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Issue 11, 2007
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Evaluating the cyclic π-electron delocalization energy through a double cut of conjugated rings

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Abstract

The cutting of two bonds of a ring AImage ID:b710550a-u1.gifB allows us to define two closed-shell disconnected fragments A and B, and to evaluate the energy of the AImage ID:b710550a-u2.gifB molecule from the eigenstates of A and B by second-order perturbation theory in the framework of tight-binding/Hückel theory. Diagrammatic arguments allow identification of the properly cyclic π-electron delocalization contribution to the energy, which we denote εcyc(AB), and which can be simply expressed in terms of the energies of the cyclic molecule, its fragments and of the two singly bridged Image ID:b710550a-u3.gif and Image ID:b710550a-u4.gif systems. The rules for the selection of suitable A and B fragments are given. The mathematical expression for εcyc(AB) can be translated into a chemical scheme that defines a new energetic aromaticity index, referred to as aromatic cyclic energy (ACE), which may be simply calculated from five Hückel energies. ACE of neutral and ionic [N]annulenes and their ring carbo-mers have been estimated, and shown to yield consistent evaluations of aromatic and antiaromatic cyclic energetic effects. A comparison is made with two other indices of aromaticity, Breslow resonance energies and ELFπ values.

Graphical abstract: Evaluating the cyclic π-electron delocalization energy through a double cut of conjugated rings

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Article information


Submitted
10 Jul 2007
Accepted
18 Sep 2007
First published
12 Oct 2007

New J. Chem., 2007,31, 1918-1927
Article type
Paper

Evaluating the cyclic π-electron delocalization energy through a double cut of conjugated rings

J. Malrieu, C. Lepetit, M. Gicquel, J. Heully, P. W. Fowler and R. Chauvin, New J. Chem., 2007, 31, 1918
DOI: 10.1039/B710550A

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