A strong dependence of the CH 3 internal rotation barrier on conformation in thioacetic acid: Microwave measurements and an energy decomposition analysis

C. J. Smith, Anna K. Huff, Huaiyu Zhang, Yirong Mo, Kenneth R. Leopold

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Abstract

Rotational spectra of thioacetic acid (CH 3 COSH) have been observed by pulsed-nozzle Fourier transform microwave spectroscopy. Spectroscopic constants are reported for both the syn and anti conformers of the parent species, as well as the 34 S and 13 C carbonyl isotopologues. Transitions arising from the lowest A and E internal rotor states of the methyl group have been observed and analyzed. Experimental values of the three-fold internal rotation barrier, V 3 , for the syn and anti conformers of the parent isotopologue are 76.300(12) and 358.056(51) cm −1 , respectively, indicating a large effect of the S−H orientation on the CH 3 internal rotation potential. M06-2X/6-311+G(d,p) calculations are in good agreement with these results. The block localized energy decomposition method has been applied to understand the origins of this strong dependence of V 3 on conformation. The results indicate that π conjugation from the SH to the carbonyl group and steric repulsion between the SH and the methyl group in the anti form are main contributors to the difference.

Original languageEnglish (US)
Article number134302
JournalJournal of Chemical Physics
Volume150
Issue number13
DOIs
StatePublished - Apr 7 2019

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation (Grant No. CHE 1563324) and the Minnesota Supercomputing Institute. Anna Huff was supported by a Lester C. and Joan M. Krogh Fellowship, administered through the University of Minnesota.

Funding Information:
This work was supported by the National Natural Science Foundation of China (Grant Nos. 11374066 and 11374068).

Publisher Copyright:
© 2019 Author(s).

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