Organic Chemistry

454 CHAPTER 12 Reactions of Alcohols, Ethers, Epoxides, and Sulfur-Containing Compounds

PROBLEM 15 SOLVED

Give the major products that would be obtained from heating each of the following ethers

with HI:

SOLUTION TO 15a The reaction takes place by an pathway because neither alkyl

group will form a relatively stable carbocation. Iodide ion attacks the carbon of the ethyl

group because the other possibility is to attack an hybridized carbon, and carbons

are generally not attacked by nucleophiles (Section 10.8). Thus, the products are ethyl

iodide and an enol that immediately rearranges to an aldehyde (Section 6.6).

12.7 Reactions of Epoxides

Ethers in which the oxygen atom is incorporated into a three-membered ring are called

epoxidesor oxiranes. The common name of an epoxide uses the common name of the

alkene, followed by “oxide,”assuming that the oxygen atom is where the bond of an

alkene would be. The simplest epoxide is ethylene oxide.

There are two systematic ways to name epoxides. One method calls the three-

membered oxygen-containing ring “oxirane,”with oxygen occupying the 1-position

of the ring. Thus, 2-ethyloxirane has an ethyl substituent at the 2-position of the

oxirane ring. Alternatively, an epoxide can be named as an alkane, with an “epoxy”

prefix that identifies the carbons to which the oxygen is attached.

PROBLEM 16

Draw the structure of the following compounds:

a. 2-propyloxirane c. 2,2,3,3-tetramethyloxirane

b. cyclohexene oxide d. 2,3-epoxy-2-methylpentane

2-ethyloxirane

1,2-epoxybutane

H 2 C CHCH 2 CH 3

2,3-dimethyloxirane

2,3-epoxybutane

CH 3 CH CHCH 3

2,2-dimethyloxirane

1,2-epoxy-2-methylpropane

H 2 C

CH 3

CH 3

C

OOO

ethylene

H 2 CCH 2

ethylene oxide

H 2 CCH 2

propylene

H 2 C CHCH 3

propylene oxide

H 2 C

O

CHCH 3

O

p

sp^2 sp^2

SN 2

CHOCH 2 CH 3

CH 3 CH 2 CH 2 OCH 2

CH 3 CH

CH 2 O

OCH 3

CH 3

CH 3

O

O

a.

b.

c.

d.

e.

f.

I

HI

H

− + CH 3 CH 2 I

+

CH 3 CH CH OCH 2 CH 3

O

CH 3 CH CH OCH 2 CH 3 CH 3 CH CH OH CH 3 CH 2 CH

∆

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