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Homobenzene: homoaromaticity and homoantiaromaticity in cycloheptatrienes.
Chen, Zhongfang; Jiao, Haijun; Wu, Judy I; Herges, Rainer; Zhang, S B; Schleyer, Paul von Ragué.
Affiliation
  • Chen Z; Department of Chemistry, Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, PR. zhongfangchen@gmail.com
J Phys Chem A ; 112(42): 10586-94, 2008 Oct 23.
Article in En | MEDLINE | ID: mdl-18826196
Cycloheptatriene (C(s)) is firmly established to be a neutral homoaromatic molecule based on detailed analyses of geometric, energetic, and magnetic criteria. Substituents at the 7 (methylene) position, ranging from the electropositive BH2 to the electronegative F, favor the equatorial conformation but influence the aromaticity only to a small extent. By the same criteria, the planar transition state (C(2v)) for cycloheptatriene ring inversion is clearly antiaromatic. This is attributed to the involvement of the pseudo-2pi-electrons of the CH2 group with the 6pi-electrons of the ring to give an 8pi-electron system. Similarly, the participation of the CH2 groups into C(2v) cyclopentadiene and cyclononatetraene lead to significant 4n + 2 pi electron aromaticity. The cyclization of cycloheptatriene to norcaradiene proceeds via a highly aromatic transition structure, but norcaradiene itself is less aromatic than cycloheptatriene. An annelated cyclopropane ring does not function as effectively as a double bond in promoting cyclic electron delocalization.

Full text: 1 Collection: 01-internacional Database: MEDLINE Language: En Journal: J Phys Chem A Journal subject: QUIMICA Year: 2008 Document type: Article Country of publication: United States

Full text: 1 Collection: 01-internacional Database: MEDLINE Language: En Journal: J Phys Chem A Journal subject: QUIMICA Year: 2008 Document type: Article Country of publication: United States