Vibrational spectra and potential energy surface for the ring bending and ring twisting of 5,6hyphen;dihydrohyphen;2Hhyphen;thiopyran

摘要

5,6hyphen;Dihydrohyphen;2Hhyphen;thiopyran, CH2CH2CH=CHCH2S, has been synthesized and its farhyphen;infrared and Raman spectra recorded. Two series of sharp bands were observed originating from 139 and 235 cmminus;1in the infrared spectrum for the outhyphen;ofhyphen;plane ringhyphen;bending and the ringhyphen;twisting vibrations, respectively. A detailed energy level diagram including numerous excited states was determined for the two coupled vibrations. The twohyphen;dimensional potential energy surface, which satisfactorily fits more than two dozen observed transitions, was calculated to beV=2.431times;104x41minus;0.383times;104x21+2.258times;104x42minus;1.966times;104x22+1.026times;105x21x22, wherex1is the ringhyphen;bending coordinate andx2is the ringhyphen;twisting coordinate. The minimum energy on the potential surface corresponds to a twisting angle of 37.8deg; (the halfhyphen;chair conformation). The lowest energy bent (boat) conformation corresponds to a saddle point 4130 cmminus;1above the twisted conformation on the potential energy surface. The results are compared to analogous molecules and to molecular mechanics calculations.