P. Saini, Parul Bhasin, R. Bansal
Aug 1, 2013
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Influential Citations
5
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Journal
Computational and Theoretical Chemistry
Abstract
Abstract A reinvestigation of the homoaromaticity of cyclohepta-1,3,5-triene has been done at the DFT (B3LYP/6-31+G * ) level. The determination of the aromatic stabilization energies based on the hypohomodesmotic reactions gives either too high value (−19.58 kcal mol −1 using ethane as the hydrogen donor molecule) or too low values (−0.46 kcal mol −1 using cycloheptane or −4.27 kcal mol −1 using cyclopentane molecules as the hydrogen donor molecules), as the ring strains on the two sides of the reactions are not compensated. The isomerisation reaction of methylenecyclohepta-1,3-diene to 1-methylcyclohepta-1,3,5-triene gives a value of −10.68 kcal mol −1 as the isomerisation energy. Investigation of the valence tautomerization of cyclohepta-1,3,5-triene to norcaradiene and back to cyclohepta-1,3,5-triene reveals that a dynamic equilibrium exists between the two valence tautomers due to small activation energy barriers, which causes strong interactions between the π orbitals of the triene moiety and the HC CH 2 CH σ orbitals. The NBO analysis of the two valence tautomers and the transition structure involved therein support these interactions. The Frontier Molecular Orbitals of cyclohepta-1,3,5-triene, norcaradiene and the transition structure depict unambiguously the formation of the annular electron cloud, which confers homoaromatic character on cyclohepta-1,3,5-triene.