Chemistry - A Molecular Science

Chapter 13 Organic Chemistry

Alkenes and alkynes are named in a similar manner, but with the additional
requirement that the position of the multiple bond(s) must be established. The procedure for naming simple alkenes and alkynes is summarized in the margin. Example 13.2

Name the following organic molecules:

(a) (b) (c) (e)

(d)

a) The continuous chains of this branched alkane are highlighted with thick lines in the

margin. The continuous chains in (a) and

(b) contain only four carbons, while the

longest continuous chain (c) contains five

carbons. Because the longest continuous

chain contains five carbon atoms, the

compound is named as a pentane. We next

identify the type and position of the attach

ed group. The attached group contains only

one carbon atom and is, therefore, a methyl group. (d) and (e) show that the methyl group is located on the third carbon, regardl

ess of the end at which the numbering is

started. The name of

the compound is therefore 3-methylpentane.

b) This is also a branched alkane. The contin

uous chains are shown in the margin with

thick lines. (f) is a six-carbon chain; (g) is a seven-carbon chain; and (h) is an eight-carbon chain. The longest chain contains eight carbons, so this compound is named an octane. The branch contains two carbon at

oms and is therefore an ethyl group. The

ethyl group is located on the fourth carbon if

the numbering is as in (i), but it is attached

to the fifth carbon if numbering is as in (j).

The compound is named so that the branch is

at the lower number. Consequently, th

is compound is 4-ethyloctane.

c) This molecule is a branched alkane with

two branches. The continuous chains are

shown as thick lines in the margin. The chains in (k), (n) and (o) each contain five atoms, while (l) and (m) are each six-carbon

chains. This branch

ed chain alkane is,

therefore, named as a hexan

e, 3-ethyl-4-methylhexane.

d) This is an alkene containing a six-carb

on chain, so it is a hexene. The chain is

numbered starting at the end closest to the doub

le bond, so it is a 2-hexene. As we will

see in Example 13.5 of the next section, th

ere are actually two different compounds that

are 2-hexene. The complete name that id

entifies the 2-hexene is given there.

e) The triple bond comes after the second carbon in a four-carbon chain, so this compound

is 2-butyne.

(a)

(b)

(c)

4 3

5

2

1

2 3

1

4

5

(d)

(e)

4

3

2

1

5

6 7

8

5

6

7

8

4

3 2

1

(i)

(j)

(f)

(g)

(h)

(l)

(m)

(n)

(o)

(k)

Example 13.2

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