Why Selenoxanthone Gives an MC with Bromine: An Examination of Electronic States of Xanthones and Xanthenes by Electron Spectroscopy and ab Initio MO Calculations
1998; American Chemical Society; Volume: 63; Issue: 23 Linguagem: Inglês
10.1021/jo9812734
ISSN1520-6904
AutoresWarô Nakanishi, Satoko Hayashi, Yoshiaki Kusuyama, Takeshi Negoro, Shigeru Masuda, Hideki Mutoh,
Tópico(s)Advanced Chemical Physics Studies
ResumoThe PIES and UPS spectra of xanthone (1a), thioxanthone (1b), and selenoxanthone (1c) were measured, together with those of the corresponding xanthene (2a), thioxanthene (2b), and selenoxanthene (2c). Ab initio MO calculations were performed with the 6-311+G(d,p) basis sets at the DFT (B3LYP) level on 1a−c and 2a−c. The results of the measurements and of the MO calculations explained well the striking difference in the reactivity of the compounds, especially for 1c versus 2c. The ionization potentials (IP) of π6(n) (HOMO), n(pz) (π2(n) for 1a and 2a), and n(py) were in the order IP(1a) > IP(1b) > IP(1c) and IP(2a) > IP(2b) > IP(2c). The IP of the xanthones were larger than those of the corresponding xanthenes. The IP of n(pz) of 1c was demonstrated to be larger than those of 2b and PhSPh (3b), which showed that 1c was less reactive than 2b and 3b toward electrophiles. These results accounted for the reactivity of 1c to give a molecular complex (MC) with bromine similar to the case of the MC structure of the sulfide dibromides. The relative intensity of PIES of HOMO in 1c was smaller than that in 2c. The electron density outside the molecular surface of the orbital of 1c must be smaller than that of 2c, due to the strong electron-withdrawing carbonyl group in 1c, which was supported by the calculated natural populations at the chalcogen atoms of the compounds.
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