Simplification of19F NMR Spectra of Liquid Crystalline Samples by Multiple-Pulse COSY Experiments

✍ Scribed by Philippe Lesot; James W. Emsley; Jean-Michel Ouvrard; Eirian Curzon

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 163 KB
• Volume: 133
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.1998.1452

✦ Synopsis

A general method is presented of converting second-order fluorine-19 spectra of liquid crystalline samples into first-order spectra. This is achieved by recording a 19 F COSY spectrum with a multiple pulse dipolar reducing sequence (MPS) operating in the t 1 period, leading to a F 1 projection which is first order. The method is illustrated by recording spectra on a sample of 1,3-dichloro-4fluorobenzene dissolved in the nematic solvent ZLI 1167. Experiments have been done in which the MPS is either the MREV-8 or Flip-Flop-16 sequence. The first-order F 1 projections are analyzed to give reduced total 1 H-19 F couplings, K CS T ij HF and the reduction factors, K CS , are obtained by comparison with the T ij HF available from an analysis of the ordinary 1D spectrum. The reduction factors are compared with values predicted by average Hamiltonian theory (AHT). The reasons for the differences found between observed and predicted values of K CS have been investigated by performing numerical simulations of the 2D MPS COSY experiments.