstituted alkene.
CH3CH=CHCH2CH3
10.
a.
b.
Refer to Section 7-4.
Draw the cis and trans isomers of 2-pentene and label them.
Circle the isomer which is most stable.
ANS:
a.
b.
11.
Section 7-5
Provide names for each structure below. Be sure to include the cis, trans or E, Z designations
where applicable.
12.
Name:
ANS:
trans-2-methyl-3-hexene or (E)-2-methyl-3-hexene
3
Alkenes: Structure and Reactivity
13.
Name:
ANS:
3-methylcyclopentene
14.
Name:
ANS:
(2E,4E)-5-ethyl-6-methyl-2,4-heptadiene
15.
Name:
ANS:
cis-3,3-dimethyl-4-propyl-1,5-octadiene or (Z)-3,3-dimethyl-4-propyl-1,5-octadiene
Section 7-6
Rank each set of substituents using the Cahn-Ingold-Prelog sequence rules by numbering the
highest priority substituent 1 and numbering the lowest priority substituent 4. Place the number in
the blank below the substituent.
16.
ANS:
4
Chapter 7
17.
ANS:
18.
ANS:
19.
ANS:
Section 7-7
MATCH each alkene below with the appropriate heat of hydrogenation. Place the letter of the
correct answer in the blank to the left of the alkene.
a.
b.
c.
125.9 kJ/mol
118.4 kJ/mol
115.5 kJ/mol
20.
______
ANS:
c
5
Alkenes: Structure and Reactivity
21.
______
ANS:
a
22.
______
ANS:
b
23.
a.
b.
c.
d.
Arrange the following bicyclic alkenes in order of increasing stability (least stable to most
stable).
III < II < I
I < II < III
I < III < II
II < III < I
ANS:
d
Section 7-8
Assign E or Z configurations to each alkene below.
24.
ANS:
Z
6
Chapter 7
25.
ANS:
E
26.
ANS:
E
Section 7-9
MATCH each definition to the term it describes. Place the letter corresponding to the term in the
blank to the left of the definition.
a.
b.
c.
Hammond Postulate
Cahn-Ingold-Prelog Rules
Markovnikov's Rule
27.
______ Predicts that the more stable carbocation intermediate is formed in electrophilic
additions to alkenes.
ANS:
c
28.
______ Predicts that the transition state of an exergonic reaction step structurally resembles
the reactant.
ANS:
a
29.
______ Assigns priorities to the substituent groups on a carbon.
ANS:
b
7
Alkenes: Structure and Reactivity
30.
______ Predicts that the transition state of an endergonic reaction step structurally resembles
the product.
ANS:
a
31.
_____ Predicts that in additions of HX to alkenes, the H adds to the less substituted alkene
carbon and the X adds to the more substituted alkene carbon.
ANS:
c
32.
Rank the carbocations below in order of increasing stability (least stable = 1; most stable =
3). Place the number corresponding to the carbocation's relative stability in the blank below
the structure.
ANS:
Section 7-10
Consider the following reaction:
33.
ANS:
8
Refer to Section 7-10. Write the complete stepwise mechanism for this reaction. Show all
intermediate structures and show all electron flow using the curved arrow convention.