Crystal and molecular structure of quinuclidine betaine hydrochloride studied by X-ray diffraction, DFT, FTIR, and NMR methods

Quinuclidine betaine hydrochloride (1-carboxymethyl-1-azabicyclo[2.2.2]octane hydrochloride, QNBH·Cl) has been synthesized and characterized by X-ray diffraction, FTIR and NMR spectroscopy, and DFT calculations. QNBH·Cl crystallizes in orthorhombic space group Pnma. In the crystal the Cl− anion is engaged in a medium-strong COOH·Cl hydrogen bond of 2.921(2) Å, in which the acidic proton is closer the carboxylate group and additionally in some C-H···Cl contacts, stabilizing the crystal structure. The atoms of the quinuclidine betaine are located on a mirror plane. The structure of QNB·HCl optimized at the B3LYP/6-31G(d,p) level of theory is consistent with the X-ray structure, however the O···H-Cl hydrogen bond is somewhat shorter, 2.895 Å. The FTIR spectra of QNBH·Cl and QNBD·Cl have been measured and the bands have been assigned to vibrations of the hydrogen bond. The 1H and 13C NMR chemical shifts correlate linearly with the calculated magnetic isotropic shielding tensors.