Theoretical study of the internal elimination of xanthates using ONIOM additivity and pseudopotentials / Estudo teorico do mecanismo de eliminação interna de xantatos usando o metodo aditivo de energia atraves de ONIOM com pseudopotencial

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The gas-phase internal elimination (Ei) reaction of xanthates and the decomposition of xanthic acid have been investigated using ONIOM Additivity Expression and Pseudopotential, ONIOM[CCSD(T)/CEP-311 (2d,f):MP2/CEP-31G//MP2/CEP-31G]. The higest leveI representation was calculated by means of CCSD(T)/CEP-31G and electronics and sterics effects by MP2/CEP-31G. The Ei reaction of [CH3CH2SC(=S)(OCH3)]- ethyl xanthate was used as a model, using CCSD(T)/CEP-311(2d,f)j//MP2/CEP-31G. This mechanism involves a six-membered ring transition state structure in two analogue processes. In the first, the H-b is transferred to S, via TS(1) while in th second, the H-b is transferred to O, via TS(2). The reaction is endothermic (25,1 kcal/mol) and the activation energies for transition states (1) e (2) are 47,2 and 67,2 kcal/mol, respectively. The TS(1) activation energy value closely matches the value found in the literature, when using CCSD(T)/aug-cc-pVDZ. The Ei reaction of (C6H5)CH2(C6H5)CHSC(=S)(OCH3) is exothermic (-46,8 kcal/mol) and the activation energies for transition states (1) e (2) are 34,7 and 49,2 kcal/mol, respectively. This stabilization is attributed to the conjugation of the double bonds in the phenyl group: with the p bond formed in the Stilbene compound (stilbenes are known to possess important pharmacological properties).

ASSUNTO(S)

metodo aditivo de energia pseudopotential xantatos oniom additivity expression pseudopotencial xanthates

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