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|Type:||Artigo de periódico|
|Title:||On the (4)J(HH) long-range coupling in 2-bromocyclohexanone: conformational insights|
|Abstract:||2-Bromocyclohexanone is a model compound in which a (4)J(H2,H6) coupling constant is observed, whereas the corresponding (4)J(H2,H4) is absent. The observed long-range coupling is not only a result of the known W-type coupling, in the axial conformation, but also because of the less usual diaxial spin-spin coupling in the equatorial conformer. The carbonyl group plays a determining role in describing the coupling pathway, as concluded by natural bond orbital (NBO) analysis; although the sigma(C2-H2) -> sigma(*) (C1(O)-C6) and sigma(C6-H6) -> sigma(*) (C1(O)-C2) interactions in the axial conformer contribute for transmitting the spin information associated with the W-type coupling, the strong sigma(C2-H2) -> pi(*) (C=0) and sigma(C6-H6) -> pi(*) (C=0) hyperconjugations in the equatorial conformer define an enhanced coupling pathway for (4)J(H2,H6), despite the inhibition of this coupling because of n(o) -> sigma(*) (C(O)-C) interaction and the large carbonyl angle. These findings provide the experimental evidence that orbital interactions contribute for the conformational isomerism of 2-bromocyclohexanone. Copyright (c) 2008 John Wiley & Sons, Ltd.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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