Homobenzene: homoaromaticity and homoantiaromaticity in cycloheptatrienes.
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