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Structure and Properties of 1,2-Dithiolylium-4-methide, 1,2-Dithiolylium-4-olate and 1,2-Dithiolylium-4-thiolate - A MO Study at the HF- and post-HF-level
 
J. Phys. Org. Chem. 8 (1995), 536
M. Mann and J. Fabian

 
Abstract:
The molecular and electronic structures of the cyclic 1,2-dithiolium ylides (2) and their acyclic dithiocarbonyl valence isomers (4) have been studied with ab initio methods. All molecular structures were fully optimized at the R(U)HF/6-31G* and R(U)MP2/6-31G* levels of theory. The results of the restricted and unrestricted HARTREE-FOCK (HF) calculations are less reliable since the RHF wavefunctions of the cyclic compounds proved to be singlet/triplet unstable. A marked ground state energy depression occurs on passing from restricted to unrestricted HF methods. The title compounds are of diradicaloid nature and belong to the non-classical class of structures. The heterocycles are planar and display C2v- symmetry while the cisoid open chain dithiocarbonyl isomers are slightly distorted (C2- symmetry). According to the calculated bond lengths and charge distributions the title compounds are in fact more or less zwitterionic. The thiolate is the most polar compound of this series. According to RMP2 calculations, the thiolate (2, X=S) and olate (2, X=O) should exist in singlet ground rather than in triplet state. However, in these cases the isomeric acyclic compounds are predicted to be almost isoenergetic with the cyclic ones. Since the cyclic ylides have higher dipole moments than the acyclic dithiocarbonyls the ylides will gain stability in polar solvents. However, the continuum quantum chemical model used in estimating the solvent effect does not favor the ring compounds sufficiently enough to exclude valence isomerization between the ring closed and ring open compounds.

 
 

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TU Dresden
Fakultät Mathematik und
Naturwissenschaften
Fachrichtung Chemie
und Lebensmittelchemie
01062 Dresden

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TU Dresden
Fakultät Mathematik und
Naturwissenschaften
Fachrichtung Chemie
und Lebensmittelchemie
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01069 Dresden

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