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13 C NMR study of the overall and internal motions of a semi‐rigid hydrocarbon
Author(s) -
Gillies D. G.,
Matthews S. J.,
Sutcliffe L. H.
Publication year - 1990
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.1260280215
Subject(s) - chemistry , relaxation (psychology) , spin–lattice relaxation , spectral line , amplitude , nuclear overhauser effect , dilution , hydrocarbon , nuclear magnetic resonance , analytical chemistry (journal) , nmr spectra database , internal rotation , rotational correlation time , nuclear magnetic resonance spectroscopy , molecular physics , stereochemistry , molecule , thermodynamics , physics , organic chemistry , optics , nuclear quadrupole resonance , quantum mechanics , social psychology , psychology , mechanical engineering , engineering
An extensive investigation has been made of the 13 C NMR relaxation parameters of 2,4‐dicyclohexyl‐2‐methylpentane neat and in solution. Spin‐lattice relaxation times and nuclear Overhauser enhancements were measured as a function of temperature, concentration and radiofrequency. The results for all the carbons, except the methyls, can be interpreted by using a reduced spectral density which suggests that there is an isotropically rotating semi‐rigid backbone structure whose internal librations and vibrations reduce the amplitude of the spectral density. However, interpretation of the methyl group data required the addition of a discrete correlation time characteristic of the internal motion about a C 3 axis. From dilution studies, the validity of using the two‐correlation time spectral density with S 2 = 0 when the rate of overall motion approaches that of the internal motion was established, for the first time.