Knowledge Bank

Thiacyclobutane, [FIGURE] is one of the compounds included in the program of API Research Project 48A for studying the thermodynamic properties of sulfur compounds of interest in petroleum technology. It was necessary to have a vibrational assignment for this compound and a knowledge of its molecular symmetry in order to compute tables of the thermodynamic functions. Calorimetric values of the entropy and heat capacity of the vapor were available to guide in the selection of the fundamental frequencies. The Raman and infrared data for thiacyclobutane were interpreted most satisfactorily on the basis of a planar-ring structure of $C2v$ pointgroup symmetry. The frequency of the out-of-plane ring bending mode did not appear in the spectra. A value of about $75cm-1$ for this frequency was required to fit the experimental entropy; several weak Raman lines and infrared bands which could be interpreted as sumcombinations involving a $75cm-1$ fundamental tended to confirm that value. The assignment adopted is given below. Asterisks denote the few frequencies which were not definitely assignable from the spectra and which were selected somewhat arbitrarily to fit the calorimetric heat capacity value. $$\begin{array}{lcccc}&A_{1}& B_{1} & A_{2} & B_{2}\Ring\ bending &528&&& 75\C - S\ stretching& 698& 675\ CH_{2}\ rocking &&& 878 & 844 & 969\ C - C\ stretching &932 & 991\ CH_{2}\ wagging &1226 & 1173 & 1326^{\ast}\ CH_{2}\ twisting &&&1205^{\ast} & 1303^{\ast} & 1272\ CH_{2}\ bending & 1440 & 1460 &1440\C - H\ stretching &\multicolumn{4}{r}{Six\ frequencies\ near\ 2950\ not\ assigned\ in\ detail}\end{array}.$$