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1 H and 13 C NMR study of hindered rotation in N 1 , N 1 ‐dimethyl‐ N 2 ‐substituted phenylacetamidines
Author(s) -
Wawer Iwona
Publication year - 1988
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/mrc.1260260713
Subject(s) - chemistry , steric effects , planarity testing , ring (chemistry) , nmr spectra database , substituent , moiety , stereochemistry , carbon 13 nmr , crystallography , spectral line , medicinal chemistry , organic chemistry , physics , astronomy
Barriers to rotation about the partial double CN 1 bond were determined from line shape analysis of 1 H and 13 C dynamic NMR spectra of N 1 , N 1 ‐dimethyl‐ N 2 ‐substituted phenylacetamidines with twelve different substituents on the phenyl ring. The values of Δ G Tc ≠are 51.2–58.7 kJ mol −1 and the correlation with Hammett's σ values indicates an important contribution from the substituent effects to the barrier height. The decrease of the rotational barrier of approximately 10 kJ mol −1 in acetamidines in comparison with the respective formamidines is probably mainly due to a steric interaction of the CCH 3 group with aromatic protons; this leads to non‐planarity and a decrease of the conjugation of the aromatic ring with the acetamidine moiety.