Roderick E. Wasylishen

13C spin-lattice relaxation in rotationally disordered solids

13C spin-lattice relaxation times and 14N linewidths at selected temperatures in liquid and solid I (plastic) succinonitrile are reported. Effective rotational correlation times are derived from these and the results for solid I are discussed in terms of a model which assumes that the main contributions to the rotational disorder come from gauche↔trans isomerization and the jumping of the central C-C bond of the trans species between the 3-fold axes of the b.c.c. lattice. The general applicability of the 13C technique is emphasized and the results are compared with those of other experiments reported in the literature.

NMR investigation of orientationally disordered NaCN and KCN

Nitrogen‐14 NMR spin–lattice relaxation times are reported for the cubic phases of NaCN and KCN. The 14N T1 values of both compounds increase as temperature increase with apparent activation energies of 1.40±0.10 and 0.78±0.05 kcal/mole, respectively. The measured 14N T1 values indicate that T1≫T2 and that the rotational correlation times for cyanide reorientation are at least two orders of magnitude shorter than indicted in previous 14N studies. Carbon‐13 T1 values for KCN decrease with increasing temperature with an apparent activation energy of 1.38±0.2 kcal/mole and are interpreted assuming that the spin rotation mechanism dominates. Reduced correlation time τ2  and τJ  derived from the 14N and 13C data, respectively, are compared with those calculated using the J‐diffusion model which is quite successful for liquids.

Spin—Spin Coupling Between Carbon-13 and the First Row Nuclei

Publisher Summary This chapter focuses on the spin–spin coupling between Carbon-13 and the first row nuclei. The nuclear spin–spin coupling constant, n J(A-B) is a measure of the energy of interaction between the magnetic moments of nuclei A and B. The interaction is transmitted by a magnetic polarization of the electrons in the molecule and J is therefore an intrinsic second-order property of the molecule, depending, in a subtle manner, on the details of the electron distribution. Some of the theoretical approaches to the calculation of n J(A-B) are discussed. One of the most successful methods of calculating nuclear spin coupling constants involves the application of SCF perturbation theory and use of the INDO molecular orbital (MO) approximations.

A deuterium NMR study of orientational order in camphor

Abstract This investigation of the 2 H NMR absorption profile of D-camphor-3,3- d 2 demonstrates that the solid 1 (cubic)-solid II (rhombohedral) phase transition, through which complete rotational disorder was thought to be preserved, is actually accompanied by the onset of weakly preferred orientations. It is shown that throughout the temperature range of solid II, the spectra can be simulated by introducing temperature-dependent average order parameters analogous to those of liquid crystals and other partially ordered structures. Relaxation rates and angular correlation times are also presented for solid I.

A carbon-13 NMR study of carbon tetrabromide

Abstract 13C spin—lattice relaxation times and selected linewidths are reported for CBr4 (natural abundance) as determined by conventional techniques in the liquid, sold I (fcc, “plastic crystal”) and solid II (monoclinic, “rigid”) phases. The linewidths are less than 50 Hz and the T1s are between 0.5 and 1.5 s. Comments are made on the complexity of the relaxation of spin 1 2 nuclei by quadrupolar nuclei.

Natural abundance 13C nuclear magnetic resonance studies of live cestodes

1. Natural abundance carbon-13 nmr spectra of several intact cestodes have been obtained. 2. All spectra show peaks assignable to triglycerides and the N(CH3)3 carbons of the choline moiety. 3. The olefinic region of the 13C nmr spectra indicated that the cestode larvae Mesocestoides corti and Echinococcus multilocularis have a larger concentration of polyunsaturated fatty acids than Hymenolepis adults. 4. Mobile fragments of glycogen were detected in all species studied, but its apparent concentration in individual cestodes was highly variable.

Nitrogen‐14 NMR study of molecular motion in rubidium and cesium cyanide

Nitrogen‐14 nmr relaxation times T1Z, and T1Q of the cyanide ion in the cubic phase polycrystalline samples of RbCN and CsCN have been measured as a function of temperature. At any given temperature between 210 and 325 K the 14N spin‐lattice relaxation times in RbCN and CsCN are the same within experimental error. Assuming the quadrupolar relaxation mechanism, the relationship between T1Z and the rotational correlation time τ2 of the cyanide ion in these salts is calculated. The values of τ2 are short (e.g., ∼0.15 ps at 300 K) and only slightly longer than those calculated using an inertial rotational model. The 14N nmr T1Z data are compared with those previously obtained NaCN and KCN.