Multicenter bond indices

An MO multicenter bond index involving the cr + 7t electron population is proposed as a measure of aromaticity. It is related both to the energetic and to the magnetic criteria <2000PGP3381>. 

This index, an invariant in the tensor sense <1984ZNA1259>, gives the electronic population along the AB bond and gives values agreeing with chemical expectation. The multicenter bond index <1990STG423>, an extension of /ab to multicenter bonds, involves the total electron population (despite admitting ct-rt-separation). 

MO multicenter bond index (/ring) involving the a+n electron population (this index is related both to energetic and magnetic criteria) <2000PCP3381> ... 

An MO multicenter bond index involving a- and 7t-electron population is related to both energetic and magnetic criteria. Since aromaticity is certainly related to the mutual simultaneous interaction of all bonds of an aromatic ring, 7,ing is defined as a measure of aromaticity <2000PCP3381>. 7, ng values for 1, 1,2,4- and 1,3,5-triazine are 0.087 5,... 

To define Kab and more general multicenter indices at a post Hartree-Fock level, one must invoke more sophisticated techniques [64-67]. We follow our work [36] in which the full Cl and some approximated models were considered in detail. The conventional definition of the generalized bond index is based on identification of Kab with a charge density fluctuation measured via the second-order joint statistical moment [64] (generally, the joint cumulant) ... 

The amount of electron delocalization has been considered to be a measure of aromaticity. There exist several related aromaticity indices. Giambiagj and coworkers have shown a connection between aromaticity and a multicentre bond index. Bultinck et al7 have used the following multicenter index (MCI) for this purpose,... 

The use of multicenter bond indices as a measure of aromaticity was initially proposed by Giambiagi et al. [95]. These indices measure the extension of the electron delocalization to all centers of the ring which is expected to be large for aromatic systems. Bultinck et al. [96] employed the multicenter bond indices computed from Mulliken-type calculation as a measure of local aromaticity in polyatomic hydrocarbon. Thus, the n-center delocalization index, (A ) can be compnted in the framework of quantum theory of atoms in molecules (QTAIM). 

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