A Quantitative Scale for the Degree of Aromaticity and Antiaromaticity: A Comparison of Theoretical and Experimental Enthalpies of Hydrogenation
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- 作者：Zoltá ; n Mucsi ; Bé ; la Viskolcz ; Imre G. Csizmadia
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：February 15, 2007
- 年：2007
- 卷：111
- 期：6
- 页码：1123 - 1132
- 全文大小：256K
- 年卷期：v.111,no.6(February 15, 2007)
- ISSN：1520-5215
文摘
Chemical structures and transition states are often influenced by aromatic stabilization or antiaromaticdestabilizing effects, which are not easy to characterize theoretically. The exact description and precisequantification of the aromatic characteristics of ring structures is difficult and requires special theoreticalinvestigation. The present paper suggests a novel, yet simple, method to quantify both aromatic and antiaromaticqualities on the same linear scale, by using the experimentally measured or theoretically computed enthalpyof hydrogenation reaction of the compound examined [
HH2(examined)]. A reference hydrogenation reactionis also considered on a corresponding nonaromatic reference compound [HH2(reference)] to cancel allsecondary structure destabilization factors, such as ring strain or double bond strain. From these data therelative enthalpy of hydrogenation may easily be calculated: HH2 = HH2(examined) - HH2(reference).In the present work concept, the HH2 value of benzene defines the completely aromatic character (+100%),and the closed shell of the singlet cyclobutadiene represents maximum antiaromaticity (-100%). The componentHH2 values were computed at different levels of theory offering a computational "method-independent"measure for aromaticity. A total of 28 well-known aromatic, antiaromatic and nonaromatic, neutral and chargedcompounds were examined to demonstrate the efficiency of this methodology. Finally, a correlation wasmade between the calculated aromaticity percentage of the compound examined and their popular SchleyersNICS values.
HH2(examined)]. A reference hydrogenation reactionis also considered on a corresponding nonaromatic reference compound [HH2(reference)] to cancel allsecondary structure destabilization factors, such as ring strain or double bond strain. From these data therelative enthalpy of hydrogenation may easily be calculated: HH2 = HH2(examined) - HH2(reference).In the present work concept, the HH2 value of benzene defines the completely aromatic character (+100%),and the closed shell of the singlet cyclobutadiene represents maximum antiaromaticity (-100%). The componentHH2 values were computed at different levels of theory offering a computational "method-independent"measure for aromaticity. A total of 28 well-known aromatic, antiaromatic and nonaromatic, neutral and chargedcompounds were examined to demonstrate the efficiency of this methodology. Finally, a correlation wasmade between the calculated aromaticity percentage of the compound examined and their popular SchleyersNICS values.