Measurement of Interproton, Nuclear Spin Dipolar Couplings in Liquid Crystalline Samples by Combining Variable Angle Sample Spinning, Isotope Dilution, and Deuterium Decoupling
✍ Scribed by E. Ciampi; G. De Luca; J.W. Emsley
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 138 KB
- Volume
- 129
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
The proton NMR spectra of liquid crystalline samples can be but it has not been used to study a mesogenic molecule since simplified by selective, partial deuteration followed by deuterium these are not easily fully deuterated catalytically (5). The decoupling. This leaves strong peaks from the protons at the unmethod demonstrated here combines variable angle sample deuterated sites, but also weak resonances from the coupling of spinning to control the ratio of chemical shifts to dipolar these protons to those at low abundance (2% in the present case) couplings, with specific deuteration of one part of a molecule at the deuterated sites. The weak resonances can be separated with random deuteration of another, a combination which is from the strong by recording spectra while spinning the sample more easily achieved for compounds with different kinds of at a series of angles to the magnetic field. ᭧ 1997 Academic Press molecular subgroups, such as mesogens.
The sample used to demonstrate the technique is 4-npentyl-4-cyanobiphenyl (5CB)-d 15 which contains 98% of Dipolar couplings, D ij , between nuclei in molecules which isotopomer 1 with the pattern of deuteration are in liquid crystalline phases provide the key to unlocking the details of structure, orientational order, and conformational distributions (1). There is, however, a fundamental problem in obtaining dipolar couplings in that their presence often renders a NMR spectrum so complex as to be unresolved. This is particularly true for proton spectra of mesogenic molecules, or of solutes of similar structural complexity, and the standard approach is to simplify the spectra by replacing some of the protons by deuterium, followed by deuterium decoupling (2, 3).