Spin-rotation constants, nuclear magnetic resonance chemical shifts

Nuclear magnetic resonance spectroscopy has been widely employed in the study of rotational isomer phenomena produced by substituents lacking rotational symmetry. The preferred conformations in solution have been determined by various NMR techniques, essentially (i) analysis of H and C chemical shifts regarding the orientation of the substituent (ii) analysis of stereospecific long-range coupling constants Vh,h and Vc,h (iii) relaxation parameters such as NOE and spin-lattice relaxation time (T,) (iv) LIS experiments at H and C frequencies. The results obtained... [Pg.284]

The n-site Bloch-McConnell equations describe the evolution of nuclear spin magnetization in the laboratory or rotating frames of reference for molecules subject to chemical or conformational interconversions between n species with distinct NMR chemical shifts. Trott and Palmer used perturbation theory to approximate the largest eigenvalue of the Bloch-McConnell equations and obtain analytical expressions for the rotating-frame relaxation rate constant and for the laboratory frame resonance frequency and transverse relaxation rate constant. The perturbation treatment is valid whenever the population of one site is dominant. The new results are generally applicable to investigations of kinetic processes by NMR spectroscopy. [Pg.232]