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|Type:||Artigo de periódico|
|Title:||Conformational And Electronic Interaction Studies Of α-substituted Carbonyl Compounds. Xiv. α-(arylsulfonyl)-p-substituted Acetophenones|
|Abstract:||The VCO IR analysis of α-(p-phenylsulfonyl)-p-substituted acetophenones X-øC(O)CH2S(O)2ø-Y 1-8, being X and Y = NO2, H and OMe substituents, supported by Molecular Mechanics data of the α-methylsulfonylacetophenone (model compound), indicates the existence of the cis/gauche rotational isomerism. The less polar gauche2 rotamer is the more stable (conc. ≅ 90%) and the more polar cis rotamer is the less stable one along the series. Compounds 4 (X = Y = H) and 3 (X = H, Y = OMe) present another less stable and rather polar gauche1 rotamer. The almost constant carbonyl gauche2 shifts (Δvg2) together with the quasi-invariability of the cis/gauche ratios, when X varies and Y is fixed, indicates a very nearly constant summing up of π*CO/σC-SO2 and πCO/σ*C-SO2 orbital interactions. The progressive stabilization of the gauche2 rotamer when X is fixed and Y changes from NO2 to OMe substituents, along with the parallel decrease of the positive sulfonyl asymmetric frequency shifts (ΔvSO2g2) is discussed in terms of the progressive contribution of the O(SO2) → C(CO) electrostatic and charge transfer interactions. Additional support for the proposed interactions is given by the large NAE mean value tor the α-methylene carbon chemical shifts together with the upfield shift of the β-ketosulfones mean carbonyl carbon chemical shifts in relation to that of the β-ketosulfoxides.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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