Crystal and molecular structure of 4-carboxypiperidinium chloride (4-piperidinecarboxylic acid hydrochloride)

4-Piperidinecarboxylic acid hydrochloride, 4PCAH·Cl, has been characterized by single crystal X-ray diffraction, B3LYP/6-31G(d,p) calculations, and FTIR spectrum. The crystals of the title compound at room temperature are orthorhombic, space group P212121, with a = 7.0504(4), b = 7.5070(5), c = 15.3110(9) Å, V = 810.37(9) Å3, and Z = 4. The piperidine ring is protonated and adopts a chair conformation with the COOH group in the equatorial position. In the crystal structure, the Cl− anion is connected with the carboxyl group via an OCOH⋯Cl− hydrogen bond of 3.022(2) Å. The Cl− anion is additionally engaged in two N(1)+H⋯Cl− hydrogen bonds (3.168(2) and 3.186(2) Å) and one relatively short N(1)+⋯Cl− electrostatic interaction (4.603(2) Å). Five conformers of the title compound have been examined by the B3LYP/6-31G(d,p) method. Powder FTIR spectra of the title compound and its deuterated analogue are consistent with the X-ray structure.