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

Abstract 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·H 2 O salt is predicted to have the gauche structure as the predominant form at ambient temperature with NCCN and CNCC torsional angles of 110° and −123° as compared to 10° and −64°, respectively in the base lidocaine. The repulsive interaction between the two N–H bonds destabilized the gauche structure of lidocaine·HCl·H 2 O 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 1 H and 13 C NMR spectra of lidocaine·HCl·H 2 O were interpreted by experimental and DFT calculated chemical shifts of the lidocaine salt. The RMSD between experimental and theoretical 1 H and 13 C chemical shifts for lidocaine·HCl·H 2 O is 2.32 and 8.21 ppm, respectively.