γ-Aminobutyric Acid: a Novel Tetragonal Phase

In the tetragonal phase of γ-aminobutyric acid, C4H9NO2, the single type of molecule adopts a partially folded zwitterionic form. Whereas in the previously characterized monoclinic phase the partially folded zwitterionic mol­ecules exhibit a gauche conformation with respect to the C2—C3 bond, in this phase the molecules exhibit a trans conformation. The altered pattern of intramolecular N⋯O distances may be of significance with respect to the neurotransmission behavior of this substance. In addition to three strong hydrogen bonds involving the three H atoms bound to the N atom, as in the monoclinic phase, there is a fourth weaker one which results in a two-center bifurcated bond. There is also evidence suggestive of an intramolecular bridging hydrogen bond involving the N atom, an O atom and a methylene H atom, as previously proposed as a stabilizing factor for the gauche conformation observed in the monoclinic phase.