Cross‐correlated and conventional dipolar carbon‐13 relaxation in methylene groups in small, symmetric molecules

Abstract

AbstractA theory for dipolar cross‐correlated relaxation processes in AMX or AX2 spin system, with special reference to 13C‐methylene groups, is reviewed briefly. Simple experiments and protocols for measuring the transfer rates between the carbon‐13 Zeeman order and the three‐spin order, and for their analogues in the transverse plane, are discussed using a concentrated solution of the disaccharide trehalose as a model system. Experimental data sets consisting of conventional carbon‐13 relaxation parameters (T1, T2, and NOE), along with the cross‐correlated relaxation rates, are also presented for some small, rigid, polycyclic molecules. These data are interpreted using spectral density functions appropriate to spherical or symmetric tops reorienting according to small‐step rotational diffusion model. The analysis results in a consistent picture of the auto‐ and cross‐correlated spin relaxation processes. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 100–115, 2007.