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Influence of a Side‐Chain on Deuterium Isotope Effects in 13 C NMR Spectra of Some Benzene Derivatives
Author(s) -
Novak P.,
VikićTopić D.,
Meić Z.,
GacsBaitz E.
Publication year - 1996
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199608)34:8<610::aid-omr938>3.0.co;2-o
Subject(s) - chemistry , isotopomers , kinetic isotope effect , steric effects , side chain , deuterium , benzene , lone pair , conformational isomerism , toluene , ring (chemistry) , stereochemistry , computational chemistry , molecule , photochemistry , organic chemistry , physics , polymer , quantum mechanics
Deuterium‐induced isotope effects on 13 C chemical shifts were measured in a series of benzene derivatives, viz. toluene, benzoic acid and benzophenone. The effects over two, three and four bonds reflect a dependence on the transmission pathway and the nature of the side‐chain. Steric and inductive influences of side‐chain lone pair electrons located at the β‐position to the phenyl ring account for a lower magnitude and negative sign of some effects in the deuteriated phenyl ring. In monodeuteriated benzophenones isotope effects are transmitted to the second phenyl ring, e.g. in p ‐deuteriobenzophenone over up to nine bonds. Although the carbonyl group allows only a minor conjugation between the phenyl rings, the extent, the magnitude and the sign of isotope effects resemble those in fully conjugated molecules, indicating a similar transmission mechanism. In polydeuteriated isotopomers, the additivity of isotope effects holds for the majority of carbon atoms. However, in few cases significant deviations exist owing to perturbations in hydrogen‐bond dynamics and redistribution of rotamer populations caused by deuteriation. For monodeuteriated isotopomers, a number of 13 C– 2 H coupling constants through one and three bonds are also reported.