A VALENCE FORCE FIELD FOR ALIPHATIC SULFUR COMPOUNDS - ALKANETHIOLS AND THIOALKANES

For the purpose of accurate statistical thermodynamic calculations, which require reliable vibrational assignments, a valence force field for aliphatic sulfur compounds was obtained. The 33-force-constant field was derived from 363 observed vibrational wave numbers of the following 11 molecules: Methanethiol, 2-thiapropane, ethanethiol, 2-thiabutane, 1-propanethiol, 2-propanethiol, 3-thiapentane, 3-methyl-2-thiabutane, 2-methyl-2-propanethiol, 3,3-dimethyl-2-thiabutane, and cyclohexanethiol. The mean deviation of the calculated wave numbers from the observed ones is 9.4 cm-1 or 0.87%. To test the transferability of this field, and hence its utility for analyzing the molecular spectra of other aliphatic sulfur compounds, it was used for calculations for four additional compounds: 2-methyl-1-propanethiol, 2-butanethiol, 2-methyl-2-butanethiol, and 2,4-dimethyl-3-thiapentane. The agreement between observed and calculated wave numbers is as good as that for the 11 compounds used in deriving the field, which proves that the derived field is indeed transferable among the group of aliphatic sulfur compounds. Previous assignments for the molecules investigated were critically reexamined in the course of the molecular vibrational analysis and revised as necessary, and the probable stable conformations of these molecules are presented and discussed. © 1969.