CHEMISTRY 122
CHAPTER #2 ALKANES
Sp 2013
14,18 ,19,20,22, 23, 26, 27, 32, 35, 36, 40, 46, 48, 59, 60, 62,
2-14
Line-angle formulas are:
(a)
(d)
(b)
(e)
(c)
(f)
2-18
Structures (a) and (g) represent the same compound. So do structures (d) and (e).
Structures (a, g), (d, e), and (f) represent constitutional isomers with molecular
formula C4H10O. Structures (b) and (c) represent constitutional isomers with
molecular formula C4H8O
2-19
See Appendix A11
2-20
None represent the same compound. There are three sets of constitutional
isomers. Compounds (a), (d), and (e) with the molecular formula C4H8O are one
set. Compounds (c) and (f) with the molecular formula C5H10O are a second set,
and compounds (g) and (h) with the molecular formula C6H10O are a third set.
2-22
The nine constitutional isomers with the molecular formula C7H16 are:
2-23
See Appendix A11
2-26
(a)
True
(b) False: the octane rating compares the antiknock properties of a test gasoline
to that of a reference mixture of 2,2,4-trimethylpentane and heptane, where
100% 2,2,4-trimethylpentane has an octane rating of 100 and 100% heptane
has an octane rating of 0.
(c) False: they are constitutional isomers, but 2,2,4-trimethylpentane has an
octane rating of 100 and octane has an octane rating of –20.
2-27
See Appendix A11
2-32
H
H
H
H
H
H
Staggard (most stable)
H H
H
H
H
H
Eclipsed (least stable)
2-35
See Appendix A11
2-36
No. Cis-trans isomerism results when there is restricted rotation about carboncarbon bonds. Alkanes have free rotation about their carbon-carbon bonds.
2-40
(a)
The six-membered rings are in the chair conformation. The five-membered ring
is nearly planar, approximating an envelope structure.
(b) The hydroxyl on ring A is in the equatorial position.
(c) The methyl group between rings A and B is in the axial position.
2-46
Alkanes are nonpolar and insoluble in very polar water.
2-48
Boiling points of unbranched alkanes are related to their surface area, the larger
the surface area, the greater the strength of dispersion forces, and the higher the
boiling point. The relative increase in size per CH2 group is greatest between CH4
and CH3CH3 and becomes progressively smaller as the molecular weight
increases. Therefore, the increase in boiling point per added CH2 group is greatest
between CH4 and CH3CH3, and becomes progressively smaller for higher alkanes.
2-59
See Appendix A11
2-60
An octane rating indicates the relative smoothness with which a gasoline blend
burns in an automobile engine. The higher the octane rating, the less the engine
knocks. The reference hydrocarbons are 2,2,4-trimethylpentane (isooctane),
which is assigned an octane rating of 100, and heptane, which is assigned an
octane rating of 0.
2-62
2,2,4-Trimethylpentane has a higher heat of combustion both per mole and per
gram.
2-65
Molar mass
(g/mol)
2,2,4-Trimethylpentane
Ethanol
114.2
46.0
Heat of Combustion
kcal/mol
kcal/g
1304
327
11.4
7.11