Fluorine as a π donor.: Carbon 1s photoelectron spectroscopy and proton affinities of fluorobenzenes

被引:48
作者
Carroll, TX
Thomas, TD [1 ]
Bergersen, H
Borve, KJ
Sæthre, LJ
机构
[1] Oregon State Univ, Corvallis, OR 97331 USA
[2] Keuka Coll, New York, NY 14478 USA
[3] Uppsala Univ, S-75105 Uppsala, Sweden
[4] Univ Bergen, N-5020 Bergen, Norway
关键词
D O I
10.1021/jo0523417
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The carbon 1s ionization energies for all of the carbon atoms in 10 fluorine-substituted benzene molecules have been measured by high-resolution photoelectron spectroscopy. A total of 30 ionization energies can be accurately described by an additivity model with four parameters that describe the effect of a fluorine that is ipso, ortho, meta, or para to the site of ionization. A similar additivity relationship describes the enthalpies of protonation. The additivity parameters reflect the role of fluorine as an electron-withdrawing group and as a pi-electron donating group. The ionization energies and proton affinities correlate linearly, but there are four different correlations depending on whether there are 0, 1. 2, or 3 fluorines ortho or para to the site of ionization or protonation. That there are four correlation lines can be understood in terms of the ability of the hydrogens at the site of protonation to act as a pi-electron acceptor. A comparison of the ionization energies and proton affinities, together with the results of electronic structure calculations, gives insight into the effects of fluorine as an electron-withdraw in a group and as a pi donor, both in the neutral molecule and in response to an added positive charge.
引用
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页码:1961 / 1968
页数:8
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