Ab initio IPPP-CLOPPA approach to perform bond contribution analysis of NMR coupling constants: 1J(NH) in NH3 as a function of pyramidality
A method designed to analyse transmission mechanisms of NMR indirect spin-spin coupling constants based on the use of localized molecular orbitals and inner-projections of the polarization propagator at the RPA level has been implemented within an ab initio approach. Former semi-empirical versions o...
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| Autores principales: | , , , |
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| Formato: | JOUR |
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_01661280_v433_n1-3_p141_RuizDeAzua |
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| Sumario: | A method designed to analyse transmission mechanisms of NMR indirect spin-spin coupling constants based on the use of localized molecular orbitals and inner-projections of the polarization propagator at the RPA level has been implemented within an ab initio approach. Former semi-empirical versions of this approach proved to be a valuable tool to obtain insight on transmission mechanisms of NMR parameters. The new features and difficulties found in the implementation of this method at an ab initio level are discussed. In particular, a localization procedure is proposed to deal with vacant molecular orbitals. In order to convey an idea about the potentialities of this approach, in this work a bond contribution analysis of the 1J(NH) coupling in NH3 as a function of the pyramidality at the N atom is carried out. The influence of the N lone-pair, the different N-H bonds and the N inner-shell electrons in the coupling transmission are discussed, for pyramidal and planar configurations. Trends that are expected to be of general validity are found. Results obtained are in agreement with previous theoretical studies on 1J couplings as well as with empirical trends deduced from experimentally measured values of 1J(NH) couplings in different compounds. © 1998 Elsevier Science B.V. All rights reserved. |
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