Effect of sulfur oxidation on the transmission mechanism of 4-J(H,H) NMR coupling constants in 1,3-dithiene

G. F. GAUZE, E. A. BASSO, R. H. CONTRERAS, C. F. TORMENA

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington DC; Año: 2009 vol. 113 p. 9874 - 9880

1089-5639

A qualitative approach to analyze the electronic origin of substituent effects on the paramagnetic part of chemical shifts is described and applied to few model systems, where its potentiality can be appreciated. The formulation of this approach is based on the following grounds. The influence of different inter- or intramolecular interactions on a second-order property can be qualitatively predicted if it can be known howthey affect the main virtual excitations entering into that second-order property. A set of consistent approximations are introduced in order to analyze the behavior of occupied and virtual orbitals that define some experimental trends of magnetic shielding constants. This approach is applied first to study the electronic origin of methyl-alfa substituent effects on both 15N and 17O chemical shifts, and afterward it is applied to a couple of examples of long-range substituent effects originated in charge transfer interactions such as the conjugative effect in aromatic compounds and ó-hyperconjugative interactions in saturated multicyclic compounds-alfa substituent effects on both 15N and 17O chemical shifts, and afterward it is applied to a couple of examples of long-range substituent effects originated in charge transfer interactions such as the conjugative effect in aromatic compounds and ó-hyperconjugative interactions in saturated multicyclic compounds