Molecular Structure, Vibrational Spectra and Potential Energy Distribution of Colchicine Using ab Initio and Density Functional Theory

Abstract

This work is devoted to theoretical study on molecular structure of protopine. The equilibrium geometry, harmonic vibrational frequencies and infrared intensities were calculated by ab initio Hartree–Fock and density functional B3LYP methods with the 6-31G(d) basis set and were interpreted in terms of potential energy distribution (PED) analysis. The internal coordinates were optimized repeatedly for many times to maximize the PED contributions. A detailed interpretation of the infrared spectra of protopine is reported. The calculations are in agreement with experiment. The thermodynamic functions of the title compound were also performed at HF/6-31G(d) and B3LYP/6-31G(d) level of theory. The FT-IR spectra of protopine were recorded in solid phase.