On the HOMA index of some acyclic and conducting systems

Dobrowolski, Jan Cz.; Ostrowski, Sławomir

doi:10.1039/c4ra15311a

Cited by 26 publications

(37 citation statements)

References 22 publications

(28 reference statements)

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“…In HOMED(0), the bond lengths of ethane and ethene were taken for the C-C and C=C bonds in the Kekulé structure of benzene, whereas those of 1,3-butadiene were used for the hypothetical structure of benzene in HOMA(0). These differences in the reference bond lengths lead to the negative HOMA values for hydrocarbons being less delocalized than the structure taken for HOMA(0) [55,56]. On the other hand, both HOMED and HOMA are equal to zero for the Kekulé structure of s-triazine with non-delocalized C-N and C=N bonds.…”

Section: Conceptual Approaches and Computational Methodsmentioning

confidence: 95%

Push–Pull Effect on the Gas-Phase Basicity of Nitriles: Transmission of the Resonance Effects by Methylenecyclopropene and Cyclopropenimine π-Systems Substituted by Two Identical Strong Electron Donors

et al. 2021

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The gas-phase basicity of nitriles can be enhanced by a push–pull effect. The role of the intercalated scaffold between the pushing group (electron-donor) and the pulling (electron-acceptor) nitrile group is crucial in the basicity enhancement, simultaneously having a transmission function and an intrinsic contribution to the basicity. In this study, we examine the methylenecyclopropene and the N-analog, cyclopropenimine, as the smallest cyclic π systems that can be considered for resonance propagation in a push–pull system, as well as their derivatives possessing two strong pushing groups (X) attached symmetrically to the cyclopropene scaffold. For basicity and push–pull effect investigations, we apply theoretical methods (DFT and G2). The effects of geometrical and rotational isomerism on the basicity are explored. We establish that the protonation of the cyano group is always favored. The push–pull effect of strong electron donor X substituents is very similar and the two π-systems appear to be good relays for this effect. The effects of groups in the two cyclopropene series are found to be proportional to the effects in the directly substituted nitrile series X–C≡N. In parallel to the basicity, changes in electron delocalization caused by protonation are also assessed on the basis of aromaticity indices. The calculated proton affinities of the nitrile series reported in this study enrich the gas-phase basicity scale of nitriles to around 1000 kJ mol−1.

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Section: Conceptual Approaches and Computational Methodsmentioning

confidence: 95%

Push–Pull Effect on the Gas-Phase Basicity of Nitriles: Transmission of the Resonance Effects by Methylenecyclopropene and Cyclopropenimine π-Systems Substituted by Two Identical Strong Electron Donors

et al. 2021

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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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On the HOMA index of some acyclic and conducting systems

Abstract: The HOMA index can be useful for acyclic linear systems and design of new conducting polymers.

Cited by 26 publications

References 22 publications

Push–Pull Effect on the Gas-Phase Basicity of Nitriles: Transmission of the Resonance Effects by Methylenecyclopropene and Cyclopropenimine π-Systems Substituted by Two Identical Strong Electron Donors

Push–Pull Effect on the Gas-Phase Basicity of Nitriles: Transmission of the Resonance Effects by Methylenecyclopropene and Cyclopropenimine π-Systems Substituted by Two Identical Strong Electron Donors

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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