urethane

Carbamates, or urethanes, are a group of organic compounds sharing a common functional group with the general structure R¹-O-(CO)NR²-R³. Carbamates are esters of carbamic acid, NH₂COOH, an unstable compound with R¹ = R² = R³ = H. Carbamic acid is an unstable compound because of the lability of the H-groups, leading upon exposure to water to rearrangements that lead to the decomposition to ammonium bicarbonate. Since carbamic acid contains a nitrogen attached to a carbonyl group, it is also has amide character, although carbamates behave differently than most amides. Therefore, carbamate esters may have alkyl or aryl groups substituted on the nitrogen, or the amide function. For example, ethyl carbamate (trivial name "urethane"), is unsubstituted, whereas ethyl N–methylcarbamate has a methyl group attached to the nitrogen (see methyl isocyanate for formation of N-methylcarbamates).