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Deuterium Isotope Effects on 13 C Chemical Shifts in cis ‐Stilbene
Author(s) -
Meić Z.,
Novak P.,
VikićTopić D.,
Smrećki V.
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(199601)34:1<36::aid-omr833>3.0.co;2-9
Subject(s) - chemistry , isotopomers , kinetic isotope effect , deuterium , steric effects , molecule , dihedral angle , isotope , deuterium nmr , chemical shift , crystallography , stereochemistry , hydrogen bond , computational chemistry , carbon 13 nmr , organic chemistry , physics , quantum mechanics
Abstract Over 100 isotope effects on 13 C chemical shifts were determined in a series of deuteriated cis ‐stilbene isotopomers. The magnitude and sign of these effects depend on the position and the number of deuterium atoms in the molecule. The variations in two‐ and three‐bond effects were rationalized by steric interactions between the phenyl ring and the olefinic group. The six‐bond effects in cis ‐stilbene isotopomers are related to the molecular Ph—CξC dihedral angle, as in other binuclear aromatic molecules. In [ para ‐ 2 H]‐ cis ‐stilbene the isotope effect over ten bonds was observed, amounting to 2.0 ppb. In mono‐ and dideuterio‐ cis ‐stilbenes, effects over up to three bonds from the site of the deuteriation have a positive sign and decrease monotonously in magnitude. In contrast, effects through more than three bonds generally show an alternation in sign and oscillations in magnitude. In polydeuteriated cis ‐stilbenes, changes in sign and magnitude are governed by the additivity rule, which reproduces the observed values of isotope effects within a few percent.