AB-INITIO PREDICTION OF VIBRATIONAL ABSORPTION AND CIRCULAR-DICHROISMSPECTRA OF CHIRAL NATURAL-PRODUCTS USING DENSITY-FUNCTIONAL THEORY - ALPHA-PINENE

Ab initio density functional theory (DFT) is used to analyze the vibra tional unpolarized absorption and circular dichroism spectra of the ch iral monoterpene, alpha-pinene. Large (TZ2P) basis set calculations us ing the hybrid functionals B3PW91 and B3LYP are in excellent overall a greement with experiment and permit the assignment of a large fraction of the fundamental frequencies, The quantitative accuracy of DFT in p redicting the frequencies, dipole strengths, and rotational strengths of the fundamentals of alpha-pinene is documented for the B3PW91 and B 3LYP functionals at both TZ2P and 6-31G basis set levels. Hartree-Foc k/self-consistent field (HF/SCF) calculations have also been carried o ut in parallel. The accuracy of the HF/SCF methodology is markedly inf erior to that of DFT. In particular, HF/SCF predictions of the vibrati onal circular dichroism (VCD) spectrum of alpha-pinene are in very poo r agreement with experiment.