Crystal structure and vibrational spectrum of N-methylpiperidine betaine hexafluorosilicate

A study of a series of benzoylthioureas with 3,3-disubstitution has been carried out by means of theoretical calculations. X-ray diffraction data (XRD), semiempirical and ab initio Hartree-Fock calculations demonstrated that the most stable conformation for these molecules is the so-called `Sʹ. Also an explanation of the high selectivity towards the Salkylation of the systems, based on the high contribution of the sulphur atom to the HOMO in acylthioureas is given for the title compounds. Geometries were optimized at the AM1 and HF/6-31G* levels and subsequently the results were compared with experimental XRD.