Intramolecular electric field effect on a1J(C,H) NMR spin-spin coupling constant. an experimental and theoretical study

Abstract

An experimental study of the effects of intramolecular electric fields on 1J(C,H) coupling constants involving a formyl proton in a series of 5‐X‐salicylaldehydes is reported. The particularly large electric field component along the CcHf bond, calculated for X=NO2 , leads to a measured substituent effect of 7.36 Hz. For other X substituents a linear correlation was found between the calculated substituent electric field component along the Cc—Hf bond and the substituent effect on 1J(Cc ,Hf). To determine if 5‐X substituents affect the intramolecular CO· · ·HO hydrogen bond, NBO analyses were carried out on 5‐NO2 − and 5‐H‐salicylaldehyde, and they were compared with those corresponding to benzaldehyde and phenol. The effects of interactions other than the electrostatic one on 1J(Cc ,Hf) couplings were ruled out. The experimental results are in agreement with theoretical predictions published previously. Copyright © 1999 John Wiley & Sons, Ltd.

Configurational and conformational analysis ofO-vinyl ketoximes by1H and13C NMR spectroscopy

“…Such proximity gives rise to an attractive electrostatic interaction of C-H dipole and lone pair. 24,25 This causes a downfield shift of the H b signal which results in an increase in the υ parameter, an increase in the one-bond 1 J(Cˇ,H b ) coupling constant and, hence, a decrease in the J parameter and an algebraic increase in the 2 J(H a ,H b ) coupling constant. 26,27 The υ parameter for O-vinyl ketoximes 1-8 is increased by ¾0.2 ppm and the J parameter is decreased by ¾1 Hz compared with those in divinyl ethers 13 and 14 having a similar conformational equilibrium.…”

Solvent Effects on Nuclear Magnetic Resonance 2J(C,Hf) and 1J(C,Hf) Spin–Spin Coupling Constants in Acetaldehyde

“…Their main attractive interaction corresponds to an electrostatic effect [45] although in some cases there could also be some charge transfer interaction of type n(O)→(CH)* [2]. For C(sp 3 )H and C(sp 2 )H bonds the electrostatic part of this proximate effect causes an increase in its corresponding 1 J(C,H) coupling [46][47] while the charge transfer contribution causes a decrease in such a coupling [2].…”

Electric Field Effects on 2JHH Spin-Spin Coupling Constants

“…There is both experimental and calculated data on intramolecular electric field effects on proton coupling constants and linear correlations to the electric field caused by the electronegativity difference of nearby substituents reported in reference [36]. One of the first calculations of the gradient of the spin-spin coupling constant with respect to a uniform electric field perturbation ∂J/∂F was presented by the author and Raynes [37] when then available computer resources did not allow detailed investigation at a correlated level of the sign change when going from SCF to MCSCF calculations.…”