RESEARCH NOTE The effect of acquisition delay on single- and multiple-quantum proton NMR spectra of liquid crystals

Abstract

Proton NMR spectra of bulk liquid crystals show broad peaks with very little fine structure. Using a simple technique called acquisition delay, a huge number of sharp peaks can be observed. In this method, an appropriate delay time is inserted after the radio frequency pulse is applied, before the receiver of the spectrometer is turned on; alternatively, the initial part of the free induction decay can be discarded before Fourier transform of the data is carried out. The feature of the spectrum with acquisition delay is strongly dependent on the delay time. Similar characteristics are also observed for multiple-quantum proton spectra, when a delay time is inserted after the second π/2 pulse in the evolution period. Therefore, although the multiple-quantum spectra of a liquid crystal are as broad as its conventional single-quantum spectrum, the use of acquisition delay also filters out the broad components in the multiple-quantum spectra to show fine structures.