Atsuo Nishioka

Solvent effect study of the13C chemical shifts of acetonitrile and acetone using the “Solvaton” model

Abstract The 13 C chemical shifts of acetonitrile and acetone, as calculated by Poples GIAO-MO theory and application of Klopmans “solvaton” model to the MINDO/2-MO method, agree well with the observed solvent effects, including the temperature dependence of the chemical shift.

Theoretical calculation of carbon-13 NMR shielding constants and their tensors in hydrocarbons by the finite perturbation method

Abstract The 13 C chemical shifts and their tensors in hydrocarbons are calculated by means of the finite perturbation method together with a semiempirical INDO molecular orbital method. By a small revision of the formula for the off-diagonal elements of the core Hamiltonian matrix in the INDO method, the calculated results show fairly good agreement with the gross trends of the observed values of 13 C chemical shifts and shielding tensors. The inclusion of the effects from neighboring atoms yields better agreement between the observed and calculated values of the shifts in methyl substituents of olefins.

Theoretical calculation of 13C chemical shielding anisotropy in some organic compounds

Abstract The 13 C chemical shielding anisotropies of benzene, toluene, hexamethylbenzene and acetone molecules are calculated theoretically by a linear combination of gauge invariant atomic orbitals — molecular orbital theory using the MINDO method. They are found to agree with the experimental data measured by Pines et al.

Calculation of proton N.M.R. chemical shifts by means of a finite perturbation method

The magnetic shielding effect due to neighbouring carbon atoms through the diamagnetic and paramagnetic terms is calculated by means of a finite perturbation method in cooperation with a semi-empirical INDO molecular orbital method. The behaviour of the components of the shielding tensor arising from 2s and 2p orbitals centred on a neighbouring carbon is shown as a function of the distance, R, between the proton considered and the carbon. It is pointed out that the treatment by Pople and McConnell in the calculation of the proton chemical shift must be used carefully in unsaturated hydrocarbons, because some of the contributions from a neighbouring carbon do not show an R -3 dependence but an R -2 dependence. It is also shown that the gross trend of the observed proton chemical shifts in hydrocarbons is reproduced fairly well in the present calculation.

Spin-lattice relaxation of norbornadiene and 1,3-indandione in solution

Abstract The proton spin-lattice relaxation times T 1 of the three nonequivalent protons of norbornadiene (bicyclo[2.2.1 ]hepta-2,5-diene) in chloroform- d were measured by the adiabatic rapid passage method over the temperature range 25–80°C. By a dilution procedure the intra- and intermolecular relaxation times [( T 1 ) intra and ( T 1 ) inter ] were obtained. The rotational and translational correlation times ( τ c and τ t ), and the rotational diffusion constants at 25°C indicate that the rotational and translational motions are fully isotropic. The activation energies estimated from the temperature dependence of ( T 1 ) intra or ( T 1 ) inter of the three protons are also identical. The τ c value predicted by Hills mutual-viscosity theory is in good agreement with the experimental one. T 1 s of the two nonequivalent protons of 1,3-indandione in chloroform- d were also measured, and the effect of the anisotropic molecular motion on the proton spin-lattice relaxation and its temperature dependence was investigated.

High-resolution spin-lattice relaxation time measurement by saturation recovery method with on-line mini-computer

Abstract A modified saturation recovery method is proposed for the measurement of the spin-lattice relaxation time (T1) of individual lines in a high resolution NMR spectrum using a conventional high-resolution NMR instrument attached to a mini computer. It is conveniently applicable to measuring T1 accurately, especially in the range between 1 sec and 50 msec. The relaxation times obtained for poly-γ-methyl- l -glutamate in trifluoroacetic acid were T1 (OCH3) = 260 msec, T1 (α-CH) = 100 msec, and T1 (γ-CH) = 95 msec at 25°C.

1H N.m.r. relaxation and molecular motion of polyethylene in solution as studied by the isotopic dilution technique

Abstract The molecular motion of polyethylene has been studied in decalin-d 18 solution by 1 H n.m.r. relaxation with the isotopic dilution technique which can separate the proton spin-lattice relaxation times into the intra- and intermolecular contributions, intra T 1 and inter T 1 . The temperature dependences of intra and inter T 1 s show that the intra- and intermolecular motions are in the extreme narrow region. These results, also, were compared with the results of molten polyethylene reported in our previous work.

Conversion and Molecular Weight Dependences of the Tacticity of Poly (methyl methacylate) in a Radical Polymerizatio n

メタクリル酸メチルのラジカル重合物の立体規則度と重合率および分子量との関係を研究した。0℃,22.5℃,60℃および100℃で重合を行ない,立体規則度(トリアッド:I,H,S)はNMRスペクトルから求めた。低重合率ではこれらの値は重合率によらず一定であるが,高重合率ではSが若干減少し,IおよびHが増加した。また上記の試料の分子量分別物の立体規則度は高重合率試料の場合分子量により若干変化することが見出された。