Gabapentin and gabapentin monohydrate.

Gabapentin [1-(aminomethyl)cyclohexaneacetic acid, C9H17NO2] is a zwitterion in the solid state. Its crystal structure involves extensive hydrogen bonding between the NH3(+) and COO(-) groups of neighboring molecules. The structure of gabapentin monohydrate [1-(aminomethyl)cyclohexaneacetic acid monohydrate, C9H17NO2-H2O] also involves such hydrogen bonding and, in addition, has a hydrogen-bonding network comprising the water molecules and both the NH3(+) and COO(-) groups.