High resolution solution state double quantum spectroscopy of two-spin-1 AX systems and mimics

Abstract

Double quantum spectroscopy (DQS) of the two-spin-1 AX system in the liquid state is investigated theoretically. The two kinds of double quantum coherence (DQC) that arise are studied and expressions are given for their evolution under weak scalar coupling and chemical shifts. A one-dimensional double quantum J (DQJ) filter sequence for the separation of the two kinds of DQC is introduced. Analytical expressions are given for the spin response to the general two-dimensional DQS sequence, for an arbitrary reconversion pulse flip angle β. A detailed investigation of the coherence transfer (CT) amplitudes has been carried out by computer simulation of CT amplitudes as a function of β. The differences in the behaviour of CT amplitudes of one-spin DQC, 'outer' and 'central' components of two-spin DQCs are discussed. Optimum flip angles for maximizing sensitivity of N-type, P-type and pure phase double quantum spectra of this system are deduced. The detailed predictions are borne out by recently published experimental work on two-spin-1 AX systems, as well as our studies on a mimic arrangement, viz., a spin-½A₂X₂ system.