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1.
Phys Chem Chem Phys ; 15(9): 3286-93, 2013 Mar 07.
Article in English | MEDLINE | ID: mdl-23358331

ABSTRACT

The ring-current aromaticity of the bicalicene molecule arises, in spite of the 16 π carbon perimeter, from strong local diatropic circulations on the two pentagonal rings, as shown by current-density maps computed at the ipsocentric RHF/6-311G** and DFT/6-311G** levels of theory. Conjugated-circuit models cannot capture this pattern of circulation as it arises from 'ionic' contributions in a valence-bond picture. Canonical molecular-orbital analysis reveals a cancellation of paratropic and diatropic frontier-orbital contributions, which explains the difficulties that Hückel-based models have in producing qualitatively correct current-density maps for this molecule. Other measures of aromaticity reflect, to different extents, the dominance of the 'tetraionic' contribution to the aromaticity of this species.


Subject(s)
Hydrocarbons, Aromatic/chemistry , Polycyclic Compounds/chemistry , Quantum Theory , Models, Molecular , Molecular Conformation
2.
Org Lett ; 12(21): 4880-3, 2010 Nov 05.
Article in English | MEDLINE | ID: mdl-20873865

ABSTRACT

At the B3LYP/6-311++G(d,p) level, approach of a lithium atom to a face of the fulvene molecule leads to formation of a complex with binding energy 41 kcal/mol and significant ion-pair character. The fulvene moiety gains a delocalized aromatic cyclic π system, documented by the geometry-based aromaticity index HOMA, and a strong diatropic ring current, visualized by ipsocentric calculation of the π current-density, which leads to an "aromatic" NICS value of -11 ppm.


Subject(s)
Cyclopentanes/chemistry , Lithium/chemistry , Models, Molecular , Molecular Conformation
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