13C NMR study of the overall and internal motions of a semi-rigid hydrocarbon

✍ Scribed by D. G. Gillies; S. J. Matthews; L. H. Sutcliffe

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 440 KB
• Volume: 28
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260280215

✦ Synopsis

Abstract

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.