Organic Chemistry

66 CHAPTER 2 An Introduction to Organic Compounds

The prefix “tert”is found in tert-butyl and tert-pentyl because each of these sub-

stituent names describes only one alkyl group. The name “tert-hexyl”cannot be used

because it describes two different alkyl groups. (In older literature, you might find

“amyl”used instead of “pentyl”to designate a five-carbon alkyl group.)

If you examine the following structures, you will see that whenever the prefix “iso”

is used, the iso structural unit will be at one end of the molecule and any group replac-

ing a hydrogen will be at the other end:

Notice that an iso group has a methyl group on the next-to-the-last carbon in the chain.

Notice also that allisoalkyl compounds have the substituent (OH, Cl, etc.) on a

primary carbon, except for isopropyl, which has the substituent on a secondary carbon.

The isopropyl group could have been called a sec-propyl group. Either name would

have been appropriate because the group has an iso structural unit and a hydrogen has

been removed from a secondary carbon. Chemists decided to call it isopropyl, howev-

er, which means that “sec”is used only for sec-butyl.

Alkyl group names are used so frequently that you should learn them. Some of the

most common alkyl group names are compiled in Table 2.2 for your convenience.

PROBLEM 1

Draw the structures and name the four constitutional isomers with molecular formula

C 4 H 9 Br.

NH 2 ,

CH 3 CHCH 2 CH 2 CH 2 Cl

CH 3

isohexyl chloride

CH 3 CHCH 2 CH 2 OH

CH 3

isopentyl alcohol

or

isoamyl alcohol

CH 3 CHCH 2 Br

CH 3

isobutyl bromide

CH 3 CHCH 2 NH 2

CH 3

isobutylamine

CH 3 CHBr

CH 3

isopropyl bromide

CH 3 CHCH 2 CH 2 OH

CH 3

isopentyl alcohol

CH 3 CBr

CH 3

CH 3

tert-butyl bromide

CH 3 C Br

CH 2 CH 3

CH 3

tert-pentyl bromide

CH 3 CH 2 CBr

CH 3

CH 2 CH 3

Both alkyl bromides have six carbon atoms with a

bromine attached to a tertiary carbon, so both

compounds would be named tert-hexyl bromide.

CH 3 CH 2 CH 2 CBr

CH 3

CH 3

Table 2.2 Names of Some Alkyl Groups

CH 3 C

CH 3

CH 3

pentyl CH 3 CH 2 CH 2 CH 2 CH 2

isopentyl CH 3 CHCH 2 CH 2

CH 3

CH 3

sec-butyl CH 3 CH 2 CH

tert-butyl

CH 3

CH 3

methyl

ethyl CH 3 CH 2

propyl CH 3 CH 2 CH 2

isopropyl CH 3 CH

CH 3

isobutyl CH 3 CHCH 2

butyl CH 3 CH 2 CH 2 CH 2

CH 3 CCH 2

CH 3

CH 3

hexyl CH 3 CH 2 CH 2 CH 2 CH 2 CH 2

neopentyl

isohexyl CH 3 CHCH 2 CH 2 CH 2

CH 3

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