CHAPTER 19
ORGANIC CHEMISTRY: SATURATED HYDROCARBONS
SOLUTIONS TO REVIEW QUESTIONS
1.
Two of the major reasons for the large number of organic compounds is the ability of
carbon to form short or very long chains of atoms covalently bonded together and
isomerism.
2.
The carbon atom has only two unshared electrons, making two covalent bonds logical, but
in
carbon forms four equivalent bonds. Promoting one 2s electron to the empty 2p
orbital would make four bonds possible, but without hybridization, we could not explain the
fact that all four bonds in
are identical, and the bond angles are equal (109.5°).
3.
The first ten normal alkanes:
C 4
methane
ethane
CH
propane
C4 10
butane
pentane
hexane
heptane
octane
nonane
decane
C6H14
C7H16
C8H18
C9H20
C10H22
4.
Aromatic hydrocarbons contain benzene rings. “Aliphatic” refers to all other
hydrocarbons including alkanes, alkenes, alkynes, and cycloalkanes.
5.
Advantages: Some freons have low boiling points and therefore are excellent refrigerants.
They are stable, nontoxic, nonflammable and noncorrosive.
Disadvantages: Freons are a major factor in the destruction of the ozone layer once they
get into the stratosphere.
6.
Cyclopropane is more reactive than cyclohexane because cyclopropane’s carbon–carbon
bond angles are substantially different from the normal tetrahedral angle.
7.
(a)
(b)
8.
A substitution reaction allows an exchange of atoms or groups of atoms between
reactants while in an elimination reaction a single reactant is split into two products.
Two reactants combine together in an addition reaction while one reactant is split
into two products in an elimination reaction.
Alkanes are hydrocarbons containing only the elements hydrogen and carbon. Alkyl
halides also contain halogens and, thus, can not be classified as alkanes.
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- Chapter 19 -
9.
E85 is a gasoline that contains 85% ethanol and 15% petroleum. This mixture reduces the
use of petroleum, a nonrenewable resource. E85 is the cleanest burning gasoline now
available.
10.
A major advantage of using plants like guayule or sunflower is that they are a renewable
source of hydrocarbons. This would cut down the use of petroleum for combustible
hydrocarbons.
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- Chapter 19 -
SOLUTIONS TO EXERCISES
1.
Lewis structures:
(a)
(c)
2.
4
≠C
C
¶l≠
• ¶¶
•
¶
•
≠C
¶l≠
CH3CH2CH3
(b)
C2Cl 6
≠C
C
C
¶l≠
¶l≠≠C
•
•
Cl
≠C
¶l≠C
¶≠ C
¶ ≠C
¶≠
•
•
≠C
¶l≠≠C
¶l≠
C3H8
H H H
•≠C
•
•
H≠C
¶≠C
¶≠H
¶
H H H
H H H
•
•
•
H≠C
¶≠C
¶≠C
¶≠H
H H H
Lewis structures:
(a)
(c)
4
C5H12
H
•
¶
H
(b)
H H H H H
•≠C
•≠C
•≠C
•
•
H≠C
¶
¶≠C
¶
¶
¶≠H
H H H H H
3.
The formulas (a), (c), (f), and (g) represent isomers.
4.
The same compound is represented by formulas (a), (c), and (f).
5.
The number of methyl groups in each formula in Exercise #3 is as follows:
(a) 2 (b) 2 (c) 3 (d) 4 (e) 1 (f) 3 (g) 4 (h) 3
6.
The number of methyl groups in each formula in Exercise #4 is as follows:
(a) 3 (b) 2 (c) 3 (d) 4 (e) 4 (f) 3
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- Chapter 19 -
7.
Isomers of heptane
CH3CH2CH2CH2CH2CH2CH3
CH3CH2CH2CHCH2CH3
ƒ
CH3
CH 3
ƒ
CH 3CH 2CHCHCH 3
ƒ
CH 3
CH3CH2CH2CH2CHCH3
ƒ
CH3
CH3
ƒ
CH3CH2CH2CCH3
ƒ
CH3
CH 3CHCH 2CHCH 3
ƒ
ƒ
CH 3 C H 3
CH 3
ƒ
CH 3CH 2CCH 2CH 3
ƒ
CH 3
CH3 CH3
ƒ
ƒ
CH3CH ¬ CCH3
ƒ
CH3
CH3CH2CHCH2CH3
ƒ
CH2CH3
8.
Isomers of hexane
CH3CH2CH2CH2CH2CH3
CH3CH2CHCH2CH3
ƒ
CH3
9.
(a)
(b)
(c)
(d)
CH3CH2CH2CHCH3
ƒ
CH3
CH 3
CH3
ƒ
ƒ
CH3CH2CCH3
CH 3CHCHCH 3
ƒ
ƒ
CH 3
CH3
l 2 one
CH2Cl 2
two
CH3CH2CH2Br
CH3CHBrCH3
3 7
CH3CHClCH2Cl
CH3CH2CHCl 2
3 6 2 four
CH2ClCH2CH2Cl
CH3CCl 2CH3
CH3CH2CH2CHCl 2
CH3CH2CHClCH2Cl
4 8 2 nine
CH3CHClCH2CH2Cl
CH2ClCH2CH2CH2Cl
CH3CH2CCl 2CH3
CH3CHCH2Cl
CH3CHCH2Cl 2
CH3CClCH2Cl
CH3CHClCHClCH3
ƒ
ƒ
ƒ
CH2Cl
CH3
CH3
2
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- Chapter 19 -
10.
(a)
(b)
(c)
(d)
one
CH3Br
one
CH3CH2Cl
2 5
CH3CH2CH2CH2I
CH3CH2CHICH3
4 9 , four
CH3CHCH2I
CH3CICH3
ƒ
ƒ
CH3
CH3
five
CH 3CH 2CHBr Cl
CH3CHClCH2Br
3 6
CH 3CHBr CH 2Cl
CH2ClCH2CH2Br
CH 3CBrClCH 3
3
11.
(a)
5
(b) 6
(c)
5
12.
(a) 7
(b) 7
(c)
6
13.
IUPAC names
(a) 1-chloropropane
(b) 2-chloropropane
(c) 2-chloro-2-methylpropane
(d) 2-methylbutane
(e) 2,3-dimethylhexane
14.
IUPAC names
(a) chloroethane
(b) 1-chloro-2-methylpropane
(c) 2-chlorobutane
(d) methylcyclopropane
(e) 2,4-dimethylpentane
15.
The tertiary carbons are circled in the following structures from Exercise #11:
CH 3
CH 3
(a)
C
CH 3
CH 3 CHCHCH2 CH 3
CH 3
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- Chapter 19 -
CH 2 CH 3
(b)
CH 3 CHCHCH3
CH 2CH 3
CH 3 CH 3 CH 3
(c)
CH 3 C
C
C
CH 3
CH 3 CH 3 CH 3
16.
The tertiary carbons are circled in the following structures from Exercise #12:
CH 2 CH 3
CH 3 CHCHCH 3
(a)
CH 2 CH
CH 3
CH 3
CH 2 CH 2 CH 3
(b)
CH 3 C
CH 2 CH 3
CH 2 CH 2 CH 3
CH 3 CHCH 2 CH 3
(c)
CH 3 C
CH 3
CH 2 CH 3
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- Chapter 19 -
17.
Structural formulas:
(a)
(b)
(c)
(d)
(e)
CH3
CH3
ƒ
ƒ
CH3CH CH2CHCH3
2,4-dimethylpentane
CH 3
ƒ
2, 2-dimethylpentane
CH 3CCH 2CH 2CH 3
ƒ
CH 3
CH 3CH 2CHCH 2CH 2CH 2CH 2CH 3
3-isopropyloctane
ƒ
C H(CH 3)2
5,6-diethyl-2,7-dimethyl-5-propylnonane
CH 3
CH 2CH 3
CH 3
ƒ
ƒ
ƒ
CH 3CH CH 2CH 2C ¬¬ CH ¬¬ CHCH 2CH 3
ƒ
ƒ
CH 3CH 2CH 2 CH 2CH 3
2-ethyl-1,3-dimethylcyclohexane
CH3
CH2CH3
CH3
18.
(a)
(b)
(c)
CH 3
ƒ
CH 3CH 2CHCH 2CHCH 3
4-ethyl-2-methylhexane
ƒ
CH 2CH 3
CH3CH2CH2CHCH2CH2CH3
4-t-butylheptane
ƒ
C(CH3)3
4-ethyl-7-isopropyl-2,4,8-trimethyldecane
CH 3
ƒ
CH 3 CH 2CH 3 CHCH 3
ƒ
ƒ
ƒ
CH 3CHCH 2CCH 2CH 2CHCHCH 2CH 3
ƒ
ƒ
CH 3
CH 3
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- Chapter 19 -
(d)
3-ethyl-2,2-dimethyloctane
(e)
1,3-diethylcyclohexane
CH3 CH2CH3
ƒ
ƒ
CH3 ¬ C ¬ CHCH2CH2CH2CH2CH3
ƒ
CH3
CH2CH3
CH2CH3
19.
(a)
(b)
(c)
(d)
CH3
ƒ
CH3CH2CHCH3
3-methylbutane
Numbering was done from the wrong end of the molecule. The correct name is
2-methylbutane.
CH3CHCH2CH3
2-ethylbutane
ƒ
CH2CH3
The name is not based on the longest carbon chain (5 carbons). The correct name is
3-methylpentane.
2-dimethylpentane. Each methyl group needs to be numbered. Depending on the
structure, the correct name is 2,2-dimethylpentane; 2,3-dimethylpentane; or
2,4-dimethylpentane.
1,4-dimethylcyclopentane
CH3
CH3
The ring was numbered in the wrong direction. The correct name is
1,3-dimethylcyclopentane.
20.
(a)
CH3CH2CHCH2CHCH2CH2CH3
ƒ
ƒ
CH3 CH2CH3
Ethyl should be named before methyl (alphabetical order). The numbering is
correct. The correct name is 5-ethyl-3-methyloctane.
3-methyl-5-ethyloctane
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- Chapter 19 -
(b)
(c)
(d)
3,5,5-triethylhexane
CH 2CH 3
ƒ
CH 3CH 2CHCH 2CCH 3
ƒ
ƒ
CH 2 CH 2CH 3
ƒ
CH 3
The name is not based on the longest carbon chain (7 carbons). The correct name is
3,5-diethyl-3-methylheptane.
4,4-dimethyl-3-ethylheptane
CH 3
ƒ
CH 3CH 2CH¬ CCH 2CH 2CH 3
ƒ
ƒ
CH 3CH 2 CH 3
Ethyl should be named before dimethyl (alphabetical order). The correct name is
3-ethyl-4,4-dimethylheptane.
1,6-dimethylcyclohexane
CH3
CH3
The ring was numbered in the wrong direction. The correct name is
1,2-dimethylcyclohexane.
21.
Structures for the ten dichlorosubstituted isomers of 2-methylbutane:
CH3
CH3
CH3
ƒ
ƒ
ƒ
CH3CHCH2CHCl 2
CH3CClCH2CH2Cl
CH3CHCHClCH2Cl
CH3
ƒ
CH2ClCHCH2CH2Cl
CH3
ƒ
CH3CHCCl 2CH3
CH3
ƒ
CH2ClCHCHClCH3
CH3
ƒ
CHCl 2CHCH2CH3
CH 2Cl
ƒ
CH 2ClCHCH 2CH 3
- 269 -
CH3
ƒ
CH3CClCHClCH3
CH3
ƒ
CH2ClCClCH2CH3
- Chapter 19 -
22.
CH3CH2CH2CH2CH2CH2Cl
CH 3CH 2CH 2CH 2CHClCH 3
CH3CH2CH2CHClCH2CH3
23.
One isomer: CH3CH(CH3)CH2CH3
24.
One isomer: CH3C(CH3)2CH2CH3
25.
(a) 2-chlorobutane
26.
(a) 2-bromo-2,3-dimethylbutane
27.
(a)
(b)
(b) 2-chloro-2-methylpropane
(b) 2-bromo-2-methylbutane
2,5-dimethylhexane
CH3
1,2-dimethylcyclohexane
CH3
28.
(a)
(b)
29.
(a)
2,2-dimethylpropane
pentane
Five isomers:
H
H
ƒ
ƒ
CH3 ¬ C ¬ CH2 ¬ CHCl ¬ CH3
CH2Cl ¬ C ¬ CH2 ¬ CH2 ¬ CH3
ƒ
ƒ
CH3
CH3
2-chloro-4-methylpentane
1-chloro-2-methylpentane
H
ƒ
CH 3 ¬ C ¬ CH 2 ¬ CH 2 ¬ CH 2Cl
3 ¬ CClCH2 ¬ CH2 ¬ CH3
ƒ
ƒ
CH3
CH 3
1-chloro-4-methylpentane
2-chloro-2-methylpentane
H
CH 3
C
CHCl
CH2
CH 3
3-chloro-2-methylpentane
- 270 -
CH 3
- Chapter 19 -
(b)
Five isomers:
CH2Cl
CH3
Cl
chloromethylcyclohexane
CH3
Cl
1-chloro-1-methylcyclohexane
2-chloro-1-methylcyclohexane
CH3
CH3
Cl
Cl
3-chloro-1-methylcyclohexane
30.
(a)
4-chloro-1-methylcyclohexane
Three isomers:
Br
Br
Br
Br
Br
Br
1,1-dibromocyclopentane
1,2-dibromocyclopentane
- 271 -
1,3-dibromocyclopentane
- Chapter 19 -
(b)
Seven isomers:
CH3
ƒ
CHBrr2 ¬ C ¬ CH2 ¬ CH3
ƒ
CH3
1,1-dibromo-2,2-dimethylbutane
CH3
ƒ
H3C ¬ C ¬ CH2 ¬ CHBrr2
ƒ
CH3
1,1-dibromo-3,3-dimethylbutane
CH3
ƒ
CH2Br ¬ C ¬ CHBr ¬ CH3
ƒ
CH3
1,3-dibromo-2,2-dimethylbutane
CH3
ƒ
H3C ¬ C ¬ CHBr ¬ CH2Br
ƒ
CH3
1,2-dibromo-3,3-dimethylbutane
CH3
ƒ
H3C ¬ C ¬ CBrr2 ¬ CH3
ƒ
CH3
3,3-dibromo-2,2-dimethylbutane
CH 2Br
ƒ
CH 2Br ¬ C ¬ CH 2 ¬ CH 3
ƒ
CH 3
1-bromo-2-bromomethyl-2-methylbutane
CH3
ƒ
CH2Br ¬ C ¬ CH2 ¬ CH2Br
ƒ
CH3
1,4-dibromo-2,2-dimethylbutane
31.
Names:
(a) 1-chloro-2-ethylcyclohexane
(b) 1-chloro-3-ethyl-l-methylcyclohexane
(c) 1,4-diisopropylcyclohexane
32.
Structural formulas:
(a)
CH3
H3C
CH3
C
C CH3
CH3
CH3
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- Chapter 19 -
(b)
CH3
CH2CH2CH3
(c)
Cl
CH2CH3
CH3 ¬ H2C
Cl
33.
Each carbon of cyclohexane has bond angles of about 109° (forming a tetrahedron). Thus,
when these carbons are bonded together, the ring cannot be flat.
34.
The formula for dodecane is C12H26 .
35.
FCH2CH2F + Cl 2 ¡ FCH2CHClF + HCl
36.
Data: 60 mi 60 mi traveled;
1gal
19 mol C8H 18
gal
; T= 293K
2 C8H 18 + 25 O2 ¡ 16 CO2 + 18 H 2O
1 gal
60 mi
* 60 mi = 1 gal gasoline used
19 mol C8H 18 *
37.
= 1.5 * 102 mol CO2
nRT
P
(1.5 * 102 mol CO2)(0.0821 L-atm)(293K)
1 atm
mol-K
PV = nRT
V =
16 mol CO2
2 mol C8H 18
V =
= 3.6 * 103 L CO2
Cycloalkanes with formulas C5H10
CH3
cyclopentane
methylcyclobutane
CH3
CH3
1,1-dimethylcyclopropane
CH2CH3
ethylcyclopropane
CH3
H3C
1,2-dimethylcyclopropane
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- Chapter 19 -
elimination
substitution
addition
38.
(a)
(b)
(c)
39.
It is not possible to distinguish hexane from 3-methylheptane based on solubility in water
because both compounds are nonpolar and, thus, insoluble in water.
40.
(a)
(b)
(c)
(d)
The compounds are isomers.
The compounds are not the same and are not isomers.
The compounds are not the same and are not isomers.
The compounds are not the same and are not isomers.
41.
(a)
Initiation:
Cl2
uv
2 Cl
Propagation: Cl + CH4
CH3Cl + HCl
CH3 + Cl2
Termination: Cl + Cl
CH3Cl + Cl
Cl2
CH3 + CH3
CH3CH3
CH3 + Cl
(b)
Initiation:
Cl2
uv
CH3Cl
2 Cl
Propagation: Cl + CH3CHCH3
(CH3)3C + HCl
CH3
(CH3)3C + Cl2
Termination: Cl + Cl
(CH3)3CCl + Cl
Cl2
(CH3)3C + (CH3)3C
(CH3)3C + Cl
(CH3)3CC(CH3)3
(CH3)3CCl
- 274 -
- Chapter 19 -
(c)
uv
Initiation:
Cl2
Propagation:
Cl +
2 Cl
+ HCl
Cl
+ Cl2
Termination:
Cl + Cl
+ Cl
Cl2
+
Cl
+ Cl
(d)
uv
Initiation:
Cl2
Propagation:
Cl +
2 Cl
CH3
CH3
CH3
CH3
+ Cl2
Termination: Cl + Cl
CH3
CH3
Cl
+ HCl
+ Cl
Cl2
CH3
CH3
+
CH3
CH3
+ Cl
Cl
42.
Using a high mole ratio of methane to chlorine will allow a chlorine free radical to react
with a methane molecule rather than a chloromethane molecule and minimize the
formation of di-, tri-, and tetrachloromethane.
43.
(a)
(b)
44.
undecane
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3 tridecane
Both compounds are alkanes. They are composed of only carbon and hydrogen and
have only single bonds between the carbon atoms. Both formulas agree with the
general formula for alkanes, CnH2n+2 .
3
2
2
2
2
2
2
2
2
2
3
Cyclopentane and cycloheptane are in the same homologous series (cycloalkanes) and
share the same general formula, CnH2n. The formula for cycloheptane is C7H14.
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- Chapter 19 -
F
45.
(a)
R-32 F
C
H
(b)
H
R-125 H
F
F
C
C
F
F
F
R-134a H
H
F
C
C
F
F
R-32, four sigma bonds; R-125, seven sigma bonds; R-134a, seven sigma bonds.
46.
(a) 2-methylpentane;
47.
(a)
(b) 2,4-dimethylheptane;
(c) 4-ethyl-3-methyloctane.
(b)
48.
A mixture. A hydrocarbon of the formula,
can have two possible structures:
(I)
3
2
2
3 and (II) CH3CH(CH3)CH3 .
Structure I can form only two monobromo compounds:
CH 2BrCH 2CH 2CH 3 and CH 3CHBrCH 2CH 3
Structure II can form only two monobromo compounds:
CH 2BrCH(CH 3)CH 3 . and CH3CBr(CH3)CH3 .
A mixture of the two structures gives four monobromo compounds.
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F