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1 1999

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Quantum chemical calculations on S-centered 1,3-dipoles : 1. Molecular and electronic structures of thiocarbonyl S-imides

Fabian J., Mlostoń G.

Polish Journal of Chemistry

1999

vol. 73 nr 4

669-681

Results of high level quantum chemical calculations on thiocarbonyl S-imides of type 4 are reported. Structure and properties of thioformaldehyde S-imide (4b) (CH2SNH) and its derivatives were calculated by DFT(B3LYP) in conjunction with 6-31+G(d,p) and 6-31+G(3df,3dp) basis sets. For the sake of comparison conventional ab initio quantum chemical calculations were also performed at MP2 and QCISD(T) levels. The calculated geometry and molecular properties of 4b are compared with those of closely related ylidic structures such as thioformaldehyde S-methylide (1, R1-R4 =H), thioformaldehyde S-oxide (2,R1-R2 =H), and thioformaldehyde S-sulfide (3, R1-R2 = H). Differently substituted thiocarbonyl S-imides 4d-i were calculated to show the effect of substitution on their molecular and electronic structure as well as on some physical properties. The parent compound 4b in the molecular ground state is predicted to be most stable in the planar and bent anti-conformation with geometric parameters and electronic characteristics of a predominantly ylidic structure. The IR and UV absorption maxima of 4b were calculated and discussed with respect to the expected structure of this reactive intermediate.