Proton two-dimensional multiple pulse NMR experiments on the nematic liquid crystal MBBA

Abstract

Two types of 1H two-dimensional (2D) multiple pulse experiments were performed on the nematic liquid crystal MBBA (4'-methoxybenzylidene-4-n-butylaniline). In one of them, a multiple pulse sequence is applied in the t 2 dimension to separate the 1H–1H dipolar spectra by the chemical shifts. The other type is a 2D exchange NMR experiment with multiple pulse sequences in both t 1 and t 2 periods by which spin diffusion between protons with different chemical shift values is observed through cross-peaks. The data were analysed by an additive potential model. The dipolar spectra obtained by the first experiment were found to be sensitive to the twist angles of the two phenyl rings from the -CH=N- plane. The twist angles were determined to be 33° for the N-side phenyl ring and 20° for the C-side phenyl ring.