X-ray mapping in heterocyclic design. I. Diffractometric study of crystalline 1,2-dihydro-2-imino-1-carboxymethylpyridine monohydrate: Structural evidence for the zwitterionic character of the molecule

A single-crystal X-ray diffraction analysis of 1,2-dihydro-2-imino-1-carbox ymethylpyridine is carried out. The transparent colorless crystals are orth orhombic, and the unit-cell parameters are as follows: a = 5.026(1) Angstro m, b = 12.320(7) Angstrom, c = 25.551(1) Angstrom, space group Pbca. The st ructure is solved and refined to R-1 = 0.0562. In the six-membered heterocy cle, the partially ordinary bonds alternate with the partially double bonds . The plane of the carboxylate group is almost perpendicular to the plane o f the pyridine ring, and the existence of intramolecular hydrogen bonds bec omes impossible. The crystal structure involves an extended system of inter molecular bonds, including those with the participation of water molecules.