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Chemistry · Glossary

What is Hemiaminals, imines and enamines?

Also known as: hemiaminal · imine · enamine

Definition 23.5 University Chemistry — Year 2 · Chapter 23 — Amines and Nitrogen Compounds

A primary amine adds to an aldehyde or a ketone to give a hemiaminal (a carbon bearing OH\ce{OH} and NHR\ce{NHR}); its dehydration gives an imine R2C=NR′\mathrm{R_2C{=}NR'}. A secondary amine, which cannot form a neutral imine, gives after dehydration an enamine R2C=CR−NR2′\mathrm{R_2C{=}CR{-}NR'_2}, the double bond moving to the adjacent carbon.

Formation of an imine: nucleophilic addition of the amine to the carbonyl gives the hemiaminal; acid catalysis turns its OH into a leaving group (-OH2+), water leaves and the nitrogen lone pair forms the C=N double bond. Every step is reversible: water in excess hydrolyses the imine back.
Formation of an imine: nucleophilic addition of the amine to the carbonyl gives the hemiaminal; acid catalysis turns its OH\ce{OH} into a leaving group (−OHX2X+\ce{-OH2+}), water leaves and the nitrogen lone pair forms the C=N\ce{C=N} double bond. Every step is reversible: water in excess hydrolyses the imine back.
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