Crystal structure and conformational flexibility of 2-(acetylamino) prop-2-enoic acid (N-acetyldehydroalanine)

The molecular structure of N-acetyldehydroalanine (2-acetylaminoprop-2- enoic acid) has been determined from three-dimensional X-ray data. C <inf>5</inf>H<inf>7</inf>NO<inf>3</inf> is monoclinic, space group P2 <inf>1</inf>/n, with Z = 4 in a cell of dimensions a = 14.904(7), b = 10.162(6), c = 3.943(3) Å, β = 91.7(1)°. The structure was solved by direct methods and refined by full-matrix least-squares to R 0.060 for 1 350 observed reflections. The molecules exhibit a fully planar conformation and are linked by OH⋯O hydrogen bonds to form one-dimensional chains. The conformational flexibility is discussed on the basis of ab initio and empirical calculations.