The Foundations of Chemistry

higher temperatures, or in the presence of sunlight or other sources of ultraviolet light,

H atoms in the hydrocarbon can be replaced easily by halogen atoms. These substitution

reactions are called halogenationreactions.

The reaction is represented as

Many organic reactions produce more than a single product. For example, the chlori-

nation of CH 4 may produce several other products in addition to CH 3 Cl, as the following

equations show.

When a hydrocarbon has more than one C atom, its reaction with Cl 2 is more complex.

The first step in the chlorination of ethane gives the product that contains one Cl atom

per molecule.

When a second hydrogen atom is replaced, a mixture of the two possible products is

obtained.

Cl Cl H

H

H

 C HCl

heat or

UV

ethane chloroethane

(ethyl chloride)

bp  13.1C

H

CCl

H

HH

H

H

C

H

C

H

CClCl

Cl

Cl Cl

H

Cl C Cl

Cl

Cl

 HCl

tetrachloromethane

(carbon tetrachloride)

bp  76.8C

H

Cl CClCl Cl

H

Cl

H

C Cl

Cl

 HCl

trichloromethane

(chloroform)

bp  61 C

H

H

H CClCl Cl Cl

H

H

 C Cl HCl

dichloromethane

(methylene chloride)

bp  40.2C

H

H

H

CClClH H

H

H

 C Cl HCl

heat or

UV

methane chlorine chloromethane

(methyl chloride)

bp  23.8C

Note that only one half of the chlorine
atoms occur in the organic product.
The other half form hydrogen
chloride, a commercially valuable
compound.

1086 CHAPTER 27: Organic Chemistry I: Formulas, Names, and Properties