Harmonic oscillator model of aromaticity index

HOMA index (. Harmonic Oscillator Model of Aromaticity index)... 

TABLE 4.15 The Training (Calibration) and Test (Marked With Asterisk - to be chosen) Compounds Studied Along Their HOMA (Harmonic Oscillator Model of Aromatic) Index (Mosquera et al., 2007 Ciesielski et al., 2009) and of Associated Computed (Hypercube, 2002 (Semiempirical, AMI, Polak-Ribier optimization procedure)) Structural First, Second, and Third Order HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) Reactivity Indices (Tarko Putz, 2010)... 

The aromaticity of 1,2,4-triazoles has been investigated and quantified using the harmonic oscillator model of aromaticity (HOMA) index, where a value of 1 is assigned to a molecule that is fully aromatic, 0 for a nonaromatic molecule, and a negative value for a molecule that is antiaromatic the data obtained were compared to other small-molecule heteroaromatics. It was determined that different tautomers of substituted and unsubstitued 1,2,4-triazoles have individual HOMA indices <2000JST(524)151>. 

In a more recent study, the problem of n delocalization in porphyrins and metalloporphyrins was reinvestigated using two different aromaticity indexes, HOMA andNICS [37], The harmonic oscillator model of aromaticity (HOMA) [31] quantifies the aromaticity of a system on the basis of the calculated deviation of its... 

A theoretical evaluation of the aromaticity of the pyrones pyromeconic acid, maltol, and ethylmaltol along with their anions and cations was carried out at several levels (Hartree-Fock, SVWN, B3LYP, and B1LYP) using the 6-311++G(d,p) basis set <2005JP0250>. The relative aromaticity of these compounds was evaluated by harmonic oscillator model of aromaticity (HOMA), nucleus-independent chemical shifts (NICSs), and /6 indexes and decreases in the order cation > neutral molecule > anion. 

Harmonic oscillator model of aromaticity (HOMA) — This is a geometry-based index of aromaticity that takes into account two effects. These are the increase in bond-length alternation (GEO term) and the increase in mean bond length in the system (EN term) such that HOMA= 1-EN-GEO <2004PCP249>. For examples see Sections 2.2.42.3, 2.3.42.3, and 244.2.3. 

The harmonic oscillator model of aromaticity (HOMA) index and Bird aromaticity indices (/5,15 6, and /A) for selected heterocycles are shown in Table 35 and Figure 15. The theoretical background to these indices is discussed in Section 2.2.4.2.3. To facilitate direct comparison between ring systems, Bird introduced a unified aromaticity index /A that is related to the indices for five- and six-membered rings and fused rings by the expression ... 

Polarizability anisotropy of the 7t-electrons is regarded as the best available polarizability-based aromaticity index from a comparison of Pozharskii s index AA, Bird s index /a, the harmonic oscillator model of aromaticity (HOMA) index, the parallel polarizability a, the polarizability anisotropy, and the 7t-electron counterparts a < and Aa" <2004MI427>. 

Several reviews on various aspects of oxazole chemistry have been published. Cicchi and co-workers and Gilchrist reviewed synthesis and reactions of oxazoles. Walsh and co-workers " reviewed the biosynthesis of thizazole and oxazole peptides, including microcin B17 1196. Kawase and co-workers reviewed the synthesis of 5-(trifluoromethyl)oxazoles via Dakin-West chemistry. Suga and Ibata reviewed much of their work on [3 - - 2] cycloadditions of 5-alkoxyoxazoles. In addition, Mrozek and co-workers applied the harmonic oscillator model of aromaticity (HOMA) index to live-membered ring heterocycles, including oxazoles. 

Figure 1 Correlations between HOMA aromaticity index and resonance substituent constant (cjr) for substituted benzene (Bz), pyrazole (Pz), and imidazole (Im) derivatives. HOMA, harmonic oscillator model of aromaticity. Reprinted with permission from (20nJPCA(ii 5)8571). Copyright 2011 American Chemicai Society.

Scheme 3 Effects of fusion and substituents on aromaticity of nucleobases red numbers—HOMA index. HOMA, harmonic oscillator model of aromaticity.

Krygowski 5 harmonic oscillator model of aromaticity (HOMA) as structural index of aromaticity S... 

Krygowski et al defined the Harmonic Oscillator Model Of Aromaticity (HOMA) index as. 

On the basis of geometrical considerations, molecules should show a decrease in aromatic character when they possess a high degree of bond alternation and deviate significantly from planarity. Several quantitative measures of this bond alternation have been proposed. Among the most important ones, we mention the Julg aromaticity index and the harmonic oscillator model of aromaticity (HOMA). " ... 

In addition to the above prescriptions, many other quantities such as solution phase ionization potentials (IPs) [15], nuclear magnetic resonance (NMR) chemical shifts and IR absorption frequencies [16-18], charge decompositions [19], lowest unoccupied molecular orbital (LUMO) energies [20-23], IPs [24], redox potentials [25], high-performance liquid chromatography (HPLC) [26], solid-state syntheses [27], Ke values [28], isoelectrophilic windows [29], and the harmonic oscillator models of the aromaticity (HOMA) index [30], have been proposed in the literature to understand the electrophilic and nucleophilic characteristics of chemical systems. 

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