X-ray, MP2 and DFT studies of the structure and vibrational spectra of trigonellinium chloride

The effects of hydrogen bonding, inter- and intramolecular electrostatic interactions on the conformation of trigonellinium. chloride, TRGH (.) Cl, in the crystal and on that of a single molecule have been studied by X-ray diffraction, FT-IR, Raman, H-1 and C-13 NMR spectroscopies, and by MP2 and DFT calculations. In the crystal, the Cl- anion is connected with protonated trigonelline via hydrogen bond, O-H (. . .) Cl- = 2.915(3) Angstrom, and three N+ (.) (.) (.) Cl- intermolecular electrostatic interactions. In a single molecule, the Cl- anion is also engaged in a slightly longer hydrogen bond, O-H (. . .) Cl- = 2.948-3.019 Angstrom, but only in one type of intramolecular electrostatic interaction. The optimized bond lengths and bond angles at the MP2 and B3LYP levels of theory are in good agreement with the X-ray data, except conformation of the COOH group, which is cis (syn) in the crystal and trans (anti) in the single molecule. The probable assignments for the experimental solid state vibrational spectra of TRGH (.) Cl and TRGD (.) Cl based on the calculated MP2/cc-pVDZ frequencies and intensities were made. The effect of quaternization of nicotinic acid, its salt and amide on chemical shifts of the ring protons and carbons is analyzed. (C) 2003 Elsevier Science B.V. All rights reserved.