Crystal structure analysis of N-acetylated proline and ring-size analogs.

Crystal structures of N-acetylated proline and homologs with four- and six-membered rings (azetidine carboxylic acid and piperidine carboxylic acid) were obtained and compared. The distinctly different conformations of the four-, five-, and six-membered rings reflect Bayer strain, n→π* interaction, and allylic strain, and result in crystal lattices with a zig-zag structure.