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The Feynman path integral Monte Carlo approach has been coupled to the gauge including atomic orbital formalism in order to analyse the absolute magnetic shieldings of the benzene nuclei under the conditions of thermal equilibrium. The Hamiltonian employed in the derivation of ensemble averaged NMR quantities is of the Hartree-Fock type. The basis set used is of 6–31G quality. The spatial delocalization of the atoms leads to a deshielding of both types of benzene nuclei relative to the shieldings experienced at the minimum of the potential energy surface. This deshielding has to be traced back to bond length elongations in thermal equilibrium. The influence of the nuclear fluctuations on the NMR parameters of benzene is quantum driven up to temperatures of 400 K; classical fluctuations are of minor importance in this low-temperature window. 相似文献
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Rabbani MG Reich TE Kassab RM Jackson KT El-Kaderi HM 《Chemical communications (Cambridge, England)》2012,48(8):1141-1143
Successful incorporation of triptycene into benzimidazole-linked polymers leads to the highest CO(2) uptake (5.12 mmol g(-1), 273 K and 1 bar) by porous organic polymers and results in high CO(2)/N(2) (63) and CO(2)/CH(4) (8.4) selectivities. 相似文献