Spin–spin coupling across intramolecular NH+N hydrogen bonds in models for proton sponges: an ab initio investigation

✍ Scribed by Janet E. Del Bene; Ibon Alkorta; José Elguero

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 183 KB
• Volume: 46
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.2199

✦ Synopsis

Abstract

Ab initio calculations have been performed to obtain structures and coupling constants ^1^J(NH), ^1h^J(HN), and ^2h^J(NN) for models of proton sponges with symmetric and asymmetric NH^+^N intramolecular hydrogen bonds (IMHBs). For a given model, the asymmetric structure has a lower energy, a longer NN distance, and a hydrogen bond which has a greater deviation from linearity. The computed values of ^2h^J(NN) for the models are significantly less than predicted values based on the distance dependence of ^2h^J(NN) for complexes with intermolecular NH^+^N hydrogen bonds. However, the reduced values of ^2h^J(NN) 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(NN) for IMHBs can be related quadratically to the NN distances in the models, and demonstrate that there is no discrepancy between computed values of ^2h^J(NN) at the short NN distances found in these systems and experimental data for proton sponges. Copyright © 2008 John Wiley & Sons, Ltd.