R2NH

R2NH denotes a secondary amine, a class of organic compounds in which a nitrogen atom is bonded to two carbon substituents and one hydrogen. The two R groups may be alkyl or aryl. Examples include dimethylamine (R = CH3) and diethylamine (R = CH2CH3); in unsymmetrical cases such as N-ethyl-N-phenylamine the two substituents differ.

The nitrogen in R2NH is typically sp3-hybridized and adopts a pyramidal geometry with a lone pair. R2NH acts as a Bronsted base and a nucleophile, forming ammonium salts R2NH2+ upon protonation and reacting at nitrogen with alkylating or acylating agents. The presence of the N–H bond influences hydrogen bonding and boiling points relative to tertiary amines of similar mass.

Reactions of secondary amines include alkylation to form tertiary amines (R3N) and, with excess alkylating agent, quaternary ammonium salts (R4N+). They can be acylated to give amides (R-CO-NR2). Secondary amines are commonly prepared by methods such as reductive amination of carbonyl compounds with primary amines followed by reduction, or by controlled alkylation of primary amines to stop at the secondary stage; hydrogenation of imines is another route. They are also susceptible to nitrosation, yielding N-nitrosamines under appropriate conditions.

In applications, R2NH compounds serve as solvents and intermediates in the synthesis of pharmaceuticals, polymers, and agrochemicals. They function as bases and ligands in catalysis and as building blocks in organic synthesis.

Safety considerations include potential irritant and toxic effects; appropriate ventilation and handling precautions are advised. Some secondary amines can form carcinogenic N-nitrosamines under nitrosating conditions, so exposure should be minimized.