LOW RESOLUTION MICROWAVE SPECTROSCOPIC STUDIES OF ETHYL AND ISOPROPYL THIOESTERS
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Date
1977
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Volume Title
Publisher
Ohio State University
Abstract
Low resolution microwave (LRMW) spectra of ethyl trifluorothioacetate display a-type band series characterized by B + C values of 1599.2(2) (1593.2(3), v = 1; 1584.5(6), v = 2) and 1554(1) MHz associated with two rotamers designated compact and intermediate, respectively. Ethyl chlorothioformate displays band spectra of three conformers with B + C values of 2171(3); 2486.2(6) (2428(1), $^{37}Cl) (2472.8(6), v = 1; 2413(1), v = 1, ^{37}C1)$ and 2368(3) (2314(3), $^{37}Cl)$ MHz for rotamers designate extended, compact: and intermediate, respectively. Rotational constants of extended ethyl chlorothioformate are consistent with a syn-anti $(\tau_{1}(OCSC) = 0^\circ ,\tau_{2}(CSCC)= 180^\circ)$ structure. Rotational constants of the compact conformer of both compounds are consistent with a syn-gauche $(\tau_{1}(OCSC) = 0^\circ, \tau_{2}$ (CSCC) $\sim 90^\circ)$ structure and the intermediate species with a gauche-gauche $(\tau_{1}$ (OCSC) $\sim 60^\circ, \tau_{2}$ (CSCC) $\sim 240^\circ)$ structure. From this temperature dependence of the band intensities the relative energies of the extended, compact and intermediate ethyl chlorothioformate are 0, $\sim -0.5$, and $\sim$ 2.0 kcal/mole, respectively. The intermediate conformer of ethyl trifluorothioacetate is $\sim$ 2.5 kcal/mole higher in energy than the compact form. In both cases, the spectrum of the intermediate conformer is anomalously intense. Two a-type band series having B + C values of 1211.7(5) and 1310.2(5) MHz are present in LRMW spectra of isopropyl trifluorothioacetate, These rotational constants are consistent with syn-gauche ($\tau_{1}(OCSC) = 0^\circ, \tau_{2}(CSCH) = 60^\circ$ and syn-anti ($\tau_{1}(OCSC) = 0^\circ, \tau_{2}(CSCH) = 180^\circ$) conformers, respectively. The syn-anti conformer is approximately 0,5 kcal/mole higher in energy. LRMW spectra of isopropyl chlorothioformate are consistent with one conformer having a B + C value of 1814.6(5) (1774.4(5), $^{37}$Cl) MHz compatible with a syn-gauche ($\tau_{1}(OCSC) = 0^\circ, \tau_{2}$ (CSCH) $\sim 60^\circ$).""
Description
Author Institution: Department of Chemistry, The University of Connecticut