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Media type:
E-Article
Title:
Hydrogen–Hydrogen Bonding in Planar Biphenyl, Predicted by Atoms‐In‐Molecules Theory, Does Not Exist
Contributor:
Poater, Jordi;
Solà, Miquel;
Bickelhaupt, F. Matthias
Published:
Wiley, 2006
Published in:
Chemistry – A European Journal, 12 (2006) 10, Seite 2889-2895
Language:
English
DOI:
10.1002/chem.200500850
ISSN:
1521-3765;
0947-6539
Origination:
Footnote:
Description:
<jats:title>Abstract</jats:title><jats:p>Based on an Atoms‐in‐Molecules (AIM) analysis, Matta et al. (<jats:italic>Chem. Eur. J.</jats:italic><jats:bold>2003</jats:bold>,<jats:italic>9</jats:italic>, 1940) recently claimed evidence for the existence of hydrogen–hydrogen bonding between<jats:italic>ortho</jats:italic>‐hydrogen atoms, pointing towards each other from adjacent phenyl groups in planar biphenyl. This AIM result is opposed to the classical view that nonbonded steric repulsion between the<jats:italic>ortho</jats:italic>‐hydrogen atoms is responsible for the higher energy of the planar as compared to the twisted geometry of biphenyl. In the present work, we address the question if hydrogen–hydrogen bonding in biphenyl exists, as suggested by AIM, or not. To this end, we have analyzed the potential energy surface for internal rotation of biphenyl in terms of two interacting phenyl radicals using density functional theory (DFT) at BP86/TZ2P. A detailed analysis of the bonding mechanism and a quantitative bond energy decomposition in the framework of Kohn–Sham DFT show that Pauli (or overlap) repulsion, mainly between C<jats:sup><jats:italic>ortho</jats:italic></jats:sup>H<jats:sup><jats:italic>ortho</jats:italic></jats:sup>phenyl MOs, prevents biphenyl from being planar and forces it to adopt a twisted equilibrium geometry. Furthermore, a derivative of biphenyl in which all four<jats:italic>ortho</jats:italic>‐hydrogen atoms have been removed<jats:italic>does</jats:italic>adopt a planar equilibrium geometry. Thus, our results confirm the classical view of steric repulsion between<jats:italic>ortho</jats:italic>‐hydrogen atoms in biphenyl and they falsify the hypothesis of hydrogen–hydrogen bonding.</jats:p>