Molecular structures, conformations, and vibrational spectra of bicyclo[3.1.0]hexane and its oxygen analogues

The molecular structures and ring-puckering potential energy profiles of bi cyclo[3.1.0]hexane and its three oxygen analogues-6-oxabicyclo[3.1.0]hexane , 3-oxabicyclo[3.1.0]hexane, and 3,6-dioxa[3.1.0]hexane-have been reexamine d using both ab initio (HF and MP2) and density functional theory (B3LYP) m ethods. The calculated structural parameters and ring-puckering potential p rofiles of those molecules have been compared to the previously reported mi crowave, electron diffraction, and far-infrared data. Our computational res ults show that the inclusion of electron correlation effects is crucial for the precise prediction of geometrical parameters of such bicyclic systems. The calculated ring-puckering potential energy profiles using the B3LYP me thod reproduce the experimental profiles more accurately than those predict ed by MM3 force-field methods. Vibrational frequency calculations of 6-oxab icyclo[3.1.0]hexane have been also performed to compare with those measured from the infrared and Raman spectroscopy. Comparison of the calculated and experimental results indicates that the B3LYP method has led to the predic tion of more accurate vibrational frequencies than the HF and MP2 methods. (C) 2000 Elsevier Science B.V. All rights reserved.