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Amines

Key Concepts

Amines contain the -NH₂ functional group.
Amines can be classified as :

primary : general formula R-NH₂
secondary : general formula R-NH-R'
tertiary : general formula R'-NR-R"

Amines are named by adding the suffix amine to the corresponding alkyl group of the molecule:

Number the longest carbon chain giving the amine functional group the lowest number.
Name the carbon chain.
Add the suffix -amine

Properties of Amines :

Amines are polar molecules and are soluble in water.
Amines are weak bases.
Amines have a distinctive, often unpleasant, odour.

Amines react with inorganic acids to form salts

Naming and Classification of Amines

name	formula	general formula	classification
methylamine	CH₃NH₂	R-NH₂	primary
dimethylamine	(CH₃)₂NH	R-NH-R'	secondary
trimethylamine	(CH₃)₃N	R'-NR-R"	tertiary
ethylamine	CH₃CH₂NH₂	R-NH₂	primary
propylamine	CH₃CH₂CH₂NH₂	R-NH₂	primary

Properties of Amines

name	formula	boiling point (^oC)	solubility in water	K_b
methylamine	CH₃NH₂	-7.5	soluble	4.4 x 10^-4
dimethylamine	(CH₃)₂NH	7.5	soluble	5.2 x 10^-4
trimethylamine	(CH₃)₃N	3	soluble	5.0 x 10^-5
ethylamine	CH₃CH₂NH₂	17	soluble	4.7 x 10^-4
propylamine	CH₃CH₂CH₂NH₂	48	soluble	5.1 x 10^-4

Amines can undergo hydrogen bonding though the N-H bond.
Nitrogen is less electronegative than O, therefore the NH bond is less polar than an OH bond and the hydrogen bonding in amines is weaker than in compounds with OH groups.

The boiling points of amines falls between those for non-hydrogen bonded compounds like alkanes, and those for strongly hydrogen bonded compounds like alkanols (alcohols) or carboxylic (alkanoic) acids.

Amines are water soluble because amines can form hydrogen bonds with water molecules.

Amines are weak bases, the base dissociation constant, K_b, is small.