Ab initio HF, density functional and experimental studies on the IR spectra and structure of 1,2-benzisothiazol-3-(2H)-thione-1,1-dioxide (thiosacchanin) and its nitranion

Abstract

The spectral and structural changes taking place in the course of the conversion of 1,2-benzisothiazol-3-(2H)-thione-1,1-dioxide (thiosaccharin) into a nitranion have been studied on the basis of both IR spectra and ab initio HF 6-31G(d) and BLYP 6-31G(d,p) force field calculations. The conversion causes ν SO 2 as and ν SO 2 s frequency decreases of 47 and 13 cm −1, respectively, and other spectral changes. The ν CS coordinate is strongly delocalized. The ab initio geometries of the isolated molecule and nitranion agree well with the single-crystal X-ray ones, determined for thiosaccharin and its sodium (potassium) monohydrate salts, respectively. The nitranionic charge is delocalized almost uniformly within the thiocarbonyl (0.29 e −), sulfonyl (0.24 e −), and phenylene (0.24 e −) groups, and the nitranionic center (0.23 e −).