General Review of Proton Magnetic Resonance

Abstract

Publisher Summary This chapter presents a general review of proton magnetic resonance (PMR). The chapter explores two significant papers on the theory and correlation of coupling constants that have used a theoretical valence bond description of contact nuclear spin-spin coupling. Perturbation theory and Penney-Dirac bond orders are used to obtain a simple form for the average energy valence-bond model of the contact contribution to proton coupling constants. For the most common molecular systems, in which there are only small deviations from a localized bond description, the vicinal and long-range coupling constants are expressed in terms of the bond orders for four-electron fragments. Geminal, vicinal and long-range couplings, and couplings in aromatic and heteroaromatic systems are discussed in the chapter. A linear relationship between the proton chemical shifts for substituted aliphatic derivatives and the positive charge density on hydrogen, as determined by a M.O.-L.C.A.O. method, is obtained. The procedure, whereby the magnitude of the magnetic anisotropy of bonds is calculated from a study of relative chemical shifts, has been employed to estimate the magnetic anisotropy of the acetylenic, nitrile, and isonitrile triple bonds. Conformational analysis now ranks amongst the most important branches of organic stereochemistry, and the derivation of information about the conformation and configuration of molecules from coupling constant and chemical shift data is well documented in this chapter. The recent advent of high field superconducting magnet spectrometers has greatly increased the number of studies of biological systems that have employed NMR spectroscopy.