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Inhibition and enhancement of resonance as studied by 13 C nuclear magnetic resonance spectroscopy
Author(s) -
Kitching William,
Jonge Ian De,
Adcock William,
Abeywickrema Anil N.
Publication year - 1980
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270140615
Subject(s) - steric effects , substituent , chemical shift , resonance (particle physics) , chemistry , planarity testing , nuclear magnetic resonance spectroscopy , nuclear magnetic resonance , spectroscopy , crystallography , stereochemistry , atomic physics , physics , quantum mechanics
13 C chemical shifts are reported for a series of 2‐substituted 1,3‐dimethylbenzenes: comparisons of these values with those for the corresponding monosubstituted benzenes reveal, in some cases, large differences in the para ‐carbon substituent chemical shifts, which are attributable to steric hindrance of resonance. The questions of steric enhancement of resonance, and methoxy group conformation in certain anisoles are also studied by the 13 C NMR technique. Studies of selected 2‐substituted fluorenes are also reported, and substituent chemical shifts at carbon‐7 (traversing eight bonds) of greater than 2ppm are observed. These effects are consistently greater than those reported for the corresponding biphenyl compounds, and are associated with planarity‐enforced enhancement of resonance.