LOW RESOLUTION MICROWAVE SPECTROSCOPY .14. CONFORMATIONS OF S-ISOPROPYL THIOESTERS AND A HIGH-RESOLUTION STUDY OF S-ISOPROPYL THIOFLUOROFORMATE

A high resolution microwave assignment of S-isopropyl fluorothioformate yielded the following rotational constants: A0 = 4196(1) MHz, B0 = 1374.23(3) MHz and C0 = 1159.80(4 MHz, compatible with a syn-gauche (τ1(OCSC) = 0°, τ2(CSCH) ∼ 40°) conformer. Low resolution microwave spectra of S-isopropyl trifluorothioacetate, cyanothioformate and chlorothioformate each display strong a-type band series compatible with either syn-syn (τ1(OCSC) = 0°, τ2(CSCH) = 0°) or syn-gauche (τ1(OCSC) = 0°, τ2(CSCH) ∼ 60°) conformers. Experimental B+C values are 1211.7(6), 1839.6(7) and 1814.6(5), (1774.4(5), 37Cl) MHz for the trifluorothioacetate, cyanothioformate and chlorothioformate, respectively. S-isopropyl trifluorothioacetate also displays a weak band series with a B+C value of 1310.2(5) MHz compatible with a syn-anti (τ1(OCSC) = 0°, τ2(CSCH) = 180°) structure. Torsionally excited species freely rotating about τ2 have been previously observed in S-ethyl thioesters but are not observed in S-isopropyl thioesters indicating a higher torsional barrier for the S-isopropyl compounds. © 1979.