Knowledge Bank

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), $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl)(2472.8(6),v=1;2413(1),v=1,37C1)$ and 2368(3) (2314(3), $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl)$ 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), $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}$Cl) MHz compatible with a syn-gauche ($\tau 1(OCSC)=0\circ ,\tau 2$ (CSCH) $\sim 60\circ$).""