Pulse sequences utilizing the correlated motion of coupled heteronuclei in the transverse plane of the doubly rotating frame

Abstract

In terms of the Heisenberg vector model, heteronuclei undergo a correlated motion via scalar coupling when both have their spins simultaneously in the transverse plane of the doubly rotating reference frame. Several pulse sequences are described in terms of 1H/ 13C systems. A theoretical analysis of the correlated motions is given for methine (CH), methylene (CH 2), and methyl (CH 3) groups for the situation when the 'H magnetization vectors are initially placed in the transverse plane of the doubly rotating frame and are allowed to precess freely for (2 J) −1 sec, where J is the single-bond 1H- 13C coupling constant, prior to the carbon polarization transfer vectors being placed in the transverse plane. The analysis is confirmed experimentally using two-dimensional NMR and the usefulness of the sequences for two-dimensional NMR is assessed. The family of sequences is completed with a theoretical study of sequences which employ polarization transfer in addition to the correlated motion. Experimental verification for the one-dimensional use of these sequences, the exclusive polarization transfer sequence (EPT), in editing 13C spectra is given. Reverse EPT, the inverse of EPT, is also described and is shown to be useful for editing 1H spectra. While it is pointed out that we expect there to be a correspondence between correlated motion and Schroedinger picture multiple-quantum coherence, the details of this correspondence are not explored.