title: Pseudo-cyclic structures of mono- and di-azaderivatives of malondialdehydes. Synthesis and conformational disentanglement by computational analyses.
abstract: Mono- and diaza-derivatives of malondialdehydes, namely 3-alkyl(aryl)amino-2-arylacroleins and 1,5-dialkyl(aryl)-3-arylvinamidines are open-chain systems in which extended electron delocalization and pseudoaromaticity can be envisaged. A set of diversely functionalized compounds has been synthesized and characterized by spectroscopic data and X-ray diffractometry. Quantum-chemical calculations were performed for all possible neutral tautomers and conformers in the gas phase and compared to those in polar solvents (CHCl3, DMSO, and EtOH) at the M06-2X/6-311++G(d,p) level. Tautomeric equilibria and conformational preferences can be rationalized in terms of structural factors, which can be roughly estimated as summation or subtractions of intramolecular interactions. As expected, a key role is played by intramolecular hydrogen bonds whose strength varies from the gas phase to polar ethanol. This issue also delves into the concept of resonance-assisted H-bond, where the donor and acceptor atoms are connected by a π-conjugated system. The most stable conformers (structures a and c) possess a high degree of pseudoaromaticity as inferred from HOMA indexes and other delocalization parameters.
authors.affiliation: Departamento de Química Orgánica e Inorgánica, QUOREX Research Group, Facultad de Ciencias-UEX, Avda. de Elvas s/n, E-06006 Badajoz, Spain. mpromero@unex.es.
authors.forename: María P
authors.initials: MP
authors.lastname: Romero-Fernández
authors.forename: Martín
authors.initials: M
authors.lastname: Ávalos
authors.forename: Reyes
authors.initials: R
authors.lastname: Babiano
authors.forename: Pedro
authors.initials: P
authors.lastname: Cintas
authors.forename: José L
authors.initials: JL
authors.lastname: Jiménez
authors.forename: Mark E
authors.initials: ME
authors.lastname: Light
authors.forename: Juan C
authors.initials: JC
authors.lastname: Palacios