The molecular structure and vibrational, 1H and 13C NMR spectra of lidocaine hydrochloride monohydrate

The structure, vibrational and NMR spectra of the local anesthetic drug lidocaine hydrochloride monohydrate salt were investigated by B3LYP/6-311G** calculations. The lidocaine-HCl center dot H2O salt is predicted to have the gauche structure as the predominant form at ambient temperature with NCCN and CNCC torsional angles of 110 degrees and -123 degrees as compared to 10 degrees and -64 degrees, respectively in the base lidocaine. The repulsive interaction between the two N-H bonds destabilized the gauche structure of lidocaine center dot HCl center dot H2O salt. The analysis of the observed vibrational spectra is consistent with the presence of the lidocaine salt in only one gauche conformation at room temperature. The H-1 and C-13 NMR spectra of lidocaine.HCl center dot H2O were interpreted by experimental and DFT calculated chemical shifts of the lidocaine salt. The RMSD between experimental and theoretical H-1 and C-13 chemical shifts for lidocaine center dot HCl center dot H2O is 232 and 8.21 ppm, respectively. (C) 2015 Elsevier B.V. All rights reserved.