Monochalcogenocarboxylic acid

Li et studied the monochalcogenocarboxylic acids CH3COXH with X being S, Se, or Te (Fig. 10) both in vacuum and in a THF (tetrahydrofuran) solution. They used the polarizable continuum model and calculated the electronic properties of the solute by using Hartree-Fock calculations with a second order Moller-Plesset treatment of correlation effects. They compared the enol and the keto forms and calculated also the transition state between the two. Finally, they considered both... 

Fig. 10 Schematic representation of (left part) the enol and (right part) the keto forms of monochalcogenocarboxylic acids CH3COXH with X being S, Se, or Te. Open circles, closed circles, closed triangles, and closed squares mark hydrogen, carbon, oxygen, and the chalcogen atom, respectively.

Table 20 The relative total energies in kJ/mol for systems containing n CH3OCH3 molecules plus either the keto or the enol form of the monochalcogenocarboxylic acids of Fig. 10. TS shows the results for the transition state between the two forms. The phase marks whether gas phase or a THF (tetrahydrofuran) solution is considered. All results are from ref 72... 

As shown in Scheme 1, there are 15 kinds of chalcogenocarboxylic acid. There are six monochalcogenocarboxylic acids, that have oxygen and chalco-gen atoms (A), as well as their tautomers (A ). There are also the dichalcogeno-carboxylic acids (B and C), while the dichalcogenocarboxylic acids with two different chalcogen atoms (of which there are three kinds, B) also possess tautomers (B ). 

Table 3 Selected bond distances of main-group-element compounds of monochalcogenocarboxylic acids...

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