摘要：

The π ionization potentials of planar aromatic systems and their perfluoro derivatives are very nearly equal, whereas the σ ionization potentials in the perfluoro compounds are several electron volts larger than in the perhydro compound (the perfluoro effect). Comparisons of the high-resolution photoelectron spectra of benzene, pyridine, s-triazine, borazine, p-benzoquinone, and naphthalene with those of their perfluoro derivatives lead to the following conclusions. (a) In benzene, the orbital ordering is π3, π2 (1e1g, 9.421 eV), σ (3e2g, 11.49 eV), π1 (1a2u, 12.3 eV), while in hexafluorobenzene the ordering of oσ and π1 is reversed. (b) The lone-pair and π3 MO's of pyridine are nearly degenerate (9.67 and 9.80 eV), and their order cannot be deduced. These two MO's are followed by π2 (10.5 eV) and a σ MO at 12.45 eV which is a component of the 3e2g MO's of benzene. In pentafluoropyridine, the ordering is π3, π2, σ, π1. (c) The π3, π2 MO's of s-triazine show a slight Jahn-Teller split (11.71 and 12.15 eV), and are followed by the e′ (10.41 eV) and a1′ (13.25 eV) combinations of the nitrogen lone-pair AO's. π1 of s-triazine comes at 14.65 eV. In cyanuric fluoride, C3N3F3, π3, π2 are similarly split by 0.4 eV, and the π1 ionization precedes those from the lone pairs. (d) The uppermost MO's of borazine are π3, π2 rather than σ as suggested by other workers, and these are followed by σ and π1, as in benzene. (e) The first four ionizations in naphthalene are out of π MO's, the fifth out of a σ MO.

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