Solvent-induced changes in ²J(H, F) for fluoroform via van der Waals interactions. Non-contact contributions to spin–spin coupling constants involving a proton?

Abstract

. Can. J. Chem. 57, 1877 (1979). The spin-spin coupling between the proton and the fluorine nuclei, 'J, in fluoroform varies by 1% in a range of solvents. It is argued that 'J decreases algebraically as the van der Waals solute-solvent interactions increase in magnitude. Such a decrease is also observed for coupling constants which likely contain a substantial positive orbital contribution. If the van der Waals interactions perturb the spin-orbital term in J , then 'J in fluoroform may well contain orbital contributions, as recently calculated for 'J in methyl fluoride. In that event, the large discrepancies between observed 'J(H,F) values and those calculated by semiempirical theories of the contact term may be partially attributed to the neglect of orbital terms.TED SCHAEFER, HAROLD M. HUTTON et SALMAN R. SALMAN. Can. J. Chem. 57. 1877(1979). Le couplage spin-spin entre le proton et le fluor, 'J, du fluoroforme varie par 1% dans divers solvants. On suggere que 'J diminue d'une f a~o n algebrique au fur et a mesure d'une augmentation des interactions de van der Waals solute-solvant. On observe aussi une telle diminution des constantes de couplage qui contiennent probablement une contribution orbitalaire positive importante. Si les interactions de van der Waals perturbent le terme orbltalaire du spin de J , il est possible que la valeur 'J du fluoroforme puisse contenir des contributions orbitalaires semblables a celles calculCes recemment pour le ' J du fluorure de methyle. Alors, on pourrait attribuer en partie les grandes differences observees entre les valeurs de 'J(H,F) obsemtes et calculees par des theories semi-empiriques au fait que des termes orbitalaires ont etC omis.[Traduit par le journal]

Inclusion of hydrogen p orbitals in the semiempirical calculation of NMR parameters. III: INDO CHF calculations of orbital and dipolar contributions to spin–spin coupling constants involving protons

“…Recently, Schaefer et al [33] found experimental evidences that would indicate the presence of interaction mechanisms of the noncontact types in couplings involving protons. Therefore, at present, it seems to be of some importance to study more thoroughly these mechanisms, and in particular, to revise the validity of the McConnell approximation 1231.…”