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2 Polish Journal of Chemistry

2 1999

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Quantum chemical calculations on S-centered 1,3-dipoles : 2. Reactivity of thiocarbonyl S-imides in perycyclic reactions

Mlostoń G., Fabian J.

Polish Journal of Chemistry

1999

vol. 73 nr 4

683-692

Results of high level quantum chemical calculations on thiocarbonyl S-imides 1 are reported. The reactivity of thioformaldehyde S-imide (1a) (CH2S+NH-) in pericyclic reactions was calculated by density functional theory using gradient corrected functionals 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 at correlated levels of theory, such as MP2, QCISD(T) G1 and G2(MP2), were also performed. The predicted reactivity of the parent compound is compared with those of some closely related ylides (S-centered 1,3-dipoles), such as thioformaldehyde S-methylide (2a), thioformaldehyde S- oxide (3a) and thioformaldehyde S-sulfide (4a). To show the effect of substitution on structure and reactivity a series of acyclic and cyclic substituted thiocarbonyl S-imides 1b-k was calculated. The 1,3-electrocyclic ring closure of 1a to form thiaziridines 5 is predicted to be exothermic process by about 10 kcal/mol with activation energies of about 30 kcal/mol. The calculated reaction energies are considerably affected by higher angular momentum polarization functions, such as f-functions. In the case of some substituted thiocarbonyl S-imides, such as thiotropone S-imide (1i) and thiofluorenone S-imide (1j), the exothermicity of the ring closure reaction is lower than that of the parent compound. The concerted prototype [3+2]-cycloaddition of 1a with ethylene is strongly exothermic (about 50 kcal/mol) with the activation energy of about 20 kcal/mol. The energetics of both types of the pericyclic reactions of 1a appears closely related to that of 4a but differs more strongly from that of 3a. The contemporary knowledge on thiocarbonyl S-imides 1 is reviewed and discussed in conjunction with theoretical results.

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.