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Spin–spin coupling across intramolecular NH + N hydrogen bonds in models for proton sponges: an ab initio investigation
Author(s) -
Del Bene Janet E.,
Alkorta Ibon,
Elguero José
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2199
Subject(s) - chemistry , intramolecular force , hydrogen bond , intermolecular force , proton , ab initio , excited state , ab initio quantum chemistry methods , coupling constant , crystallography , computational chemistry , spin (aerodynamics) , bond length , atomic physics , ground state , hydrogen , stereochemistry , molecule , physics , thermodynamics , crystal structure , quantum mechanics , organic chemistry
Abstract Ab initio calculations have been performed to obtain structures and coupling constants 1 J (NH), 1h J (HN), and 2h J (NN) for models of proton sponges with symmetric and asymmetric NH + N intramolecular hydrogen bonds (IMHBs). For a given model, the asymmetric structure has a lower energy, a longer NN distance, and a hydrogen bond which has a greater deviation from linearity. The computed values of 2h J (NN) for the models are significantly less than predicted values based on the distance dependence of 2h J (NN) for complexes with intermolecular NH + N hydrogen bonds. However, the reduced values of 2h J (NN) cannot be attributed solely to the distortion of the hydrogen bond in the models, but also reflect differences in s electron populations at the nitrogens in both the ground state and the excited states which couple to it through the Fermi‐contact (FC) operator. Values of 2h J (NN) for IMHBs can be related quadratically to the NN distances in the models, and demonstrate that there is no discrepancy between computed values of 2h J (NN) at the short NN distances found in these systems and experimental data for proton sponges. Copyright © 2008 John Wiley & Sons, Ltd.