Methylthio- (MTE) and bis-methylthioethyne (BMTE) molecules are calculated
by the SCF MO method (geometry optimization, basis set 6-31G*/MP2). The cal
culated internal rotation barriers of methyl groups are 7.12 kJ/mole for MT
E and 12.86 kJ/mole for BMTE (both groups are simultaneously rotated). The
s-gosh-orientation of the thiomethyl fragments corresponds to a stable conf
ormation of BMTE. The estimated values of the s-cis- and s-trans-barriers o
f mutual rotation of SCH3 groups about the an's of the C=C bond are 13.61 a
nd 12.54 kJ/mole, respectively. Conformationally sensitive MOs and vibratio
n frequencies are established. An analysis of the experimental IR absorptio
n and Raman spectra and the calculated vibrational spectrum makes it possib
le to conclude that in the liquid phase the BMTE molecules also have an s-g
osh-conformation.