Download CHEM 122: Introduction to Organic Chemistry Chapter 2: Alkanes. 1

CHEM 122: Introduction to Organic Chemistry
Chapter 2: Alkanes.
1. For each condensed structural formula, write a line-angle formula.
CH2CH3
CH3
CH3
a) CH3CH2CHCHCH2CHCH3
b) CH3CCH3
CH(CH3)2
c) (CH3)2CHCH(CH3)2
CH3
CH2CH3
d) CH3CH2CCH2CH3
e) (CH3)3CH
f) CH3(CH2)3CH(CH3)2
CH2CH3
2. Write the molecular formula for each alkane
a)
b)
c)
3. Each member of the following set of compounds is an alcohol; that is, each
contains an –OH (hydroxyl group). Which structural formulas represent the same
compound, and which represent constitutional isomers?
OH
OH
OH
a)
b)
c)
OH
HO
d)
OH
e)
f)
OH
OH
g)
h)
4. Each member of the following set of compounds is either an aldehyde or a ketone.
Which structural formulas represent the same compound, and which represent
constitutional isomers?
O
O
O
a)
b)
H
O
c)
O
O
H
d)
e)
f)
O
O
H
g)
h)
5. Draw line-angle formulas for the nine constitutional isomers with the molecular
formula C7H16.
6. Write the IUPAC names for these alkanes and cycloalkanes.
CH3CHCH2CH2CH3
CH3CHCH2CH2CHCH3
CH3(CH2)4CHCH2CH3
a)
b)
c)
CH3
d)
CH3
e)
CH3
f)
7. Write line-angle formulas for these alkanes and cycloalkanes.
a)
b)
c)
d)
e)
f)
g)
h)
2,2,4-Trimethylhexane
2,2-Dimethylpropane
3-Ethyl-2,4,5-trimethyloctane
5-Butyl-2,2-dimethylnonane
4-Isopropyloctane
3,3-Dimethylpentane
trans-1,3-Dimethylcyclopentane
cis-1,2-Diethylcyclobutane
CH2CH3
8. Draw a conformation of ethane in which hydrogen atoms on adjacent carbons are
as far apart as possible. Also draw a conformation in which they are as close
together as possible. In a sample of ethane molecules at room temperature, which
conformation is the more likely?
9. Name and draw structural formulas for the cis and trans isomers of 1,2dimethylcyclopropane.
10. Name and draw structural formulas for the six cycloalkanes with the molecular
formula C5H10. Include cis-trans isomers as well as constitutional isomers.
11. Draw structural formulas for these haloalkanes.
a)
b)
c)
d)
e)
Bromomethane
Chlorocyclohexane
1,2-Dibromoethane
2-Chloro-2-methylpropane
Dichlorodifluoromethane (Freon-12)
12. Tell whether the compounds in each set are constitutional isomers.
a) CH3CH2OH and CH3OCH3
b)
O
O
and
CH3CCH3
c)
CH3CH2CH
O
O
and
CH3COCH3
d)
CH3CH2COH
OH
O
and
CH3CHCH2CH3
e)
f)
CH3CCH2CH3
and
and
CH3CH2CH2CH2CH2CH3
CH2=CHCH2CH2CH2CH3
13. Explain why each of the following is an incorrect IUPAC name. Write the correct
IUPAC name for the compound
a)
b)
c)
d)
e)
f)
g)
h)
1,3-Dimethylbutane
4-Methylpentane
2,2-Diethylbutane
2-Ethyl-3-methylpentane
2-Propylpentane
2,2-Diethylheptane
2,2-Dimethylcyclopropane
1-Ethyl-5-methylcyclohexane
14. Which of the following compounds can exist as cis-trans isomers? For each that
can, draw both isomers using solid and dashed wedges to show the orientation in
space of the –OH and –CH3 groups.
OH
OH
HO
CH 3
CH 3
a)
b)
c)
15. Which unbranched alkane (Table 2.4) has about the same boiling point as water?
Calculate the molecular weight of this alkane, and compare it with the molecular
weight of water. Explain the difference—how similar boiling points are possible
in spite of differences in molecular weight.
16. Suppose that you have samples of hexane and octane. Could you tell the
difference by looking at them? What color would each be? How could you tell
which is which?
17. Write balanced equations for the combustion of each of the following
hydrocarbons. Assume that each is converted completely to carbon dioxide and
water.
a) Hexane
b) Cyclohexane
c) 2-Methylpentane
18. The reaction of chlorine with pentane gives a mixture of three chloroalkanes, each
with the molecular formula C5H11Cl. Write a line-angle formula and the IUPAC
name for each chloroalkane.
19. There are three constitutional isomers with the molecular formula C 5H12. When
heated with chlorine at 300oC, isomer A gives a mixture of four monochlorination
products. Under the same experimental conditions, isomer B gives a mixture of
three monochlorination products and isomer C gives only one monochlorination
product. From this information, deduce the structural formulas, of isomers A, B,
and C.
20. Dodecane, C12H30, is an unbranched alkane. Predict the following:
a)
b)
c)
d)
e)
Will it dissolve in water?
Will it dissolve in hexane?
Will it burn when ignited?
Is it a liquid, solid, or gas at room temperature and atmospheric pressure?
Is it more or less dense than water?
21. Following is a structural formula for 2-isopropyl-5-methylcyclohexanol:
OH
Using a planar hexagon representation for the cyclohexane ring, draw a structural
formula for the cis-trans isomer with isopropyl trans to –OH and methyl cis to –
OH. If you answered this part correctly, you have drawn the isomer found in
nature and given the name menthol.
22. On the left is a representation for 2-deoxy-D-ribose. This molecule is the “D” of
DNA. Convert this representation to the alternative representation using the ring
on the right. (We discuss the structure and chemistry of this compound in more
detail in Chapter 12.)
O
HO
HO
OH
HO
O