Crystal and molecular structure of N-methylpiperidine betaine hydrochloride

Abstract

A 1:1 complex between N-methylpiperidine betaine and hydrochloric acid, MPBH·Cl, has been characterized by single crystal X-ray analysis, FTIR spectroscopy, and DFT calculations. The crystals are monoclinic, space group P2 1/ n, with a=6.0644(3), b=13.0220(6), c=12.7653(7) A ̊ , β=101.925(5)°. The piperidine ring adopts a chair conformation with the –CH 2COOH group in an axial and the-CH 3 group in an equatorial position. In the crystal, the Cl −anion is engaged in a medium-strong hydrogen bond with the COOH group (O–H⋯Cl −=2.9503(7) Å), in several C–H⋯Cl − contacts and, additionally, in three N +⋯Cl −intermolecular interactions. Four conformations (axial and equatorial, both protonated and unprotonated) of MPBHCl were examined by the B3LYP/6-31G(d,p) method. The calculated structure of MPBH·Cl(ax) is very similar to that in the crystal, except the N(1)–C(8)–C(9)–O(1) and N(1)–C(8)–C(9)–O(2) units, which are planar in the crystal but nonplanar in the isolated molecule. Powder FTIR spectra of MPBH·Cl and its deuterated analogue (MPBD·Cl) were measured and assignments of the observed bands to vibrations of the hydrogen bond and to internal vibrations are proposed.