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Are Unsaturated Isocyanides so Different from the Corresponding Nitriles?
Author(s) -
Chrostowska Anna,
Matrane Abdellatif,
Maki Daisuke,
Khayar Said,
Ushiki Hideharu,
Graciaa Alain,
Belachemi Larbi,
Guillemin JeanClaude
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100672
Subject(s) - chemistry , antibonding molecular orbital , isocyanide , moiety , conjugated system , nitrile , photochemistry , medicinal chemistry , crystallography , computational chemistry , stereochemistry , electron , organic chemistry , atomic orbital , physics , polymer , quantum mechanics
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 CCHNC (3.85 eV) and for HCCNC (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.