Bay-type H···H "bonding" in cis-2-butene and related species: QTAIM versus NBO description

• Published in: Journal of computational chemistry Vol. 35; no. 20; pp. 1499 - 1508
• Main Authors: Weinhold, Frank, Schleyer, Paul von Ragué, McKee, William Chadwick
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 30.07.2014
• Subjects: bond critical point; chemical bonding; hyperconjugation; natural bond orbital theory; quantum theory of atoms in molecules theory; steric repulsion; steric repulsion; quantum theory of atoms in molecules theory; bond critical point; hyperconjugation; natural bond orbital theory; chemical bonding
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.23654

We use comparative natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) methods to analyze the proximal bay‐type H···H interactions in cis‐2‐butene and related species, which lead to controversial interpretation as attractive “HH bonding” in the QTAIM framework. We address the challenging questions concerning well established structural, conformational, and vibrational properties of such species that appear to be sharply at odds with the QTAIM interpretation. In contrast to the purported “HH bonding” of QTAIM theory, NBO‐based evaluation of steric (donor–donor) and hyperconjugative (donor–acceptor) interactions unambiguously portrays such H···H contacts as dominated by steric clashes that are only partially softened by weak secondary hyperconjugative interactions, contributing negligibly (bHH < 0.01) to H···H bond order. Additional details of NBO‐based versus QTAIM‐based description are provided by natural bond critical point analysis of topological bond critical point properties, which further emphasizes the contrast between the problematic bay‐type H···H contacts and remaining noncontroversial (consensus) chemical bonds. NBO analysis is thereby shown to be fully consistent with the traditional physical organic concept of repulsive bay‐type H···H contacts, including the corollary array of structural, conformational, and vibrational properties. © 2014 Wiley Periodicals, Inc. NBO assessment of donor–donor (steric) versus donor–acceptor (resonance‐type) contributions confirms the predominantly repulsive nature of bay‐type σCH‐σCH interactions in cis‐2‐butene and related species, contrary to QTAIM‐based claims of net “H···H bonding” attraction.