A further look at π-delocalization and hydrogen bonding in 2-arylmalondialdehydes. Issue 1 (7th January 2016)

• Record Type: Journal Article
• Authors: Romero-Fernández, María P.; Ávalos, Martín; Babiano, Reyes; Cintas, Pedro; Jiménez, José L.; Palacios, Juan C.
• Is Part Of: Tetrahedron. Volume 72:Issue 1(2016)
• Page Start: 95
• Page End: 104
• Publication Date: 2016-01-07
• Subjects: RAHB -- Hydrogen bond -- Malondialdehydes -- Aromaticity -- Delocalization -- DFT; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2015.11.006
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: This paper examines in detail the tautomerism of 2-aryl-substituted malondialdehydes, mainly focused on enolal structures, by means of gas-phase and solvent-based DFT calculations performed at the M06-2X/6-311++G(d, p) level. Open and pseudo-cyclic structures can be envisaged, the latter being decorated by an intramolecular hydrogen bond acting in symbiosis with π-electron delocalization. We have checked the relationship between the computed hydrogen bond energies and a variety of descriptors for electron delocalization. Application of the natural bond orbital (NBO) method to interrogate the nature of donor-acceptor interactions unravels that stabilization energies mainly arise from lone-pair and σ-antibonding interactions. Transition structures involved in proton transfer along the reaction pathway could be identified andTS exhibit a nearly complete electron delocalization characteristic of aromatic systems. All data gathered herein provide a description of quasi-aromaticity more consistent with hydrogen-bonding-assisted resonance (HBAR) than the widely held RAHB ( resonance-assisted hydrogen bonding ) formalism. Overall, the paper does not invoke a new concept, but rather the fact that the effects of H-bonding on delocalization and the effects of the latter on H-bonding can accurately be captured by computation, yet representing two sides of the same coin. Graphical abstract: