A B Initio and Indo Molecular Orbital Calculations of the Geometries and Electronic Structures of Substituted Sulfines

Molecular orbital calculations are presented for the parent sulfine and some monoand dihalogensubstituted sulfines, using ab initio and INDO methods. A partial geometry optimization was performed for nine different sulfines. Charge distributions, potential surfaces and dipole moments were calculated from the wave functions of the optimized geometries. Cis-trans interconversion barriers and electronic spectra are also given. The atomic charges of the S and 0 atoms are insensitive to substitutions at carbon, and substituents greatly influence the potential in the environment of the molecule. The implications of the results for the chemical behavior of sulfine derivates are briefly discussed and compared with experimental data. Sulfines, which are defined as the S-monoxides of thiocarbonyl derivates, have attracted considerable at­ tention in the recent literature. Although the first sulfine was reported as early as 1923,' more general synthetic routes to this class of compounds were developed some 40 years later. Dehydrohalogenation of sulfinyl chlorides2-4 and oxidation of thiocarbonyl containing substrates such as aromatic thioketones,5 thioacid chlorides,6,7 dithiocarboxylic esters,8,9 and non-enethiolizable aliphatic thiones10 can be utilized to prepare a wide variety of substituted sulfines. The parent sulfine, H2C=S=0, has recently been generated by flash vacuum pyrolysis of thietane S-oxide and 1,3-dithietane I-oxide.11,12 The bent structure of these heterocumulenes has been well established by dipole moment measurements,9,13,14 NMR spectroscopy,8,9,15 X-ray analysis,16 and by the isolation of stable geometrical isomers,7-9,13 of sulfines of the type XYC=S=0 with X ^ Y . The chemical behavior is presently under active investigation. Cycloaddition reactions were observed with dienes17 and 1,3-dipoles.18 The course of the reaction with nucleophilic species depends on the nature of the reagent as well as on the substituents attached to the sulfine carbon atom: For instance, alkyl lithium reacts exclusively at the sulfine sulfur atom to give alkyl sulfoxides,19 chlorosulfines show a displacement of the chlorine upon reaction with aniline,13 p-toluenethiolate,7 potassium thiocyanate,7 and p-toluenesulfinate,20 while aryl arylthiosulfines7 react with arenethiolates primarily at the sulfine sulfur atom. Initial attack on that atom was also observed during the reaction of aryl arylsulfonyl sulfines with p-toluenesulfinate,20 cyanide,20 and hydroxide ions.20 Electrophilic reagents preferably react at the sulfine oxygen atom. The acid-catalyzed hydrolysis21 of sulfines is assumed to proceed via initial oxygen protonation. Electrophilic oxygen alkylation has recently been accomplished with triethyloxonium tetrafluoroborate.22 Theoretical calculations of sulfines reported thus far only deal with the parent system (simple Hiickel,5b CNDO/2,23,24 ab initio.12 25) The aim of the present study is to gain insight in the influence of substituents at the sulfine carbon atom on the charge distribution and some molecular properties, and also to compare the results of ab initio calculations with those obtained by less sophisticated methods. To this end, a set of nine simple halogen substituted sulfines was studied. The substituents on the carbon atom are all possible combinations of H, F and Cl atoms, viz. H2, F2, Cl2, cis and trans HF, HC1 and FC1. Molecular potential maps were computed in order to shed some light on the factors governing reactions of sulfines with nucleophiles and electrophiles. COMPUTATIONAL ASPECTS The wave functions of the nine molecules mentioned above were calculated using Roothaan’s MO-LCAO-SCF method,26 both ab initio and by means of the semi-empirical INDO method (Intermediate Neglect of Differential Overlap27-29). If the results of the INDO calculations satisfactorily match those obtained by the ab initio method, one could use this faster method also for calculating wave functions for larger sulfines or related com­ pounds. For the ab initio calculations the IBMOL5A program by Clementi et ai was used;30 the INDO program was written by Van der Lugt.29 Information on the ab initio Gaussian Type Orbital (GTO) bases is presented in Table 1. The INDO calculations used a minimal Slater Type Orbital (STO) basis, with exponents taken from Clementi and Raimondi.33 The ionisation potentials, also required as input to the INDO program, were calculated from spectral data.34 From the wave functions several interesting properties could be calculated. The ab initio wave functions were used for population analysis and for dipole moment and molecular potentials calculations. From the INDO wave functions atomic populations and dipole moments were computed. Also the electronic spectra were calculated, by adding a singly excited Configuration Interaction (Cl) to the INDO calculations. For the smaller molecules all possible single excitations were considered; for the others only the 60 single excitations lowest in energy were taken into account. For the ab initio population analyses and dipole moment calculations a molecular properties program, written by Van Duijneveldt et al. 3 3 was applied. The molecular potentials