The He(I)photoelectron spectra of cyclobutene‐1,2‐dione (1), o‐benzoquinone (4) and alkyl substitution products of 1 and 4 have been recorded. The first bands of the spectra have been assigned on the basis of molecular orbital calculations and qualitative band shape criteria.
The hexaketones (1) and (2), now synthesized for the first time, each have two vicinal tricarbonyl groups; as expected, they are found to be strong acceptors. Their halfwave potentials resemble the value for tetracyanoquinodimethane. (1) and (2) form 1:1 complexes with pyrene.
The He(1a) PE and the electronic absorption spectra of hexafluorocyclobutanone (3) and tetrafluoro-I ,2-cyclobutanedione (4) have been recorded. The assignment of the observed bands in both types of spectra is mainly based on the correlation with the corresponding spectra of the parent compounds cyclobutanone (1) and l ,2-cyclobutanedione (2), and in addition on the results of semiempirical calculations. As a result of the perfluoro effect, the bands in the PE spectra of 3 and 4 are shifted towards higher ionization energies by 1.6 eV and 1.5 eV relative to the corresponding bands in the PE spectra of 1 and 2. A comparison of the positions of the first band in the electronic spectra of 1 and 3, as well as of 2 and 4, shows that this band is shifted bathochromically by about 5000 cm-I as a consequence of the perfluoro substitution. This is explained as being due to a stronger lowering of the LUMO (x*) energy than that of the HOMO (n) energy, induced by the replacement of the H-by F-atoms.Die He(Ia)-PE-Spektren und Elektronenabsorptionsspek tren von Hexafluorcyclobutanon und Tetrafluor-1,2-cyclobutandion Die He(1a)-PE-Spektren und die Elektronenabsorptionsspektren von Hexafluorcyclobutanon (3) und Tetrafluor-I ,2-cyclobutandion (4) wurden gemessen. Die Zuordnung der ersten Banden beider Spektrentypen basiert hauptsachlich auf der Korrelation rnit den entsprechenden Spektren der unsubstituierten Verbindungen Cyclobutanon (1) und 1,2-Cyclobutandion (2) sowie auf den Resultaten semiempirischer Rechnungen. Die Banden in den PE-Spektren von 3 und 4 werden im Vergleich zu den PE-Banden von 1 und 2 durch den Perfluor-Effekt urn 1.6 bzw. 1.5 eV zu hoheren Energien verschoben. Vergleicht man die Energie der ersten Bande in den Elektronenspektren von 1 und 3 bzw. 2 und 4, so findet man, daR diese Bande bathochrom urn etwa 5000 cm-' durch die Perfluor-Substitution verschoben wird. Dies wird dadurch erklart, daf3 beim Ersatz der H-Atome durch F-Atome die Energie des LUMOs (n*) starker abgesenkt wird als die des HOMOS (n).The He(Ia) photoelectron (PE) spectra and the electronic absorption spectra of the titlecompounds hexafluorocyclobutanone (3) and tetrafluoro-I ,2-cyclobutanedione (4) are of some 0 VCH Verlagsgesellschaft mbH, D
siert orthorhombisch, Raumgruppe Pna2,, Z = 4151; die Cyangruppe ist fehlgeordnet (Besetzungsfaktoren = 0.50). Die Anordnung der Methylprotonen schlieBt die Moglichkeit aus, daB das Molekiil auf einer kristallographischen Spiegelebene liegt (was fur Pnam erforderlich ware).
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