Molecular structure of p-methyl benzene sulphonyl halides and benzene sulphonyl chloride from quantum-mechanical calculations and gas-phase electron diffraction

The molecular structure and conformations of p-methyl benzene sulphonyl hal ides (4-CH3PhSO2F/Cl/Br) have been investigated by ab initio calculations a t the HF/6-311G** level, semiempirical PM3 calculations and by gas-phase el ectron diffraction. MNDO, AM1, PM3 semiempirical and nb initio calculations with various basis sets have been applied to obtain of molecular structure of benzene sulphonyl chloride. Comparative analysis of theoretical results with available electron diffraction data has been done to find out methods and basis sets which give reliable prediction of geometrical parameters of aryl sulphonyl derivatives. Only the PM3 model provides good agreement bet ween calculated and experimental geometrical parameters from the set of sem i-empirical methods. The bond lengths and angles obtained from ab initio ca lculations using the 6-31G** and 6-311G** split-valence basis sets with pol arization functions are very close to the results from the electron diffrac tion study. It was found that benzene sulphonyl chloride and all of the inv estigated p-methyl benzene sulphonyl halides have C-S symmetry with orthogo nal position of S-Hal bond projection relative to benzene ring plane. The h eight of the internal rotation barrier of the sulphonyl group of benzene su lphonyl chloride has been found to be 6.5 kJ/mol from PM3 calculations. For p-methyl benzene sulphonyl halides the internal rotation barrier height of the group increases of halogen size: 6.0 kJ/mol, 6.7 kJ/mol and 9.8 kJ/mol for Hal=F, Cl and Br, respectively. PM3 calculations of internal rotation barrier height of methyl group in p-methyl benzene sulphonyl halides gave t he values in the range 0.10 kJ/mol -0.14 kJ/mol and ab initio 6-311G** calc ulations provided still lower values.