Aromaticity and Homoaromaticity in Methano[10]annulenes

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• 作者：Giovanni F. Caramori ; Kleber T. de Oliveira ; S&eacute ; rgio E. Galembeck ; Patrick Bultinck ; Mauricio G. Constantino
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：January 5, 2007
• 年：2007
• 卷：72
• 期：1
• 页码：76 - 85
• 全文大小：291K
• 年卷期：v.72,no.1(January 5, 2007)
• ISSN：1520-6904

文摘

Aromaticity and neutral homoaromaticity have been evaluated in methano[10]annulenes systems, 1,4-methano[10]annulene (1), 1,5-methano[10]annulene (2), and 1,6-methano[10]annulene (3). C-C bondlengths indicate that 1 presents higher bond alternation than 2 and 3. The relative energies were determinedat the B3LYP/6-311+G(d,p) level, and they pointed out that 3 is the most stable isomer. Strain energies,evaluated employing homodesmotic reactions, show the same order as the relative energies. Through adecomposition of strain energies, it could be concluded that the rings absorb more tension than the bridges.The changes in aromaticity were evaluated by magnetic susceptibilities, _M, HOMA, NICS, and resonanceenergies, RE. HOMA, RE, and _M indicate that 2 and 3 are strongly, and 1 is fairly, aromatic. NICS doesnot provide reliable results, due to interference of ring and bridge atoms. NBO analysis presents someinteractions that suggest the existence of neutral homoaromaticity. GPA indices (evaluated at the B3LYP/6-31G* level) point out that homoaromaticity plays a relevant role only in 3. Moreover, this work is thefirst in the current literature that studies 1,4-methano[10]annulene (1).