## Abstract

5,6-Dihydro-2H-thiopyran, CH_{2}CH_{2}CH=CHCH_{2}S, has been synthesized and its far-infrared and Raman spectra recorded. Two series of sharp bands were observed originating from 139 and 235 cm^{-1} in the infrared spectrum for the out-of-plane ring-bending and the ring-twisting vibrations, respectively. A detailed energy level diagram including numerous excited states was determined for the two coupled vibrations. The two-dimensional potential energy surface, which satisfactorily fits more than two dozen observed transitions, was calculated to be V = 2.431 × 10^{4}x^{4}_{1} - 0.383 × 10^{4}x _{1}^{2} + 2.258 × 10^{4}x_{2}^{4} - 1.966 × 10^{4}x_{2}^{2} + 1.026 × 10 ^{5}x_{1}^{2}x_{2}^{2}, where x _{1} is the ring-bending coordinate and x_{2} is the ring-twisting coordinate. The minimum energy on the potential surface corresponds to a twisting angle of 37.8° (the half-chair conformation). The lowest energy bent (boat) conformation corresponds to a saddle point 4130 cm^{-1} above the twisted conformation on the potential energy surface. The results are compared to analogous molecules and to molecular mechanics calculations.

Original language | English |
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Pages (from-to) | 2771-2775 |

Journal | Journal of Chemical Physics |

Volume | 91 |

State | Published - 1989 |