1. Purpose

If liquid crystals are used as NMR solvents, dissolved molecules no longer tumble isotropically but can be partially oriented along one axis of the liquid-crystal phase. Effects of chemical shift anisotropy, of the dipolar coupling D, and of the anisotropy of J become visible; these are normally not present in an isotropic solution. Therefore, from detailed spectral analysis of such spectra, relative internuclear distances, the absolute sign of spin–spin coupling constants, and data about molecular reorientation can be obtained. Currently, a new field of NMR research is evolving, where liquid crystals are used for partial alignment [7]. As an example, we show in this experiment the spectrum of benzene in a nematic phase, which gives a strikingly complex spectrum for this simple symmetrical molecule.

2. Literature

A. Saupe, G. Englert, Phys. Rev. Lett. 1963, 11, 462–464.
J. W. Emsley, J. C. Lindon, NMR Spectroscopy Using Liquid Crystal Solvents, Pergamon, Oxford, 1975.
C. L. Khetrapal, A. C. Kunwar, A. S. Tracey, P. Diehl, NMR Basic Principles and Progress, 1975, 9, 1–85.
A. D. Buckingham, K. A. McLauchlan, Prog. NMR Spectrosc. 1967, 2, 63–109.
C. L. Khetrapal, A. C. Kunwar, Adv. NMR Spectrosc. 1977, 9, 301–422.
J. Kaski, J. Vaara, J. Jokisaari, J. Am. Chem. Soc. 1996, 118, 8879–8886.
E. de Alba, N. Tjandra, Prog. NMR Spectrosc. 2002, 40, 175–197.

3. Pulse Scheme and Phase Cycle

Standard proton pulse sequence and phase cycle

4. Acquisition

Time requirement: 15 min

Sample: 0.05 ml benzene in 0.5 ml (4-n-heptylcyclohexyl)-p-cyanobenzene (Merck Licrystal^® PCH7)