SCF molecular orbitals and the photoelectron spectrum of 5,5-dimethyl-Δ3-1,3,4-oxadiazolin-2-one
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abstract
CNDO/2 Frontier molecular orbital densities, ionization potentials (IP's), and electronic transition energies were calculated for the title compound (2b) and the 5,5-diprotio (2a), and 5,5-difluoro (2d) analogs. Bond lengths and angles were not optimized but rather taken from a crystal structure of the 2-imino System 3, with an assumed carbonyl bond length of Rco = 1.19 Å. This value is supported by a high infrared stretching frequency (1835 cm−1), X-ray crystal data of 3, and the effect of Rco variation on calculated IP's. The first three bands of the photoelectron spectrum of 2b were assigned as nN− (10.20 eV), π1 (11.52eV), and nco (13.26 eV) (vertical IP's). This unusually large nco IP is attributed to an inductive effect of the neighbouring strongly electron withdrawing azo group. The IP's obtained by CNDO/2 calculation (12.81, 13.37, and 15.15) are 1.5 to 2.5 eV higher than the experimental values, well within the predictive capability of the method, establishing that this theoretical treatment gives a good representation of the MO's of 2b.
