Tamio Yasukawa

Steric effects on the dynamical behaviour and 13C nuclear spin relaxation in flexible chain molecules

Abstract Steric effects on the dynamical behaviour and 13 C nuclear spin relaxation in flexible chain molecules have been examined by simulating the random motions of n -hexylamine coordinated to Gd(FOD) 3 with several models by the Monte Carlo technique. The spectral density functions were calculated for the respective carbons of the hexyl group and power densities at the Larmor frequency were compared with experimental values of T 1M . Simulation models where the pentane effect is taken into considerations gave satisfactory results.

Solvent effects on the coupling processes of polystyryl radicals

The molecular weight distributions of polystyrene prepared in various solvents at 60 °C showed broadening with increasing solvent viscosity, whereas the effects of solvent power were not conspicuous. Simulations of polymerization reactions with several models showed that the coupling probability of polystyryl radicals is not independent of chain length at 60 °C and that the chain length dependence becomes apparent with increasing solvent viscosity. These results were discussed in terms of the dynamical behavior of polymer radicals in solution and it was tentatively concluded that the chain length dependence of coupling probability of polystyryl radicals originates mainly from the hydrodynamic interactions between polymer segments.

Chain length dependence of termination rate constant: computer experiment of effects on the kinetics of radical polymerization of styrene

Abstract The kinetics of the radical polymerization of styrene, initiated by AIBN, have been studied by computer experiments. The models adopted assume a termination rate constant for polystyryl radicals with degrees of polymerization m and n , given by: k t,mn =k α m -α n -α Deviations from simple kinetic rules have been found for α ≉ 0.0 . For example, the rate of polymerization is roughly proportional to the 0.45 power of initiator concentration for α = 0.1. Conventional methods for the kinetic study of radical polymerizations are shown to come to erroneous conclusions if the effects of the chain length dependence of termination rate constant are not taken into account.

Hyperfine couplings and 13C relaxation in alkylamines coordinated to Ni(II) acetylacetonate

The conformational dependence of the proton and carbon-13 hyperfine coupling constants in aliphatic amines coordinated to Ni(AA)2 has been investigated by N.M.R. contact shift measurements. It is shown that the hyperfine coupling constants a C β and a H β are given by with B 1 H=10·5 G, B 2 H=10·6 G, B 1 C=-4·9 G, B 2 C=13·1 G where ϑ is the torsion angle about the C1-N bond. The experimental values of a H β and a C β in the ethylamine-Ni(AA)2 complex have been compared with those calculated from the above expression and the potential function computed by INDO for the rotation of C2H5 about the N-C1 bond in EtNH2 +. Good agreement is obtained for a potential barrier V 0 = 15·5 kJ mol-1. The 13C paramagnetic relaxation rates T 1M -1 and T 2M -1 in the complexes have also been determined. For n-butyl and n-hexylamine complexes, the dipolar longitudinal relaxation rates have been calculated from Monte Carlo simulations of random fluctuations of the magnetic field due to internal and overall motions and to el...

Carbon-13 nuclear spin relaxation induced by the electron spin delocalized through sigma bonds in n-hexylamine coordinated to Ni(acac)2

Abstract The 13C T1 in n-hexylamine coordinated to Ni(acac)2 have been calculated by simulating random dipolar interactions with Ni2+ ion and protons. Satisfactory results were obtained for all carbons except C2 where T1 is abnormally short. This discrepancy has been attributed to an unsymmetrical distribution of the electron spin around the C2 nucleus.

An efficient Monte Carlo method to calculate nuclear spin relaxation times in complex molecules

Abstract An efficient Monte Carlo method to calculate nuclear spin relaxation times and nuclear Overhauser enhancements in complex molecules based on the convolution of power spectra for independent processes is proposed and applied to analyze the 13 C T 1 distribution in poly(N-hexy-4-vinylpyridinium) bromide.