Chapter 12 Alkanes - websites.rcc.eduwebsites.rcc.edu/grey/files/2012/02/Chapter-12-Solutions-Smith.pdf · Chapter 12–1 Chapter 12 Alkanes Solutions to In -Chapter Problems 12.1

Chapter 12–1

Chapter 12 Alkanes Solutions to In-Chapter Problems 12.1 • An acyclic alkane has the molecular formula CnH2n + 2, where n is the number of carbons it

contains. • A cycloalkane has two fewer H’s than an acyclic alkane with the same number of carbons, and

its general formula is CnH2n.

a. An acyclic alkane with three carbons has eight hydrogen atoms; C3H8. b. A cycloalkane with four carbons has eight hydrogen atoms; C4H8. c. A cycloalkane with nine carbons has 18 hydrogen atoms; C9H18. d. An acyclic alkane with seven carbons has 16 hydrogen atoms; C7H16.

12.2 An acyclic alkane has the molecular formula CnH2n + 2, whereas a cycloalkane has the molecular

formula CnH2n.

a. C5H12, 5 × 2 + 2 = 12: acyclic c. C12H24, 12 × 2 = 24: cyclic b. C4H8, 4 × 2 = 8: cyclic d. C10H22, 10 × 2 + 2 = 22: acyclic

12.3 To determine if the compounds are isomers, first compare molecular formulas as in Example 12.1; two compounds are isomers only if they have the same molecular formula. Then check how the atoms are connected to each other. Constitutional isomers have atoms bonded to different atoms.

a. CH3CH2CH2CH3 and CH3CH2CH3

CH3

b. CH3CH2CH2OH and CH3OCH2CH3

c. andC4H10 C3H8

different molecular formulasnot isomers

C3H8O C3H8Osame molecular formula

different arrangement of atomsisomers

C6H12 C6H12same molecular formula

different arrangement of atomsisomers

12.4 Draw two isomers as in Example 12.2. Since isomers are different compounds with the same molecular formula, add a one-carbon branch to two different carbons to form two different molecules. Then add enough H’s to give each C four bonds.

C C C C

C C C C

C C C C

CAdd H's

Add H'sisomers

CH3CHCHCH3

CH3CCH2CH3

CH3

CH3

CH3

CH3

Add 2 C's to different carbons.C

C

C

��E\�0F*UDZ�+LOO�(GXFDWLRQ��7KLV�LV�SURSULHWDU\�PDWHULDO�VROHO\�IRU�DXWKRUL]HG�LQVWUXFWRU�XVH��1RW�DXWKRUL]HG�IRU�VDOH�RU�GLVWULEXWLRQ�LQ�DQ\�PDQQHU��7KLV�GRFXPHQW�PD\�QRW�EH�FRSLHG��VFDQQHG��GXSOLFDWHG��IRUZDUGHG��GLVWULEXWHG��RU�SRVWHG�RQ�D�ZHEVLWH��LQ�ZKROH�RU�SDUW�

Alkanes 12–2

12.5 Isopentane has 4 C’s in a row with a one-carbon branch.

CH3 CC CH3

CH3 CH3 CC C

CH3

CH3CH2 CCH3

CH3

H

H

HH

HH

HH

HH

CH3CH2CH(CH3)2a. b. c. d.

5 C's in a rownot isopentane

isopentane isopentane

isopentane

12.6 To classify a carbon atom, count the number of C’s bonded to it as in Example 12.3. Draw a complete structure with all bonds and atoms to clarify the structure if necessary.

CH3 CCH3

HCH2CH3a. CH3CH2CH2CH3 b. (CH3)3CH c.

1o

2o

1o 3o1o

2o3o

CH3 CCH3

CH3

CH3d.

1o

1o4o

12.7 Draw a structure to fit each description.

CH3CH2CH3 CH3CCH2CCH3

CH3

CH3

CH3

CH3

CH3CHCH2CH3CH3

a. b. c.

1°

4°C5H12

3° 4°2°

1°

12.8 Draw a skeletal structure for each compound.

a. b.CH3CH2CH2CH2CH2CH3 CH3(CH2)5CH3= = 12.9 Convert each skeletal structure to a complete structure with all atoms and bond lines.

a.

b.

c.C C C C C HH

HH

H

H

H

H

H

H

H

H

C C C C C H

C

H

HH

H

H H

H H

HH

HH

H

CC C

CC

C C C

HH

HH

HH

H HH

H H

H H

HH

H


Chapter 12–3

12.10 To give the IUPAC name for each compound, follow the steps in Example 12.4: [1] Name the parent and use the suffix -ane since the molecule is an alkane. [2] Number the chain to give the first substituent the lower number. [3] Name and number the substituents. [4] Combine the parts.

CH3CH2CHCH2CH3

CH3

a.

5 C's in the longest chain pentane

CH3CH2CHCH2CH3

CH31 2 53

3-methylpentaneCH3CH2CHCH2CH3

CH3

methyl at C3

3

CH3CH2CH2

HCH2CH2CH2CH3C

CH3

CCH2CH2CH3

Hb.

5

methyl at C4

9 C's in the longest chain nonane

CH3CH2CH2

HCH2CH2CH2CH3C

CH3

CCH2CH2CH3

H1 2 4

CH3CH2CH2

HCH2CH2CH2CH3C

CH3

CCH2CH2CH3

H

propyl at C5

4-methyl-5-propylnonane

H CCH2CH3

CH3

CH2 CHCH3

CH3

c.

126 C's in the longest chain

hexane

H CCH2CH3

CH3

CH2 CHCH3

CH34

H CCH2CH3

CH3

CH2 CHCH3

CH324

methyls at C2 and C4

2,4-dimethylhexane

12.11 To give the IUPAC name for each compound follow the steps in Example 12.4.

24

2,3-dimethylbutanea. (CH3)2CHCH(CH3)2 C CCH3

CH3

H HCH3

CH34 C's in the longest chain

butane

C CCH3

CH3

H HCH3

CH31


10 C's in the longest chain decane

4

b. CH3CH2CH2CHCH2C

CH2CH2CH2CH3

H

H

CH3CH2

CH3CH2CH2CHCH2C

CH2CH2CH2CH3

H

H

CH3CH21 2

6

ethyl at C4

4-ethyldecane


Alkanes 12–4

CH3CH2CH2CH2 CCH3

CH2

CCH3

CH2CH3

H

CH3

c.

12

8 C's in the longest chain octane

CH3CH2CH2CH2 CCH3

CH2

CCH3

CH2CH3

H

CH3

4 3

ethyl at C4 methyl at C3

methyl at C4

4-ethyl-3,4-dimethyloctane

12.12 To draw the structure corresponding to each IUPAC name, follow the steps in Example 12.5.

CH3CH2CHCH2CH2CH3

CH3

a. 3-methylhexane

C C C C C C C C C CC

Draw 6 C's and number the chain:

21 3 4 5Add 1 CH3

group 2 3Add H's

C

6

C

CH3CH2CCH2CH3

CH3

CH3

b. 3,3-dimethylpentane



21 3 4 5Add 2 CH3

groups 2 3 Add H's

C

CH3CH2CHCH2CCH2CH2CH3

CH3

CH3

CH3

!c. 3,5,5-trimethyloctane



21 3 4 5Add 3 CH3

groups 2 3Add H's

C

6

CC C C CC

C 57 8

CH3CH2CHCHCH2CH3

CH2

CH3

CH3

!d. 3-ethyl-4-methylhexane



21 3 4 5Add 2 alkyl

groups 2 3Add H's

C

6

C

C

C

4


Chapter 12–5

12.13 To draw the structure corresponding to each IUPAC name, follow the steps in Example 12.5.

a. 2,2-dimethylbutane

CH3CCH2CH3

CH3

CH3

C C C C C C C C


21 3 4Add 2 CH3

groups 2Add H's

C

C

Add 2 alkylgroups

b. 6-butyl-3-methyldecane

CH3CH2CHCH2CH2CHCH2CH2CH2CH3

CH2CH2CH2CH3

CH3



21 3 4 5 3Add H's

C

6

CC C C C

67 8

C C

9 10

C C C CC C

c. 4,4,5,5-tetramethylnonane

CH3CH2CH2C CCH2CH2CH2CH3

CH3

CH3

CH3

CH3

C C C C C C C C C C


21 3 4 5Add 4 CH3

groupsAdd H's

C

6

CC C C

57 8

C

9

C

C

C

C4

C C

d. 3-ethyl-5-propylnonane

CH3CH2CHCH2CHCH2CH2CH2CH3

CH2CH3

CH2CH2CH3

C C C C C C C C C C


21 3 4 5Add 2 alkyl

groupsAdd H's

C

6

CC C C

5

7 8

C

9

CC

C C C3

C C


Alkanes 12–6

12.14 Label the functional groups.

O

O O

alkene

ketone

alkeneester

12.15 Vitamin D3 has many nonpolar C–C and C–H bonds, which makes it water insoluble but fat soluble.

12.16 To give the IUPAC name for each compound, follow the steps in Example 12.6:

[1] Name the ring. [2] Name and number the substituents.

a.

Start numbering here.

1

Answer: methylcyclobutane

4 C's cyclobutane

methyl at C1CH3

b.

CH3CH3


1

Answer: 1,1-dimethylcyclohexane

6 C's cyclohexane

two methyls at C1

c.CH3CH2

CH2CH2CH3

5 C's cyclopentaneAnswer: 1-ethyl-3-propylcyclopentane


1 3propyl at C3

ethyl at C1

d.CH3

CH2CH3

Answer: 1-ethyl-4-methylcyclohexane

6 C's cyclohexane

methyl at C4

4

ethyl at C1


1


Chapter 12–7

12.17 Give the structure corresponding to each IUPAC name.

a. propylcyclopentane

CH2CH2CH3

CH3

CH3

CH3 CH3

CH3

CH3

CH3

CH2CH3

!!d. 4-ethyl-1,2-dimethylcyclohexaneb. 1,2-dimethylcyclobutane

!c. 1,1,2-trimethylcyclopropane

1

2

12

12

4

12.18 The melting points and boiling points of alkanes increase as the number of carbons increases.

a. Highest boiling point, most carbons: decane b. Lowest boiling point, fewest carbons: pentane c. Highest melting point, most carbons: decane d. Lowest melting point, fewest carbons: pentane

12.19 Vaseline is a complex mixture of hydrocarbons, and is nonpolar, so it is insoluble in a polar

solvent like water. In a weakly polar solvent like dichloromethane, it is soluble. 12.20 Elastol is a high molecular weight alkane, making it nonpolar. By the solubility rule, “Like

dissolves like,” nonpolar oil has similar intermolecular forces to nonpolar polyisobutylene, so it is soluble in Elastol.

12.21 Write a balanced equation for each reaction. Combustion reactions release CO2 and H2O.

CH3CH2CH3 + 5 O2

+ 13 O2

a.

b. 2 CH3CH2CH2CH3

3 CO2 + 4 H2O

8 CO2 + 10 H2O

flame

flame

12.22 Write a balanced equation for the reaction. Incomplete combustion reactions release CO and H2O.

2 CH3CH3 + 5 O2 4 CO + 6 H2O Solutions to End-of-Chapter Problems 12.23 Use the formula CnH2n + 2 to determine the number of hydrogen atoms.

(31 × 2) + 2 = 64 H’s 12.24 C18H38 is the molecular formula of an acyclic alkane because it satisfies the 2n + 2 rule;

C18H2(18) + 2.


Alkanes 12–8

12.25 Use the formula CnH2n + 2 to determine the number of hydrogen atoms.

A C26 alkane has 54 H’s [(26 × 2) + 2 = 54]. A C27 alkane has 56 H’s [(27 × 2) + 2 = 56]. A C28 alkane has 58 H’s [(28 × 2) + 2 = 58]. A C29 alkane has 60 H’s [(29 × 2) + 2 = 60]. A C30 alkane has 62 H’s [(30 × 2) + 2 = 62].

12.26 a. A straight-chain alkane has the formula CnH2n + 2. 2n + 2 = 20; n = 9 C’s b. A branched-chain alkane has the formula CnH2n + 2. 2n + 2 = 20; n = 9 C’s c. A cycloalkane has the formula CnH2n. 2n = 20; n = 10 C’s 12.27 To form a cycloalkane, you need to form a C–C bond between 2 C’s in a chain. To do this, 1 H

from each C must be removed. This means a cycloalkane always has two fewer H’s than an acyclic alkane of the same number of C’s.

12.28 A branched-chain alkane contains one or more carbon branches bonded to a carbon chain and has

the general formula CnH2n + 2. A cycloalkane contains carbons joined in one or more rings and has the general formula CnH2n.

12.29 To classify a carbon atom, count the number of C’s bonded to it as in Example 12.3. Draw a

complete structure with all bonds and atoms to clarify the structure if necessary.

CH3(CH2)3CH3 (CH3)3CC(CH3)3

CH3CH2CHCHCH3CH3

CH3 CH3 CH3CH3

a.

b.

c.

d.

1o

2o

1o

1o2o

3o

1o 1o

4o

1o

1o

2o

3o4o

12.30 Draw a structure to satisfy the requirements.

a. b.

4°

2°

CH3CCH3

CH3

CH3

1°

only 2° C's

c.

4°

CH3CCH3

CH2CH3

CH3

d.

3°


Chapter 12–9

12.31 Draw a structure to satisfy the requirements.

CH3CH2CH2CCH3

CH3

CH3a. b. CH3CH2CH2CH2CH2CH2CH3

4° only 1° and 2° C's

1° 1°2°

12.32 Yes, it is possible to have an alkane that contains only 1° carbons. It’s called ethane: CH3CH3. 12.33 To determine if the compounds are isomers, first compare molecular formulas as in Example

12.1; two compounds are isomers only if they have the same molecular formula. Then check how the atoms are connected to each other. Constitutional isomers have atoms bonded to different atoms.

and

andd.CH3

CH3

CH3 CH3

CH3CHCHCH3

CH2CH3

CH2CH3

CH3CH2CHCH2CH(CH3)2

CH3anda.

b.

c.

CH3CHCHCH3

CH2CH3

CH2CH3

andCH3CH2CHCHCH2CH3

CH3

CH3

CH3

CH3CH2CH3

C8H18 C8H18same molecular formulaconstitutional isomers

C5H10 C5H10

same molecular formulaconstitutional isomers


identical connectivityidentical

C8H16 C8H16


12.34 To determine if the compounds are isomers, first compare molecular formulas as in Example

12.1; two compounds are isomers only if they have the same molecular formula. Then check how the atoms are connected to each other. Constitutional isomers have atoms bonded to different atoms.

and

andd.

CH3CH2CH2CH3 CH3CH2CH2CH2CH3 anda.

b.

c.

CH3(CH2)4CH3andCH3CH2

C4H10 C5H12


C5H12 C5H10



identical connectivityidentical

C3H6O2 C3H6O2


H2C CH2

CH2CH3

CH3CH2CH2CH2CH3

CO

OCH3CH3 C

O

OHCH3CH2


Alkanes 12–10

12.35 To determine if the molecules are constitutional isomers or identical, determine if the atoms are connected to each other in the same way.

H CCH3

CH2CH2CH3

CH3

5 C's in a rowCH3 bonded to second C

CH3CHCHCH3

CH3

CH3

CH3CHCH3

CH2CH2CH3

CH3

CH3CHCH2CH2

CH3 CH2CH3

CH3CHCH2CH3a. b. c. d. e.

4 C's in a rowconstitutional isomers

5 C's in a rowidentical

5 C's in a rowCH3 bonded to middle Cconstitutional isomers



12.36 To determine if the molecules are constitutional isomers or identical, determine if the atoms are

connected to each other in the same way.

and

andd.

CH3(CH2)3CHCH3 anda.

b.

c.

and

C7H16 C7H16


C7H16


C7H16

same molecular formulaidentical connectivity

identical

same molecular formulaidentical connectivity

identical

CH3

C7H16

CHCH3

HCH2CH2CH2 C

H

CH3

H

CH3(CH2)3CHCH3

C7H16CH3

CH3CH2CH2CHCH2CH3

CH3

C7H16

CH3CH2CH2CHCH2CH3

CH3

C7H16

CH3CH2CHCH2CH2CH3CH3

e. CH3(CH2)3CHCH3

C7H16CH3

and

C7H16




Chapter 12–11

12.37 Draw structures that fit each description.

CH3

a.

b. CH3CH2CH2CH2CH2OH CH3OCH2CH2CH2CH3

CH2CH3

c. CH3CH2CH2Cl CH3CHCH3

Clcycloalkanes

constitutional isomersC7H14

constitutional isomersC5H12O

etheralcohol

constitutional isomersC3H7Cl

12.38 Draw all of the structures that satisfy the criteria.

CH3CH2CH2CH2CH2CH3 CH3CHCH2CH2CH3 CH3CH2CHCH2CH3

CH3 CH3

CH3CCH2CH3CH3

CH3CH3CHCHCH3

CH3

CH3 12.39 Draw all of the structures that satisfy the criteria.

CH3CHCH2CH2CH2CH2CH3 CH3CH2CHCH2CH2CH2CH3 CH3CH2CH2CHCH2CH2CH3

CH3 CH3 CH3

molecular formula C8H187 C's in the longest chain

one CH3 group bonded to each chain 12.40 Draw all of the structures that satisfy the criteria.

CH3 CH3

CH3

CH2CH3 CH3H3C

12.41 Draw all of the structures that satisfy the criteria.

molecular formula C3H6O: CH3CCH3

O OOH CH3

alcohol ketone cyclic ether


Alkanes 12–12

12.42 Draw one constitutional isomer for each molecule.

a.CO

CH3CH3CH2CO

H CH2CH2CH3

b. CH3CH2CHCH3

NH2CH3CH2CH2CH2NH2

c.

OH

CH2OHone isomer of is

one isomer of is

one isomer of is

12.43 Give the IUPAC name for each molecule.

CH3CH2CH2 C CH3

CH3

HCH3CH2 C CH2CH2

CH3

HCH3CH2 C CH3

CH3

CH3

C C CH3

CH3

HCH3CH2CH2CH2CH2CH3

hexane 2-methylpentane 3-methylpentane 2,2-dimethylbutane 2,3-dimethylbutane

CH3

CH3

H


CH3 CH3

CH3

CH2CH3 CH3H3C

cyclopentane methylcyclobutane 1,2-dimethylcyclopropane ethylcyclopropane 1,1-dimethylcyclopropane 12.45 Give the IUPAC name for each molecule.

CH3CH2CH2 C CH2CH2CH3

CH3

H

7 C's = heptane4-methylheptane

41

C

CC

C

C

CH2CH3

H

HHH

H

HH

H H

5 C's in a ring = cyclopentaneethylcyclopentane

a. b.


Chapter 12–13


3

1

a. CH3CH2CH2CH2 CCH3

HCH2CH3

7 C's = heptane3-methylheptane

b.C CC C

HH H

H

H

CH3CH3

H

4 C's in a ring = cyclobutane1,2-dimethylcyclobutane

1 2

12.47 To give the IUPAC name for each compound, follow the steps in Example 12.4.


CH3

CH3CH2CHCH2CHCH2CH2CH3

CH3 CH3

CH3CH2CH2C(CH2CH3)3

CH3CHCH2C HCH2CH3

CH2CH3

CH2CHCH3

CH3

a.

b.

c.

d.

(CH3CH2)2CHCH2CH2CH2CH(CH3)2

CH3CH2 CCH3

CH3

CH2CH2

CH2CH2CH2 CCH3

CH3

CH3

e.

f.

2,2,8,8-tetramethyldecane

7 C's = heptane

31

methyl at C3

3-methylheptane

31 5


8 C's = octane3,5-dimethyloctane

CH3CH2CH2CCH2CH3

CH2CH3

CH2CH3

6 C's = hexane3,3-diethylhexane

3 1

two ethyls at C3

12

4

6methyls at C2 and C6

ethyl at C4

4-ethyl-2,6-dimethyloctane8 C's = octane

CCH2CH2CH2CCH3CH3CH2

CH3CH2

H CH3

H

8 C's = octane6-ethyl-2-methyloctane

1

methyl at C2

ethyl at C6 2

10 C's = decane

two methyls at C2two methyls at C8

12

8


Alkanes 12–14


a.

b.

c.

d.

e.

5 C's = pentane

2

1

2,3-dimethylpentane

6 C's = hexane3,3-dimethylhexane

CH

CH2CH3

CHCH3CH3

CH3

CH3CH2 CCH3

CH3

CH2CH2CH3

13 2 methyls at C3

9 C's = nonane5-ethylnonane

CH3CH2 CHCH2CH2CH2CH3

CH2CH2CH2CH3

15

ethyl at C5

(CH3CH2)2CHCH(CH2CH3)2

CH

CHCH2CH3CH3CH2CH2CH3

CH3CH21

3

4

6 C's = hexane3,4-diethylhexane

2 ethyls at C3 and C4

6 C's = hexane

1

4-ethyl-2,2-dimethylhexane

CCH3

CH3

CH2CH3 CH

CH2CH3

CH2CH3

ethyl at C4

2 methyls at C224

f.

8 C's = octane

1

5-ethyl-2,6-dimethyloctane

CH

CH3

CH2CH2CH3 Cethyl at C5CH2CH3

HCHCH2CH3

CH32 5 62 methyls at C2 and C6

3

5methyl at C3

methyl at C2


a.

b.

c.

d.CH3

CH3CH3

CH3CH3

CH3CH2 CH2CH3

6 C's = cyclohexane1,3-diethylcyclohexane

8 C's = cyclooctane

3 C's = cyclopropanemethylcyclopropane

methyl

4 C's = cyclobutane1,1,2,2-tetramethylcyclobutane

1

2

1 3


Chapter 12–15


a.

b.

c.

d.

6 C's = cyclohexane4-butyl-2-ethyl-1-methylcyclohexane

7 C's = cycloheptane

6 C's = cyclohexane1-butyl-2-propylcyclohexane

propyl

CH2CH3 ethyl

ethylcycloheptane

CH2CH2CH3

CH2CH2CH2CH3

1

2

butyl

CH2CH2CH3

CH2CH3

1propyl

ethyl

5 C's = cyclopentane1-ethyl-1-propylcyclopentane

CH2CH2CH2CH3

CH3CH2

CH3

1 4

2 butylethyl

methyl


a. 3-ethylhexane

CH3CH2CHCH2CH2CH3

CH2CH3

b. 3-ethyl-3-methyloctane

CH3CH2CCH2CH2CH2CH2CH3

CH3

CH2CH3

ethyl at C3

methyl at C3

ethyl at C3

CH3CHCHCHCHCH2CH2CH2CH2CH3

c. 2,3,4,5-tetramethyldecane

CH3 CH3

CH3 CH3

d. cyclononane

e. 1,1,3-trimethylcyclohexaneCH3 CH3

CH3

f. 1-ethyl-2,3-dimethylcyclopentane

CH2CH3

CH3

CH3

four methyl groups at C2, C3, C4, and C5

three methyl groups

ethyl at C1

two methyl groups

1 2

3

12

3


a. 3-ethyl-3-methylhexane

CH3CH2CCH2CH2CH3

CH2CH3

d. 1,3,5-triethylcycloheptane

ethyl at C3

CH3 methyl at C3 CH2CH3

CH2CH3

H3CH2C three ethyls at C1, C3, C5


Alkanes 12–16

e. 3-ethyl-3,4-dimethylnonane

CH3CH2C

b. 2,2,3,4-tetramethylhexane

CH3C4 methyls at C2, C3 and C4

CH3

CH3

CH CHCH2CH3

CH3 CH3 CH2CH3

CH3

CHCH2CH2CH2CH2CH3

CH3

ethyl at C3

2 methyls at C3, C4

f. 2-ethyl-1-methyl-3-propylcyclopentanec. 4-ethyl-2,2-dimethyloctane

CH3CCH3

CH3

CH2CHCH2CH2CH2CH3

CH2CH3 ethyl at C4

2 methyls at C2 CH3

CH2CH3

CH2CH2CH3

methyl at C1

ethyl at C2

ethyl at C4 12.53 Explain why each IUPAC name is incorrect. a. 2-methylbutane: Number to give CH3 the

lower number, 2 not 3.

CH3CHCH2CH3CH3

C2

d. 2,5-dimethylheptane: longest chain not chosen

CH3CHCH2CH2CHCH2CH3CH3 CH3

b. methylcyclopentane: no number assigned if only one substituent

CH3

e. 1,3-dimethylcyclohexane: Number to give the second substituent the lower number.

CH3

CH3

C1

C3

c. 2-methylpentane: five-carbon chain

CH3CHCH2CH2CH3CH3

f. 1-ethyl-2-propylcyclopentane: lower number assigned alphabetically

CH2CH3C1

CH2CH2CH3C2

12.54 Explain why each IUPAC name is incorrect. a. 2-methylpentane: Number to give CH3 the

lower number (i.e., 2 not 4).

CH3CHCH2CH2CH3CH3

C2

d. 3,5-dimethylheptane: longest chain not chosen

CH3CH2CHCH2CHCH2CH3

CH3 CH3


Chapter 12–17

b. 2,2,3-trimethylbutane: Number to give lower numbers to CH3 groups.

CH3CCH3

CH3

CHCH3

CH3

e. 1-ethyl-1-methylcycloheptane: number ring starting with substituents

CH3

CH2CH3

c. 3-methylhexane: six-carbon chain


f. 1,2-diethylcyclohexane: number to give substituents lowest numbers

CH2CH3

CH2CH3

C2 not C6

12.55 Draw the isomers and then give the IUPAC name.

CH3

CH3

CH3

CH3

CH3CH3

1,2-dimethylcyclopentane 1,3-dimethylcyclopentane 1,1-dimethylcyclopentane 12.56 Draw the isomers and then give the IUPAC name.

ethylcyclobutane 1,2-dimethylcyclobutane

CH3CH3

1,1-dimethylcyclobutane

CH2CH3CH3

CH31,3-dimethylcyclobutane

CH3

H3C

12.57 Draw a skeletal structure for each compound.

CH3CHCH2CH2CH2CH2CH3

CH3

a. octane b. 1,2-dimethylcyclopentane c.CH3

CH3 12.58 Draw a skeletal structure for each compound.

a. CH3(CH2)7CH3 b. 1,1-diethylcyclohexane c. (CH3CH2)2CHCH2CH2CH3


Alkanes 12–18

12.59 Convert each structure to a complete structure with all atoms drawn in.

C C C C C C C C C HCH

HH

H

H H

H H

H H

H H

H H

H

H

H

H

H H

HC C C C HC

H

HH

C

H H

H

H H

H

CHHHH

H

C CCC

C CH H

H

H

H

H

HHH

HH

H

H

a. b. c.

12.60 Convert each structure into a complete structure with all atoms drawn in.

a. b. c.

CH

HH

CH

HCH

HC

C

HCH

HCH

CH

HC

H

H

HCH

HH

HH

H

C C

CC

C

H H

HH

HH

HH

HCH

HCH

HCH

HCH

HH

CH

HH

CH

HCH

C

CH

CH

C

CH

HH

H

H HH

H HH


a. or

more carbon atomshigher melting point

b. or

more carbon atomshigher melting point


cyclobutane or cyclopentanea. b.more carbon atoms

higher boiling pointmore carbon atoms

higher boiling point

cyclopentane or ethylcyclopentane


Chapter 12–19

12.63 Branched alkanes have lower boiling points than linear alkanes.

a. increasing boiling point: (CH3)4C < (CH3)2CHCH2CH3 < CH3CH2CH2CH2CH3

b. increasing boiling point: (CH3)2CHCH(CH3)2 < CH3CH2CH2CH(CH3)2 < CH3(CH2)4CH3

most branching no branching

most branching no branching 12.64 The boiling points of heptane and H2O are similar, even though heptane has a much higher

molecular weight and greater surface area, because H2O can form intermolecular hydrogen bonds, thus giving water a much higher boiling point than would otherwise be expected of such a low molecular weight compound. Heptane is a nonpolar molecule and cannot form hydrogen bonds.

12.65 Hexane is a nonpolar hydrocarbon, making it soluble in organic solvents like dichloromethane,

but insoluble in water. 12.66 Vaseline, a solid, contains a larger number of carbon atoms than mineral oil, a liquid. The melting

point increases with increasing number of carbon atoms. 12.67 Write a balanced equation for each reaction. Combustion reactions form CO2 and H2O.

a. b.2 CH3CH3 + 7 O2 4 CO2 + 6 H2O (CH3)2CHCH2CH3 + 8 O2 5 CO2 + 6 H2O

12.68 Write a balanced equation for each reaction. Combustion reactions form CO2 and H2O.

a. b. + 9 O2 6 CO2 + 6 H2O + 15 O2 10 CO2 + 10 H2O2

12.69 Write a balanced equation for each reaction. Incomplete combustion reactions form CO and H2O.

a. b.2 CH3CH2CH3 + 7 O2 6 CO + 8 H2O 2 CH3CH2CH2CH3 + 9 O2 8 CO + 10 H2O 12.70 Write a balanced equation for the reaction. Incomplete combustion reactions form CO and H2O.

2 C6H6 + 9 O2 12 CO + 6 H2O 12.71 Write a balanced equation for the oxidation of glucose to form CO2 and H2O.

C6H12O6 + 6 O2 6 CO2 + 6 H2O 12.72 Write a balanced equation for the combustion of ethanol to form CO2 and H2O.

CH3CH2OH + 3 O2 2 CO2 + 3 H2O 12.73 Higher molecular weight alkanes in warmer weather means less evaporation. Lower molecular

weight alkanes in colder weather means the gasoline won’t freeze.


Alkanes 12–20

12.74 The concrete foundation of a new house is often wrapped in polyethylene, a high molecular weight alkane, to prevent water from seeping into the house. The nonpolar alkane will not allow the polar water molecules to pass through.

12.75 The mineral oil can prevent the body’s absorption of important fat-soluble vitamins. The vitamins

dissolve in the mineral oil, and are thus not absorbed. Instead, they are expelled with the mineral oil.

12.76 A fire in a fireplace in a poorly ventilated room poses a health hazard, because incomplete

combustion forms carbon monoxide, a toxic gas. The concentration of CO can reach an unhealthy level if the room does not allow proper ventilation.

12.77 c. The nonpolar asphalt will be most soluble in the paint thinner because “like dissolves like.”

The liquid alkanes of the paint thinner dissolve the high molecular weight hydrocarbons of the asphalt.

12.78

CO

O (CH2)16CH3H2C

C CO

O (CH2)16CH3H

CO

O (CH2)16CH3H2C

a.

3 ester groups

CO

O (CH2)16CH3H2C

C CO

O (CH2)16CH3H

CO

O (CH2)16CH3H2C

!+ !" !"!+

!+!"

!+ !"

!"

!"!+

!+

b.

c. Tristearin will dissolve in an organic solvent like hexane because it is also an organic molecule and “like dissolves like.” Tristearin does not dissolve in water because the nonpolar chains on the molecule are too large, making the compound insoluble in water even though the ester portion of the molecule is polar.

12.79 Answer each question about the compound.

CH3CH2CH2 CCH3

CH3

CCH2CH3

HCH2CH3a.

CH3CH2CH CCH3

HCCH2CH3

HCH2CH3

CH3

c. not water solubled. soluble in organic solvents

C11H24 + 17 O2 11 CO2 + 12 H2Oe.

f.

7 C's = heptane3-ethyl-4,4-dimethylheptane

b.

constitutional isomer


Chapter 12–21

12.80 Answer each question about the compound.

CH3CH2CH2 CH

CCH2CH3

CH3

CH2CH3a.

CH3CH2CH2 CCH3

HCCH2CH3

CH2CH3

CH2CH3


2 C12H26 + 37 O2 24 CO2 + 26 H2Oe.

f.

7 C's = heptane3,4-diethyl-3-methylheptane

b.

constitutional isomer

CH3CH2

12.81


C8H16 + 12 O2 8 CO2 + 8 H2Oe.

f.constitutional isomer

a.

5 C's in a ring = cyclopentanepropylcyclopentane

b. CH3

CH3CH2

12.82


C8H16 + 12 O2 8 CO2 + 8 H2Oe.

f.constitutional isomer

a.

4 C's in a ring = cyclobutane1,1-diethylcyclobutane

b.CH2CH3

CH2CH3

CH2CH3

CH2CH3

12.83 A compound with 10 carbons and two rings will have 2n – 2 H’s.

(10 × 2) – 2 = 18 C10H18

12.84 Draw the 12 constitutional isomers of C6H12 that contain one ring.

12.85 Cyclopentane has a more rigid structure. The rings can get closer together since they are not

floppy, resulting in an increased force of attraction. Therefore, the boiling point is higher.


Alkanes 12–22

12.86 Draw the structures of the seven constitutional isomers of C4H10O.

OH

OHO

OOH

OH O


Documents

Chapter 12 Alkanes - websites.rcc.eduwebsites.rcc.edu/grey/files/2012/02/Chapter-12-Solutions-Smith.pdf · Chapter 12–1 Chapter 12 Alkanes Solutions to In -Chapter Problems 12.1