Organic Chemistry

2.4 Nomenclature of Alkyl Halides

Alkyl halides are compounds in which a hydrogen of an alkane has been replaced by a

halogen. Alkyl halides are classified as primary, secondary, or tertiary, depending on

the carbon to which the halogen is attached. Primary alkyl halideshave a halogen

bonded to a primary carbon,secondary alkyl halideshave a halogen bonded to a sec-

ondary carbon, and tertiary alkyl halideshave a halogen bonded to a tertiary carbon

(Section 2.1). The lone-pair electrons on the halogens are generally not shown unless

they are needed to draw your attention to some chemical property of the atom.

The common names of alkyl halides consist of the name of the alkyl group, fol-

lowed by the name of the halogen—with the “ine”ending of the halogen name re-

placed by “ide”(i.e., fluoride, chloride, bromide, iodide).

In the IUPAC system, alkyl halides are named as substituted alkanes. The substituent

prefix names for the halogens end with “o”(i.e.,“fluoro,”“chloro,”“bromo,”“iodo”).

Therefore, alkyl halides are often called haloalkanes.

PROBLEM 10

Give two names for each of the following compounds, and tell whether each alkyl halide is

primary, secondary, or tertiary:

a. c.

b. d. CH 3 CHCH 3

F

CH 3 CHCH 2 CH 2 CH 2 CH 2 Cl

CH 3

CH 3 CH 2 CHCH 3 Br

Cl

CH 3 CH 2 CHCH 2 CH 2 CHCH 3

Br

CH 3

2-bromo-5-methylheptane

CH 3

CH 3 CCH 2 CH 2 CH 2 CH 2 Cl

CH 3

1-chloro-5,5-dimethylhexane

4-bromo-2-chloro-1-methylcyclohexane

CH 3

Br

Cl

1-ethyl-2-iodocyclopentane

CH 2 CH 3

I

RCH 2 Br

a primary alkyl halide

RCH

Br

a primary carbon a secondary carbon

a secondary alkyl halide

R RC

Br

R

a tertiary alkyl halide

R

a tertiary carbon

methyl fluoride

CH 3 F

methyl chloride

CH 3 Cl

methyl bromide

CH 3 Br

methyl iodide

CH 3 I

Section 2.4 Nomenclature of Alkyl Halides 73

The number of alkyl groups attached to

the carbon to which the halogen is

bonded determines whether an alkyl

halide is primary, secondary, or tertiary.

CH 3 Cl

chloromethane

common name:

systematic name:

CH 3 CH 2 F

fluoroethane

CH 3 CHI

CH 3

2-iodopropane

CH 3 CH 2 CHBr

CH 3

2-bromobutane

methyl chloride ethyl fluoride

isopropyl iodide sec-butyl bromide

BRUI02-060_108r4 20-03-2003 11:47 AM Page 73