The Foundations of Chemistry

The IUPAC naming system is based on the names of the unbranched hydrocarbons
given in Table 27-2 and their higher homologues. To name a branched-chain hydrocarbon,
we first find the longest chain of carbon atoms and use the root name that corresponds
to that hydrocarbon. We then indicate the positions and kinds of substituentsattached to
the chain. Alkyl groupsubstituents attached to the longest chain are thought of as frag-
ments of hydrocarbon molecules obtained by the removal of one hydrogen atom. We give
them names related to the parent hydrocarbons from which they are derived. Other alkyl
groups are named similarly (Table 27-5). We use the general symbol R to represent any
alkyl group. The cycloalkyl groups derived from the first four cycloalkanes are called cyclo-
propyl, cyclobutyl, cyclopentyl, and cyclohexyl, respectively.

cyclopropyl cyclobutyl cyclopentyl cyclohexyl

27-2 Naming Saturated Hydrocarbons 1049

TABLE 27-5 Some Alkanes and the Related Alkyl Groups

Parent Hydrocarbon Alkyl group, —R

CH 4 , methane XCH 3 , methyl

C 2 H 6 , ethane XC 2 H 5 , ethyl

C 3 H 8 , propane XC 3 H 7 , propyl XC 3 H 7 , isopropyl

C 4 H 10 , butane XC 4 H 9 , butyl XC 4 H 9 , sec-butyl

(read as “secondary butyl”)

C 4 H 10 , methylpropane XC 4 H 9 , t-butyl XC 4 H 9 , isobutyl

(common name, isobutane) (read as “tertiary butyl”)

CH 2

CH 3

H C CH 3

CH 3

CH 3

H C CH 3 or C(CH 3 ) 3

CH 3

CH 3

C CH 3 or CH(CH 3 ) 3

HH

HH

C C

H

H C

H

H

C H

HH

HH

C C

H

H

C

H

H

C HCHor 2 (CH 2 ) 2 CH 3

HH

HH

C C

H

H

H C

H

H

C HCHor 3 (CH 2 ) 2 CH 3

HH

H

H C C

H

H

C H

HH

HH

C C

H

H

C HCHor 2 CH 2 CH 3

HH

HH

H C C

H

H

C HCHor 3 CH 2 CH 3

HH

HH

H C C HCHor 2 CH 3

HH

HH

C C HCHor 3 CH 3

H

H

H C H or CH 3

H

H

CCHH or 4