INTERCONVERSION KINETICS AND ORDERING OF CIS-DECALIN IN LIQUID-CRYSTALLINE SOLVENTS BY 1D AND 2D DEUTERIUM NMR

The deuterium NMR spectrum of perdeuterated c/r-decalin in liquid-crystalline solvents is studied over the temperature range-5 to ~ 160 °C. The spectrum exhibits dynamic features due to the interconversion process of the cis-decalin molecules. For the quantitative analysis of the spectra, complete peak assignment is performed (i) by using selectively deuterated cis-decalin in the β-position, (ii) by using 2D exchange spectroscopy at low temperatures, and (iii) by fitting the observed spectrum with that expected from the minimum energy structure derived from molecular mechanics calculations. The analysis also provides all components of the ordering matrix of cis-decalin in the nematic solvents used. It is found that the orientations of the principal directions of this ordering matrix in the molecular frame is temperature dependent, apparently due to solvation effects. A quantitative analysis is made of the spectrum line shape over the whole experimental temperature range in terms of the interconversion reaction of cis-decalin, yielding the rate equation k = 3.9 ⨯ 1014 exp(-15.5/RT), where R is in kcal mol-1 K-1. The results are compared with those previously obtained by 13C NMR. © 1990, American Chemical Society. All rights reserved.