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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 CH4 , 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 CH4 are identical, and the bond angles are equal (109.5°).
3.
The first ten normal alkanes:
CH4
methane
C2H6
ethane
C3H8
propane
C4H10
butane
C5H12
pentane
hexane
heptane
octane
nonane
decane
C6H14
C7H16
C8H18
C9H20
C10H22
A molecule of ethane, C2H6 , contains seven sigma bonds.
A molecule of butane, C4H10 , contains thirteen sigma bonds.
A molecule of 2-methylpropane also contains thirteen sigma bonds.
4.
(a)
(b)
(c)
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.
Iso used in the word isomers means compounds having the same molecular formula but
different structural formulas. Iso also refers to a particular isomer with a methyl branch at
the end of a carbon chain. For example, isopentane
CH 3CHCH 2CH 3
ƒ
CH 3
Sec-: a secondary carbon atom, one that is bonded to two other carbon atoms.
CH3CH2 CHCH3
ƒ
sec carbon atom
secondary butyl group
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Tert- or t-: a tertiary carbon atom. A carbon atom that is bonded to three other carbon
atoms as in tert-butyl group
CH3
ƒ
CH3C ¬ — tert carbon atom
ƒ
CH3
7.
(a)
(b)
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.
8.
Gasoline with a higher octane blocks too-rapid combustion in high compression
automobile engines.
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.
2.
Lewis structures:
≠C
¶l≠
•l≠C
•l≠
≠C
¶
¶≠C
¶
•l≠
≠C
¶
(a)
CCl 4
(c)
CH3CH2CH3
(b)
C2Cl 6
≠C
¶l≠≠C
¶l≠
•l≠C
•≠
≠C
¶
¶≠ C
¶ ≠Cl
¶
•l≠≠C
•l≠
≠C
¶
¶
(b)
C3H8
H H H
•≠C
•≠C
•≠H
H≠C
¶
¶
¶
H H H
H H H
•≠C
•≠C
•≠H
H≠C
¶
¶
¶
H H H
Lewis structures:
(a)
CH4
(c)
C5H12
H
•≠H
H≠C
¶
H
H H H H H
•≠C
•≠C
•≠C
•≠C
•≠H
H≠C
¶
¶
¶
¶
¶
H H H H H
3.
Formulas (a) and (i) are not isomers. They are the same compound.
Formulas (b) and (c) are isomers of C5H12 .
Formulas (f) and (h) are isomers of C5H10 .
Formulas (d), (e), and (g) are isomers of C6H14 .
4.
Formulas (b), (e), and (f) are identical. The others are different.
5.
The formulas in Exercise 3 contain the following numbers of methyl groups:
(a) 2
(b) 2
(c) 3
(d) 2
(e) 4
(f) 0
(g) 3
(h) 1
(i) 2
6.
The formulas in Exercise 4 contain the following numbers of methyl groups:
(a) 4
(b) 4
(c) 4
(d) 4
(e) 4
(f) 4
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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
CH3
CH 3
ƒ
ƒ
CH3CH2CCH3
CH 3CHCHCH 3
ƒ
ƒ
CH3
CH 3
CH2Cl 2 , one
CH2Cl 2
CH3CHBrCH3
C3H7Br, two
CH3CH2CH2Br
CH3CHClCH2Cl
C3H 6Cl 2 , four
CH3CH2CHCl 2
CH2ClCH2CH2Cl
CH3CCl 2CH3
CH3CH2CHClCH2Cl
C4H8Cl 2 , nine
CH3CH2CH2CHCl 2
CH3CHClCH2CH2Cl
CH2ClCH2CH2CH2Cl
CH3CH2CCl 2CH3
CH3CHCH2Cl 2
CH3CHCH2Cl
CH3CClCH2Cl
CH3CHClCHClCH3
ƒ
ƒ
ƒ
CH2Cl
CH3
CH3
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10.
(a)
(b)
(c)
(d)
CH3Br
CH3Br, one
CH3CH2Cl
C2H5Cl, one
C4H9I four
CH3CH2CH2CH2I
CH3CH2CHICH3
CH3CICH3
CH3CHCH2I
ƒ
ƒ
CH3
CH3
CH3CHClCH2Br
C3H 6Br Cl, five
CH 3CH 2CHBr Cl
CH 3CHBr CH 2Cl
CH2ClCH2CH2Br
CH 3CBr ClCH 3
11.
(a)
(b)
(c)
5 carbon atoms
5 carbon atoms
6 carbon atoms
12.
(a)
(b)
(c)
7 carbon atoms
7 carbon atoms
6 carbon atoms
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
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15.
CH3
(a)
CH3
CH
CH3
CH
CH2
CH3
CH3
CH3
CH
(b)
CH3
CH2
C
CH2
CH3
CH3
CH3
(c)
CH3
C
CH3
CH3
CH2
C
CH2
CH3
CH
CH2
CH3
CH3
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16.
(a)
(b)
H3C
CH
CH2
CH
CH3
CH3
CH
CH2
CH2
CH2
CH3
CH3
CH
CH3
CH3
CH3
CH2
C
CH2
CH3
CH3
CH3
(c)
CH3
17.
CH3
C
CH2
CH
CH3
CH3
Structural formulas:
(a)
(b)
(c)
(d)
CH3
CH3
ƒ
ƒ
2,4-dimethylpentane
CH3CH CH2CHCH3
CH 3
ƒ
2, 2-dimethylpentane
CH 3CCH 2CH 2CH 3
ƒ
CH 3
3-isopropyloctane
CH 3CH 2CHCH 2CH 2CH 2CH 2CH 3
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
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(e)
2-ethyl- 1,3-dimethylcyclohexane
CH3
CH2CH3
CH3
18.
(a)
(b)
(c)
(d)
(e)
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
CH3 CH2CH3
ƒ
ƒ
CH3 ¬ C ¬ CHCH2CH2CH2CH2CH3
3-ethyl-2,2-dimethyloctane
ƒ
CH3
1,3-diethylcyclohexane
CH2CH3
CH2CH3
19.
(a)
CH3
ƒ
CH3CH2CHCH3
3-methylbutane
Numbering was done from the wrong end of the molecule. The correct name is
2-methylbutane.
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(b)
(c)
(d)
CH3CHCH2CH3
ƒ
CH2CH3
The name is not based on the longest carbon chain (5 carbons). The correct name is 3methylpentane.
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
2-ethylbutane
CH3
CH3
The ring was numbered in the wrong direction. The correct name is
1,3-dimethylcyclopentane.
20.
(a)
(b)
(c)
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
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 3,5diethyl-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.
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(d)
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
CH3CHCHClCH2Cl
CH3CClCH2CH2Cl
CH3
ƒ
CH2ClCHCH2CH2Cl
CH3
ƒ
CH3CHCCl 2CH3
CH3
ƒ
CH2ClCHCHClCH3
CH3
ƒ
CHCl 2CHCH2CH3
CH3
ƒ
CH3CClCHClCH3
CH3
ƒ
CH2ClCClCH2CH3
CH 2Cl
ƒ
CH 2ClCHCH 2CH 3
22.
CH3CH2CH2CH2CH2CH2Cl
CH 3CH 2CH 2CH 2CHClCH 3
CH3CH2CH2CHClCH2CH3
23.
24.
25.
hv
(a)
CH 3CH 2CH 2CH 3 + Cl 2
(b)
2 CH 3CH 2CH 2CH 3 + 13 O2
(a)
CH3CH2CH3 + Br2
(b)
CH 3CH 2CH 3 + 5 O2
hv
" CH CH CHClCH + CH CH CH CH Cl + HCl
3
2
3
3
2
2
2
¢
" 8 CO + 10 H O
2
2
" CH CH CH Br + CH CHBrCH + HBr
3
2
2
3
3
¢
" 3 CO + 4 H O
2
2
Names:
(a) 1-chloro-2-ethylcyclohexane
(b) 1-chloro-3-ethyl-l-methylcyclohexane
(c) 1,4-diisopropylcyclohexane
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26.
Structural formulas:
(a)
CH
CH3
3
H3C
(b)
C
C CH3
CH3
CH3
CH3
CH2CH2CH3
(c)
Cl
CH2CH3
CH3 ¬ H2C
Cl
27.
One isomer: CH3CH(CH3)CH2CH3
28.
One isomer: CH3C(CH3)2CH2CH3
29.
(a)
CH3CH(CH3)CH2CH2CH(CH3)CH3 , 2,5-dimethylhexane
CH3
CH3
30.
(b)
1,2-dimethylcyclohexane
(a)
(b)
CH3C(CH3)2CH3, 2,2-dimethylpropane
CH3CH2CH2CH2CH3 , pentane
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31.
(a)
(b)
Five isomers:
H
H
ƒ
ƒ
CH2Cl ¬ C ¬ CH2 ¬ CH2 ¬ CH3
CH3 ¬ C ¬ CH2 ¬ CHCl ¬ CH3
ƒ
ƒ
CH3
CH3
2-chloro-4-methylpentane
1-chloro-2-methylpentane
H
ƒ
CH3 ¬ CClCH2 ¬ CH2 ¬ CH3
CH 3 ¬ C ¬ CH 2 ¬ CH 2 ¬ CH 2Cl
ƒ
ƒ
CH3
CH 3
1-chloro-4-methylpentane
2-chloro-2-methylpentane
H
ƒ
CH3 ¬ C ¬ CHCl ¬ CH2 ¬ CH3
ƒ
CH3
3-chloro-2-methylpentane
Five isomers:
CH2Cl
CH3
Cl
chloromethylcyclohexane
CH3
Cl
1-chloro-1-methylcyclohexane
2-chloro-1-methylcyclohexane
CH3
CH3
Cl
Cl
3-chloro-1-methylcyclohexane
4-chloro-1-methylcyclohexane
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32.
(a)
Three isomers:
Br
Br
Br
Br
Br
Br
1,1-dibromocyclopentane
(b)
1,2-dibromocyclopentane
Seven isomers:
CH3
ƒ
CHBr2 ¬ C ¬ CH2 ¬ CH3
ƒ
CH3
1,1-dibromo-2,2-dimethylbutane
CH3
ƒ
H3C ¬ C ¬ CH2 ¬ CHBr2
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
1,3-dibromocyclopentane
CH3
ƒ
H3C ¬ C ¬ CBr2 ¬ 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
33.
Each carbon of cyclohexane has bond angles of about 109° (forming a tetrahedran). 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
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36.
1gal
Data: 60 mi ; 60 mi traveled;
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
38.
(a)
(b)
(c)
elimination
substitution
addition
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.
Propane is the most volatile. Volatility: propane 7 butane 7 hexane
41.
(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.
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42.
(a)
Initiation:
Cl2
uv
2Cl
Propagation: Cl + CH4
CH3Cl + HCl
CH3 + Cl2
Termination: Cl + Cl
CH3Cl + Cl
Cl2
CH3 + CH3
CH3CH3
CH3 + Cl
(b)
Initiation:
Cl2
uv
CH3Cl
2Cl
Propagation: Cl + CH3CHCH3
(CH3)3C + HCl
CH3
(CH3)3C + Cl2
Termination: Cl + Cl
(CH3)3CCl + Cl
Cl2
(CH3)3C + (CH3)3C
(CH3)3C + Cl
(c)
uv
Initiation:
Cl2
Propagation:
Cl +
(CH3)3CCl
2Cl
+ HCl
Cl
+ Cl2
Termination:
Cl + Cl
(CH3)3CC(CH3)3
+ Cl
Cl2
+
+ Cl
Cl
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(d)
uv
Initiation:
Cl2
Propagation:
Cl +
2Cl
CH3
CH3
Termination: Cl + Cl
CH3
CH3
CH3
+ Cl2
+
Cl
+ Cl
Cl2
CH3
CH3
CH3
CH3
+ Cl
Cl
43.
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.
44.
(a)
(b)
(c)
(d)
sp3 hybrid orbitals in carbon.
Structural isomers are not possible because only one carbon atom is present.
dichlorodifluromethane
The closest classification for Freon-12 (CF2Cl 2) in Table 19.1 is alkyl halide.
45.
(a)
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3 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 .
(b)
46.
CH3
H 3C
1,3,5-trimethylcyclopentane is an incorrect name of this compound.
Numbering the ring counterclockwise gives the correct name,
1,2,4-trimethylcyclopentane.
CH3
47.
A mixture. A hydrocarbon of the formula, C4H10 , can have two possible structures:
(I) CH3CH2CH2CH3 and (II) CH3CH(CH3)CH3 .
Structure I can form only two monobromo compounds:
CH 2Br CH 2CH 2CH 3 and CH 3CHBr CH 2CH 3
Structure II can form only two monobromo compounds:
CH 2Br CH(CH 3)CH 3 . and CH3CBr(CH3)CH3 .
A mixture of the two structures gives four monobromo compounds.
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