Effects of intramolecular interactions on NMR J(13C,1H) spin-spin coupling constants: A DFT-B3LYP calculation and exprimental study

two different types of interactions affecting both 1j(c,h) and longer range nj(c,h) spin-spin coupling constants, ssccs, are studied from a theoretical point of view in model compounds. the study, based on the dft methodology, was supplemented with measurements of several nj(c,h) couplings. the studied interactions are, on the one hand, those of electrostatic origin caused by proximity of either an electronegative atom or of an h atom and a c-h bond on the corresponding 1j(csp2,h) sscc. in agreement with previous observations it was determined that the former interaction yields an increase while the latter a decrease in the corresponding 1j(c,h) sscc. both of these changes are notably shielded by the dielectric effect of the solvent. on the other hand, the influence of the strong negative hyperconjugative interactions that take place in the aldehyde moiety on the corresponding 1j(cc,hf) and 2j(c,hf) ssccs, are studied. these negative hyperconjugative interactions are inhibited by, for instance, the intramolecular hydrogen bond in salicylaldehyde, the dielectric effect of the solvent, or the electrostatic effect of a proximate electronegative atom close to the formyl proton of the hf-cc bond.