Mills Nancy S, Llagostera Kathleen B, Tirla Cornelia, Gordon Stacey M, Carpenetti Donald
Department of Chemistry, Trinity University, San Antonio, Texas 78212-7200, USA.
J Org Chem. 2006 Oct 13;71(21):7940-6. doi: 10.1021/jo060346d.
Dications of p-substituted 3-phenylindenylidenefluorenes were prepared to examine the response of the resulting indenyl and fluorenyl cationic systems to magnetic measures of antiaromaticity. All measures, (1)H NMR shifts, nucleus independent chemical shifts (NICS(1)(zz)), and magnetic susceptibility exaltation, Lambda, supported the antiaromaticity of the dications 3a-f2+. The 1H NMR shifts and NICS(1)(zz) showed that the indenyl ring system was less antiaromatic than the fluorenyl ring system, contrary to the antiaromaticity of indenyl monocations compared to fluorenyl monocations. The presence of a phenyl substituent in the 3-position was able to stabilize the indenylidene cation through resonance, decreasing its antiaromaticity, but even in the absence of the 3-phenyl substituent, the indenyl system of indenylidenefluorene dications was less antiaromatic than the fluorenyl system. The decreased antiaromaticity of the 3-phenylindenylidenefluorene dications over the unsubstituted indenylidenefluorene dication was supported by (anti)aromatic (de)stabilization energy calculations, ASE.
制备了对取代的3-苯基茚基芴双阳离子，以研究所得茚基和芴基阳离子体系对反芳香性磁学测量的响应。所有测量方法，即¹H NMR位移、核独立化学位移（NICS(1)(zz)）和磁化率增强值Λ，均支持双阳离子3a - f²⁺的反芳香性。¹H NMR位移和NICS(1)(zz)表明，与茚基单阳离子和芴基单阳离子的反芳香性情况相反，茚基环体系的反芳香性比芴基环体系弱。3位存在苯基取代基能够通过共振稳定亚茚基阳离子，降低其反芳香性，但即使在没有3-苯基取代基的情况下，茚基芴双阳离子的茚基体系的反芳香性也比芴基体系弱。(反)芳香(去)稳定化能量计算（ASE）支持了3-苯基茚基芴双阳离子相对于未取代的茚基芴双阳离子反芳香性降低的情况。
