Additivity of Proton Magnetic Resonance Solvent Shifts in the Azine Series

Publisher Website
Google Scholar
Abstract
Shifts induced by aromatic solvents upon resonances of polar solutes are observed to be additive. Incremental solvent shifts can be ascribed to a proton which has a given relationship with a polar substituent or a heteroatom. There is a dispute as to whether this additivity is merely a consequence of the additivity of substituent effects in any solvent or whether it is an independent phenomenon. Heterocyclic molecules for which additivity in the first sense does not hold are studied. The results are also discussed with respect to the nature of the interaction between the polar solute and the aromatic solvent. It is pointed out that the existing models do not account satisfactorily for both the additive behavior and the observed increments. These empirically derived quantities are quite successful in relating the solvent shifts of a number of compounds; for the ring protons of methyl and polymethyl pyridines, pyridazines, pyrimidines, and pyrazines, the carbon tetrachloride to benzene incremental shifts are −0.07 (ortho‐N), 0.44 (meta‐N), 0.56 (para‐N), and −0.11 ppm per methyl group irrespective of its substitution site.

This publication has 19 references indexed in Scilit: