Issue 8, 2002

A theoretical study on the homolytic dissociation energies of H–N+ bonds

Abstract

Various levels of theoretical calculations were performed to study the N+–H bond dissociation energies (BDEs) of protonated amines in order to check the experimental results and to investigate the substituent effects. It was found that the reported experimental N+–H BDEs in the gas phase are possibly not accurate. Our best predictions on the basis of CBS-Q and G3 calculations for the N+–H BDEs of NH4+, CH3NH3+, (CH3)2NH2+, (CH3)3NH+, PhNH3+, and pyridinium are 125 ± 1, 110 ± 1, 107 ± 1, 95 ± 1, 75 ± 2, and 124 ± 1 kcal mol−1, respectively. In agreement with a previous study, it was also found that the solvent effects on the N+–H homolysis in acetonitrile are large, which significantly increases the N+–H BDEs compared to the gas phase. Further studies on the N+–H BDEs of protonated para-substituted anilines indicated that the substituent effects should have a slope of about 8.7 kcal mol−1 against the substituent σp+ constants. This value is larger than that for the O–H BDEs of phenols (6.7–6.9 kcal mol−1) and N–H BDEs of neutral anilines (3.0 kcal mol−1). The pattern of substituent effects is also completely different from that for the C–H BDEs of toluenes, as the C–H BDEs of toluenes are reduced by both the electron-withdrawing and -donating groups. Thus, we concluded that it is the electron demand of the system that dictates the substituent effects on BDEs. For the protonated aniline case, the origin of the substituent effects was found to be that an electron-withdrawing group destabilizes X–C6H4–NH2+˙ more than X–C6H4–NH3+, whereas an electron-donating group stabilizes X–C6H4–NH2+˙ more than X–C6H4–NH3+.

Graphical abstract: A theoretical study on the homolytic dissociation energies of H–N+ bonds

Supplementary files

Article information

Article type
Paper
Submitted
08 May 2002
Accepted
07 Jun 2002
First published
26 Jun 2002

J. Chem. Soc., Perkin Trans. 2, 2002, 1406-1411

A theoretical study on the homolytic dissociation energies of H–N+ bonds

Y. Cheng, L. Liu, K. Song and Q. Guo, J. Chem. Soc., Perkin Trans. 2, 2002, 1406 DOI: 10.1039/B204417J

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements