Role of sulfurdorbitals in isothiocyanic acid and an electronichyphen;structure comparison with isocyanic acid

摘要

The electronic structure of isothiocyanic acid, HNCS, was determined by anab initioLCAOhyphen;MOhyphen;SCF calculation. Isocyanic acid, HNCO, was also calculated and the two molecules are compared. The basis set consisted of uncontracted, atomhyphen;optimized Gaussian functions, with ninesplus fivepexponents to describe the sulfur and fivesplus twopapiece for the carbon, nitrogen, and oxygen. The hydrogen was represented by threeshyphen;type functions. An additional calculation of HNCS was carried out by adding adset to the description of the sulfur. The molecular orbitals of HNCS are analyzed using simple perturbation theory applied to the localized valencehyphen;bond functions and the SCF orbitals are displayed using planar electronhyphen;density plots. The electronic structure of HNCS is compared with that of HNCO and it is concluded that (1) the pgr; system in HNCS involves a nitrogen lone pair stabilized by a higherhyphen;lying Csngbnd;S pgr; bond while the pgr; system of HNCO consists of a Csngbnd;O pgr; bond stabilized by the higherhyphen;energy nitrogen lone pair and (2) thedorbitals of sulfur are accepting density in a sgr; rather than a pgr; fashion.