Organic Chemistry

64 CHAPTER 2 An Introduction to Organic Compounds

If a hydrogen of an alkane is replaced by an OH, the compound becomes an

alcohol; if it is replaced by an the compound becomes an amine; and if it is re-

placed by a halogen, the compound becomes an alkyl halide.

An alkyl group name followed by the name of the class of the compound (alcohol,

amine, etc.) yields the common name of the compound. The following examples show

how alkyl group names are used to build common names:

Notice that there is a space between the name of the alkyl group and the name of the

class of compound, except in the case of amines.

Two alkyl groups—a propyl group and an isopropyl group—contain three carbon

atoms. A propyl group is obtained when a hydrogen is removed from a primary carbon

of propane. A primary carbonis a carbon that is bonded to only one other carbon. An

isopropyl group is obtained when a hydrogen is removed from the secondary carbon

of propane. A secondary carbonis a carbon that is bonded to two other carbons. No-

tice that an isopropyl group, as its name indicates, has its three carbon atoms arranged

as an iso structural unit.

Molecular structures can be drawn in different ways. Isopropyl chloride, for exam-

ple, is drawn here in two ways. Both represent the same compound. At first glance, the

two-dimensional representations appear to be different: The methyl groups are across

from one another in one structure and at right angles in the other. The structures are

identical, however, because carbon is tetrahedral. The four groups bonded to the cen-

tral carbon—a hydrogen, a chlorine, and two methyl groups—point to the corners of a

tetrahedron. If you rotate the three-dimensional model on the right 90°in a clockwise

direction, you should be able to see that the two models are the same. (You can simu-

late this rotation on the Web site http://www.prenhall.com/bruice by visiting the Molecule

Gallery in Chapter 2.)

CH 3 CHCH 3

Cl

CH 3 CHCl

CH 3

isopropyl chloride isopropyl chloride

two different ways to draw isopropyl chloride

CH 3 CH 2 CH 2

a propyl group

CH 3 CHCH 3

an isopropyl group

a primary carbon a secondary carbon

CH 3 CH 2 CH 2 Cl

propyl chloride

CH 3 CHCH 3

isopropyl chloride

Cl

CH 3 OH

methyl alcohol

CH 3 CH 2 NH 2

ethylamine

CH 3 CH 2 CH 2 Br

propyl bromide

CH 3 CH 2 CH 2 CH 2 Cl

butyl chloride

CH 3 I

methyl iodide

CH 3 CH 2 OH

ethyl alcohol

CH 3 CH 2 CH 2 NH 2

propylamine

CH 3 CH 2 CH 2 CH 2 OH

butyl alcohol

ROH

an alcohol

RNH 2

an amine

RX X = F, Cl, Br, or I

an alkyl halide

NH 2 ,

Build models of the two representations

of isopropyl chloride, and convince

yourself that they represent the same

compound.

methyl alcohol

methyl chloride

methylamine

3-D Molecules:

Isopropyl chloride

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