VIBRATIONAL SPECTROSCOPY AND CONFORMATIONAL STUDIES OF 1,4-BENZODIOXAN - AB-INITIO AND DENSITY-FUNCTIONAL CALCULATIONS

The gas-phase infrared and pure-liquid Raman spectra of 1,4-benzodioxa n have been recorded and analyzed. The infrared vibrational frequencie s, absolute intensities, and ring-inversion potential energy profile o f the molecule have been also predicted using Becke's three-parameter hybrid (B3LYP) method in the density functional theory (DFT) method, a s well as the Hartree-Fock (HF) and molecular mechanics (MM3) methods. The vibrational frequencies calculated at the B3LYP levels agree much better with the observed frequencies than those predicted by the HF o r MM3 methods. The enlargement of basis sets at the B3LYP levels has i mproved the accuracy of calculated Vibrational frequencies. The ring-i nversion process of 1,4-benzodioxan between the twist and bent conform ers has also been investigated using the DFT, HF, and MM3 methods. The calculated results at the B3LYP/6-31G level indicate that the twiste d conformer has a lower energy than the bent conformer and that the en ergy difference between the two forms is 7.5 kcal/mol. This value is 1 .3 kcal/mol lower than the barrier of nonbenzene-fused ring 1,4-dioxen e. (C) 1998 Elsevier Science B.V. All rights reserved.