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Are Unsaturated Isocyanides so Different from the Corresponding Nitriles?

Authors

  • Prof. Dr. Anna Chrostowska,

    Corresponding author
    1. 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), Fax: (+33) 22323-8108
    • 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), Fax: (+33) 22323-8108
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  • Abdellatif Matrane ,

    1. Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7 (France)
    2. Laboratoire de Chimie Bio-Organique et Macromoléculaire, Faculté des Sciences et Techniques Marrakech, Université Cadi Ayyad, BP 549, Marrakech (Morocco)
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  • Daisuke Maki ,

    1. 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), Fax: (+33) 22323-8108
    2. Laboratory of Molecular Dynamics and Complex Chemical Physics, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183–8509 (Japan)
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  • Prof. Dr. Said Khayar,

    1. 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), Fax: (+33) 22323-8108
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  • Prof. Dr. Hideharu Ushiki,

    1. Laboratory of Molecular Dynamics and Complex Chemical Physics, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183–8509 (Japan)
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  • Prof. Dr. Alain Graciaa,

    1. Université de Pau et des Pays de l'Adour CNRS, TOTAL-UMR 5150-LFC-R, BP1155 Pau, 64013 (France)
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  • Prof. Dr. Larbi Belachemi,

    1. Laboratoire de Chimie Bio-Organique et Macromoléculaire, Faculté des Sciences et Techniques Marrakech, Université Cadi Ayyad, BP 549, Marrakech (Morocco)
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  • Dr. Jean-Claude Guillemin

    Corresponding author
    1. Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7 (France)
    • Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7 (France)
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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-CH2 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 πNC by the ethynyl system (1.86 eV for πCN), and nearly the same order of magnitude of the energetic gap between the total antibonding (πCC−πNC) and the total bonding (πCCNC) IEs for ethenyl and ethynyl compounds are noted. The huge values of these last-named data for H2C[DOUBLE BOND]CH[BOND]NC (3.85 eV) and for HC[TRIPLE BOND]C[BOND]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.

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