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961.
It is shown that by a suitable choice of the bound- and continuum-state functions used to perform shell-model calculations, the continuum-continuum interaction may be minimized. Approximate expressions for the scattering matrix elements are derived that are easily evaluated by simple extensions of the conventional shell-model calculations for bound states. Numerical calculations are performed for neutron scattering from 12C within the framework of the deformed rotor model and compared with exact coupled-channel calculations. 相似文献
962.
963.
964.
Iodination of selected 1-allyl- or 1-benzyl-cyclopropenes with electron-donating groups on the substituent leads to 2-iodo-1-iodomethyl-1 -vinyl or 1-arylcyclopropanes. 相似文献
965.
In the present note we outline a truncation scheme for configuration space ofN-electron systems in definite spin statesS for Hubbard Hamiltonian with first neighbour transfer terms. For this sparse matrix we find that the present truncation scheme
yields reasonably good ground and first excited states with very limited space being used. 相似文献
966.
967.
Separation of amino acids by thin-layer chromatography 总被引:2,自引:0,他引:2
968.
The 1H NMR spectra of 24 compounds containing the ester group are given and assigned. These data were used to investigate the effect of the ester group on the 1H chemical shifts in these molecules. These effects were analysed using the CHARGE model, which incorporates the electric field, magnetic anisotropy and steric effects of the functional group for long-range protons together with functions for the calculation of the two- and three-bond effects. The effect of the ester electric field was given by considering the partial atomic charges on the three atoms of the ester group. The anisotropy of the carbonyl group was reproduced with an asymmetric magnetic anisotropy acting at the midpoint of the carbonyl bond with values of Deltachi(parl) and Deltachi(perp) of 10.1 x 10(-30) and -17.1 x 10(-30) cm3 molecule(-1). An aromatic ring current (=0.3 times the benzene ring current) was found to be necessary for pyrone but none for maleic anhydride. This result was confirmed by GIAO calculations. The observed 1H chemical shifts in the above compounds were compared with those calculated by CHARGE and the ab initio GIAO method (B3LYP/6-31G**). For the 24 compounds investigated with 150 1H chemical shifts spanning a range of ca 10 ppm, the CHARGE model gave an excellent r.m.s. error (obs - calc) of <0.1 ppm. The GIAO calculations gave a very reasonable r.m.s. error of ca 0.2 ppm although larger deviations of ca 0.5 ppm were observed for protons near to the electronegative atoms. The accurate predictions of the 1H chemical shifts given by the CHARGE model were used in the conformational analysis of the vinyl esters methyl acrylate and methyl crotonate. An illustration of the use of the CHARGE model in the prediction of the 1H spectrum of a complex organic molecule (benzochromen-6-one) is also given. 相似文献
969.
970.
Istvn Lengyel David B. Uliss M. Mehdi Nafissi-V John C. Sheehan 《Journal of mass spectrometry : JMS》1969,2(12):1239-1255
The electron-impact induced fragmentation of eight aziridinones has been studied by conventional as well as by high resolution mass spectrometry. All α-lactams exhibit a molecular ion. The major primary step, in the fragmentation, is the ejection of carbon monoxide from the molecular ion. Ions of the general formula R1? NC and R2R3C?O were found in the mass spectra of all α-lactams investigated. A skeletal rearrangement to rationalize these ions is proposed. The fragmentation of the molecular ion is affected by the N-substituent. Exact mass measurement and specific deuterium labeling indicate the absence of McLafferty rearrangement from either the N- or C-substituent. 相似文献