What does the HOMA index really measure?

Ostrowski, Sławomir; Dobrowolski, Jan Cz.

doi:10.1039/c4ra06652a

Cited by 63 publications

(71 citation statements)

References 21 publications

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“…The Harmonic Oscillator Model of Aromaticity (HOMA) index was used to evalute the aromaticity of the molecules from the geometrical aspect . The HOMA indices were calculated using the following equation

HOMA = 1 - \frac{α}{n} \sum_{i = 1}^{n} false(R_{i} - {R_{opt})}^{2}

where, R i is i th CC bond length in the ring of the analyzed molecule and the CC bond length of benzene (1.388 Ǻ) was used as R opt .…”

Section: Computational Detailsmentioning

confidence: 99%

Design of neutral organic superacids using fulvene derivatives with di-enol substituent

Valadbeigi

2016

Int. J. Quantum Chem.

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A new class of superacids was designed using enolic derivatives of fulvene. After deprotonation, bond rearrangement leads in a stable conjugate base with an aromatic cyclopentadienyl ring and a carboxyl group. The gas phase enthalpies ( ΔHacid°) of the deprotonation, as an index of acidity, were calculated employing the B3LYP method and 6‐311++G(d,p) and aug‐cc‐PVDZ basis sets. The acidity of these compounds without any electron withdrawing groups was more than H2SO4 in gas phase. The acidity increased by substituting electron withdrawing groups (F, CN, and O) into the molecules so that we could achieve a cyano derivative of fulvene with ΔHacid° = 250 kcal/mol.

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HOMA = 1 - \frac{α}{n} \sum_{i = 1}^{n} false(R_{i} - {R_{opt})}^{2}

where, R i is i th CC bond length in the ring of the analyzed molecule and the CC bond length of benzene (1.388 Ǻ) was used as R opt .…”

Section: Computational Detailsmentioning

confidence: 99%

Design of neutral organic superacids using fulvene derivatives with di-enol substituent

Valadbeigi

2016

Int. J. Quantum Chem.

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“…The multidimensional aspect of aromaticity has been discussed in the literature using several criteria, including energetic and geometric ones. The latter one was proposed by Krygowski and co‐workers and called harmonic oscillator model of aromaticity (HOMA).…”

Section: Introductionmentioning

confidence: 99%

Method and basis set dependence of the NICS indexes of aromaticity for benzene

Gajda

Kupka

Broda

et al. 2018

Magnetic Reson in Chemistry

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The role of theory level in prediction of benzene magnetic indexes of aromaticity is analysed and compared with calculated nuclear magnetic shieldings of He used as NMR probe. Three closely related nucleus-independent chemical shift (NICS) based indexes were calculated for benzene at SCF-HF, MP2, and DFT levels of theory and the impact of basis set on these quantities was studied. The changes of benzene NICS(0), NICS(1), and NICS(1)zz parameters calculated using SCF-HF, MP2 and several density functionals were within 1 to 3 ppm. Similar deviations between magnetic indexes of aromaticity were observed for values calculated with selected basis sets. Only very small effect of polar solvent on benzene aromaticity was predicted. The He nuclear magnetic isotropic shielding (σ) and its zz-components (σ ) of helium atom approaching the centre of benzene ring from above produced similar curves versus benzene-He distance to NICS parameters calculated for similarly moving Bq ghost atom. We also propose an experimental verification of NICS calculations by designing the He NMR measurement for benzene saturated with helium gas or in low temperature matrices.

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“…A molecular system satisfying specific energetic, geometric, magnetic, and chemical reactivity criteria could be called aromatic [45,46,[49][50][51][52][53][54]. Obviously, aromaticity is one of the most frequently used concepts in chemistry.…”

Section: Introductionmentioning

confidence: 99%

“…However, unlike chemical bonding, aromaticity is a multidimensional property. Therefore, in common practice are aromaticity studies including results obtained from various criteria [45,46,[49][50][51][52][53][54] and recently concentrating on two popular aromaticity indexes: HOMA [45,46,52] and NICS [47,49]. Thus, these parameters should reflect geometrical (HOMA) and magnetic (NICS) properties of three different ring subunits of phthalocyanine (see Fig.…”

Section: Introductionmentioning

confidence: 99%

Solvent impact on the planarity and aromaticity of free and monohydrated zinc phthalocyanine: a theoretical study

2017

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A theoretical investigation on the planarity of molecular structure of zinc phthalocyanine (ZnPc) and its aromaticity has been performed using B3LYP and M06-2X density functionals combined with selected Pople-type basis sets. The effect of the applied calculation method on the optimized structure of ZnPc and ZnPc•••H 2 O, both in the gas phase and in the polar solvent, was analyzed. To quantify the aromaticity of the ZnPc and ZnPc•••H 2 O complexes, both the geometric and magnetic criteria, i.e., Harmonic Oscillator Model of Aromaticity (HOMA) index and the nucleus-independent chemical shift (NICS) values at the centers or 1 Å above the centers of structural subunits, were calculated. The energies of highest energy occupied molecular orbital (HOMO) and lowest energy unoccupied molecular orbital (LUMO) and energy gaps were also estimated. The results show that the free ZnPC molecule is flat in the gas phase and nonplanar in the polar environments (DMSO and water). ZnPC•••H 2 O is nonpolar in the gas phase and polar solvent which is in agreement with recent X-ray reports. Both HOMA and NICS indexes indicate the presence of highly aromatic macrocycle and benzene rings while these parameters for pyrrolic ring are significantly smaller than in free pyrrole. The presence of polar solvents practically does not change aromaticity of the ring subunits of the studied compounds.

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What does the HOMA index really measure?

Abstract: The HOMA index reflects a more general property of cyclic hydrocarbons then aromaticity: the savoricity.

Cited by 63 publications

References 21 publications

Design of neutral organic superacids using fulvene derivatives with di-enol substituent

Design of neutral organic superacids using fulvene derivatives with di-enol substituent

Method and basis set dependence of the NICS indexes of aromaticity for benzene

Solvent impact on the planarity and aromaticity of free and monohydrated zinc phthalocyanine: a theoretical study

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