Spectra and structure of small ring compounds. XLII. Microwave spectrum of 2,5-dihydrothiophene

Abstract

The microwave spectrum of 2,5-dihydrothiophene CHCHCH2SCH2 has been recorded from 18.0 to 39.0 GHz. Only a-type R branches were observed and assigned for the ground and five excited states of the ring puckering motion. The ground state rotational constants are A=6621.59±0.12, B=4798.42±0.03, and C=2885.27±0.01 MHz. These rotational constants are shown to be consistent with the reasonably proposed structural parameters for this molecule. The quantity Ia+Ib−Ic=6.487 U Å2 is shown to arise from the four out-of-plane hydrogen atoms and the heavy atom skeleton is, therefore, shown to be planar. The dipole moment was determined from the Stark effect to be ‖μa‖=‖μt‖=1.75±0.01 D. These results are compared to the corresponding quantities for similar molecules.