Electronegativities from Core-Ionization Energies: Electronegativities of SF5 and CF3

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• 作者：Jan E. True ; T. Darrah Thomas ; Rolf W. Winter ; and Gary L. Gard
• 刊名：Inorganic Chemistry
• 出版年：2003
• 出版时间：July 14, 2003
• 年：2003
• 卷：42
• 期：14
• 页码：4437 - 4441
• 全文大小：64K
• 年卷期：v.42,no.14(July 14, 2003)
• ISSN：1520-510X

文摘

Core-ionization energies have been measured for SF₆ (S 2p), SF₅SF₅ (S 2p), SF₅Br (S 2p and Br 3d), and SF₅CF₃(S 2p and C 1s). These results, together with others that establish correlations between core-ionization energiesand Pauling electronegativities, make it possible to assign group electronegativities to SF₅ and CF₃. This methodgives electronegativities for these groups comparable to that of bromine, whereas analysis of the effect of thesegroups on acidity indicates electronegativities comparable to that of fluorine. Other methods of estimatingelectronegativity fall between these extremes. These disparities can be understood in part as reflecting the effectsof polarizibility of the substituent, which tends to lower both the core-ionization energy and the deprotonationenergy, making the electronegativity appear to be less in one case and more in the other. In addition, and possiblymore important, the core-ionization energies presented here reflect the effect of the group on an adjacent atom,whereas the acidity reflects the effect on a remote atom. It appears that fluorine has a large effect on an adjacentatom but a relatively small effect on a remote atom. By contrast SF₅ and CF₃ have a relatively small effect on anadjacent atom, but this effect falls off only slowly with distance from the substituent. Thus, the effectiveelectronegativities of CF₃ and SF₅ relative to those of the halogens depend on the site at which the molecule isprobed as well as on the process that is under consideration.