Chapter 2 - Two-Dimensional Higher Quantum Correlation and Resolved Techniques for the Analyses of Complex 1H NMR Spectra of Scalar-Coupled Spins

Abstract

Abstract The number of permitted single quantum (SQ) transitions in the 1H NMR spectra of scalar-coupled spins increases rapidly with the increase in the number of interacting spins, thereby posing a challenge for their analyses. The numerous two-dimensional methodologies are available in the knowledge bank of NMR for the determination of spectral parameters and to obtain information on the molecular structure and conformation. The indirect detection of forbidden higher quantum NMR transitions, that is, other than those allowed by the normal selection rules for the detection of SQ frequencies, is one of the significant steps in this direction. The detection of higher quantum transitions of coupled spin 1/2 nuclei has been extensively employed for the study of molecules oriented in strong and weak aligning media, not only to simplify the analyses of complex NMR spectra but also to determine the molecular geometries. In this chapter, we discuss our recent studies on the development and applications of higher quantum correlation and resolved techniques for the analyses of complex 1H NMR spectra of scalar-coupled spins. The behaviour of magnetization in the spin-selected and non-selected higher quantum is discussed using both product operator and polarization operator approaches for a weakly coupled AMX spin system. Subsequently, applications of these methodologies for the analyses of complex 1H NMR spectra have been discussed with specific examples.