title: Are unsaturated isocyanides so different from the corresponding nitriles?
abstract: Simple unsaturated and cyclopropylic isocyanides are synthesized by an efficient and simple approach. These compounds with gradually increasing distance between the unsaturated moiety and the isonitrile group are studied by UV photoelectron spectroscopy and quantum chemical calculations, and also compared to the corresponding nitriles. The first photoelectron band of the unsaturated compounds is linked to removal of an electron from the HOMO, which corresponds to CC multiple-bond ionization in antibonding interaction with the π-isocyanide bond (in the same plane) for conjugated systems, or in antibonding interaction with the pseudo-π-CH(2) group for isolated systems. For the 1-ethenyl derivatives, both cyano and isocyano groups act as a π-electron acceptor from the vinyl group, but the isocyano π system is much more strongly destabilized (ionization energies (IEs) shift to smaller values) by vinyl (3.12 eV) than the cyano π system is (2.70 eV). In comparison with the 1-ethynyl derivatives, a less pronounced destabilization (2.69 eV) of π(NC) by the ethynyl system (1.86 eV for π(CN)), and nearly the same order of magnitude of the energetic gap between the total antibonding (π(CC)-π(NC)) and the total bonding (π(CC)+π(NC)) IEs for ethenyl and ethynyl compounds are noted. The huge values of these last-named data for H(2)C=CH-NC (3.85 eV) and for HC≡C-NC (4.04 eV) reflect the strong interaction between the unsaturated carbon-carbon moiety and the isocyanide group, and thus more efficient conjugation than for the corresponding nitriles.
authors.affiliation: Université de Pau et des Pays de l'Adour, CNRS, UMR 5254-IPREM-Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, 2 avenue du Président Angot-Pau, 64053, France. anna.chrostowska@univ-pau.fr
authors.forename: Anna
authors.initials: A
authors.lastname: Chrostowska
authors.forename: Abdellatif
authors.initials: A
authors.lastname: Matrane
authors.forename: Daisuke
authors.initials: D
authors.lastname: Maki
authors.forename: Said
authors.initials: S
authors.lastname: Khayar
authors.forename: Hideharu
authors.initials: H
authors.lastname: Ushiki
authors.forename: Alain
authors.initials: A
authors.lastname: Graciaa
authors.forename: Larbi
authors.initials: L
authors.lastname: Belachemi
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Guillemin