A LINEAR RELATION BETWEEN THE IONIZATION-POTENTIALS OF HEI PHOTOELECTRON-SPECTROSCOPY AND NMR CHEMICAL-SHIFTS - A PES STUDY OF THE ELECTRONIC-STRUCTURE OF ALKYL ISOCYANIDES

HeI photoelectron (PES) of alkyl isocyanides RNC, where R is -CH3, -CH 2CH3, -CH2CH2CH3, -CH(CH3)(2), -C(CH3)(3) and -cyclo-C6H11, are report ed. The assignment of the bands is made with the aid of bandshapes, fi ne vibrational structure and ab initio SCF MO calculations with STO-6G basis sets for each of the molecules studied. The first sharp peak wi th the lowest ionization potential and with different vibrational spac ings is assigned to electron ionization of the HOMO which is composed of a dominant contribution of the carbon atom, similar to the 'lone-pa ir' orbital or the carbon atom in the isocyano group. A linear relatio nship between the lowest PES experimental ionization potentials and th e C-13 NMR chemical shifts of the carbon in the isocyano group is foun d.