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|Type:||Artigo de periódico|
|Title:||Difference between (2)J(C2H3) and (2)J(C3H2) spin-spin couplings in heterocyclic five- and six-membered rings as a probe for studying sigma-ring currents: a quantum chemical analysist|
dos Santos, FP
|Abstract:||Adequate analyses of canonical molecular orbitals (CMOs) can provide rather detailed information on the importance of different sigma-Fermi contact (FC) coupling pathways (FC term transmitted through the sigma-skeleton). Knowledge of the spatial distribution of CMOs is obtained by expanding them in terms of natural bond orbitals (NBOs). Their relative importance for transmitting the sigma-FC contribution to a given spin-spin coupling constants (SSCCs) is estimated by resorting to the expression of the FC term given by the polarisation propagator formalism. In this way, it is possible to classify the effects affecting such couplings in two different ways: delocalisation interactions taking place in the neighbourhood of the coupling nuclei and 'round the ring' effects. The latter, associated with sigma-ring currents, are observed to yield significant differences between the FC terms of (2)J(C2H3) and (2)J(C3H2) SSCCs which, consequently, are taken as probes to gauge the differences in sigma-ring currents for the five-membered rings (furan, thiophene, selenophene and pyrrol) and also for the six-membered rings (benzene, pyridine, protonated pyridine and N-oxide pyridine) used in the present study. Copyright (C) 2010 John Wiley & Sons, Ltd.|
|Subject:||geminal coupling constant difference|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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