Organic Chemistry

The nitrogen of an amine has the same geometry it has in ammonia (Section 1.12).

One, two, or three hydrogens may be replaced by alkyl groups. The number of hydro-

gens replaced by alkyl groups determines whether the amine is primary, secondary, or

tertiary (Section 2.7).

PROBLEM 19

Predict the approximate size of the following angles. (Hint: See Sections 1.11 and 1.12.)

a. the bond angle in an ether

b. the bond angle in a secondary amine

c. the bond angle in an alcohol

d. the bond angle in a quaternary ammonium salt

2.9 Physical Properties of Alkanes, Alkyl Halides,

Alcohols, Ethers, and Amines

Boiling Points

The boiling point (bp)of a compound is the temperature at which the liquid form of

the compound becomes a gas (vaporizes). In order for a compound to vaporize, the

forces that hold the individual molecules close to each other in the liquid must be over-

come. This means that the boiling point of a compound depends on the strength of the

attractive forces between the individual molecules. If the molecules are held together

by strong forces, it will take a lot of energy to pull the molecules away from each other

and the compound will have a high boiling point. In contrast, if the molecules are held

together by weak forces, only a small amount of energy will be needed to pull the mol-

ecules away from each other and the compound will have a low boiling point.

C¬N¬C

C¬O¬H

C¬N¬C

C¬O¬C

H H CH 3

CH 3 CH 3 CH 3

methylamine

a primary amine

sp^3 hybridized

dimethylamine

a secondary amine

N H N CH 3 N CH 3

trimethylamine

a tertiary amine

electrostatic potential maps for

methylamine dimethylamine trimethylamine

an ether

electrostatic potential

map for dimethyl ether

sp^3 hybridized

O

R

R

Section 2.9 Physical Properties of Alkanes, Alkyl Halides, Alcohols, Ethers, and Amines 81

3-D Molecules:

Methylamine;

Dimethylamine;

Trimethylamine

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