Huckel theory and aromatically

Schaad, L. J.; Heß, Benjamin

doi:10.1021/ed051p640

Cited by 57 publications

(15 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Finally, the thermochemical, Dewar-type, resonance energy (T RE) is defined as the energy difference between the conjugated monocycle and an appropriate reference system R [59][60][61][62][63]. In the present case R is the hypothetical cyclic hexatriene or cyclic butadiene with the same amount of π-conjugation as in the open-chain polyene, as sketched in Figure 5.…”

Section: Quantum Mechanical and Thermochemical Resonance Energymentioning

confidence: 99%

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Gellini

Salvi

2010

Symmetry

View full text Add to dashboard Cite

The paper introduces general considerations on structural properties of aromatic, antiaromatic and non-aromatic conjugated systems in terms of potential energy along bond length alternation and distortion coordinates, taking as examples benzene, cyclobutadiene and cyclooctatetraene. Pentalene, formally derived from cyclooctatetraene by cross linking, is also considered as a typical antiaromatic system. The main interest is concerned with [n]annulenes and model [n]annulene molecular systems, n ranging from 10 to 18. The rich variety of conformational and configurational isomers and of dynamical processes among them is described. Specific attention is devoted to bridged [10]-and [14]annulenes in the ground and lowest excited states as well as to s-indacene and biphenylene. Experimental data obtained from vibrational and electronic spectroscopies are discussed and compared with ab initio calculation results. Finally, porphyrin, tetraoxaporphyrin dication and diprotonated porphyrin are presented as annulene structures adopting planar/non-planar geometries depending on the steric hindrance in the inner macrocycle ring. Radiative and non-radiative relaxation processes from excited state levels have been observed by means of time-resolved fluorescence and femtosecond transient absorption spectroscopy. A short account is also given of porphycene, the structural isomer of porphyrin, and of porphycene properties.

show abstract

Section: Quantum Mechanical and Thermochemical Resonance Energymentioning

confidence: 99%

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Gellini

Salvi

2010

Symmetry

View full text Add to dashboard Cite

show abstract

“…Therefore, the aromatic stabilization energy (which is based on homodesmotic reaction [4,5]) is often considered the principle criterion for the reactivity of aromatic compounds [6,7]. A number of other stabilization energies reported in the literature to account for this "extra stability" are Hess-Schaad resonance energy [8][9][10][11][12][13], Huckel resonance energy [14][15][16], Schleyer isomerization stabilization energies [17], Dewar resonance energy [18][19][20][21], and topological resonance energies [22][23][24]. Among structural criteria, the Harmonic Oscillator Model of Aromaticity (HOMA) [25][26][27] is a common method for the estimation of aromaticities.…”

Section: Introductionmentioning

confidence: 99%

Aromaticities of Five Membered Heterocycles through Dimethyldihydropyrenes Probe by Magnetic and Geometric Criteria

María¹,

Ayub²

2015

Journal of Chemistry

View full text Add to dashboard Cite

Aromaticities of five membered heterocycles, containing up to three heteroatoms, are quantified through the dimethyldihydropyrene (DHP) probe. Bond fixation caused by the fusion of heterocycles to the dimethyldihydropyrene nucleus (DHPN) was measured by changes in the1H NMR chemical shifts (magnetic) and bond lengths alterations (structural criterion). Chemical shifts of dihydropyrenes were calculated at GIAO HF/6-31G(d)//B3LYP/6-31+G(d). For1H NMR chemical shift analysis, two nonaromatic reference models are studied. Among the studied heterocycles, pyrazole and triazole are about 80–85% aromatic relative to benzene, through both magnetic and geometric criteria. Thiazole and oxazoles are found least aromatic where quantitative estimates of aromaticities are about 34–42%, relative to benzene. These quantitative estimates of aromaticities of five membered heterocycles are also comparable to those from aromatic stabilization energies. The quantification of aromaticity through energetic, magnetic, and structural criteria can deliver the similar inferences provided that suitable reference systems are chosen.

show abstract

“…[1] The aromaticity of a compound may vary considerably depending on the method used for quantitative analysis. Three major categories to quantify aromaticity are energetic, structural and magnetic, essentially all theorectical Dewar resonance energy, [2][3][4][5] Huckel resonance energy, [6][7][8] Hess-Schaad resonance energy, [9][10][11][12][13][14] Schleyer isomerization stabilization energies [15] and topological resonace energies [16][17][18] are a few important energetic criteria. The Harmonic Oscillator Model of Aromaticity (HOMA), [19][20][21] Julg aromaticity index, [22] Bird's aromaticity index [23][24][25][26][27] and Fringuelli structural index [28,29] are the most important structure-based methods for the quantification of aromaticity.…”

Section: Introductionmentioning

confidence: 99%

“…Dewar resonance energy, Huckel resonance energy, Hess‐Schaad resonance energy, Schleyer isomerization stabilization energies and topological resonace energies are a few important energetic criteria. The Harmonic Oscillator Model of Aromaticity (HOMA), Julg aromaticity index, Bird's aromaticity index and Fringuelli structural index are the most important structure‐based methods for the quantification of aromaticity.…”

Section: Introductionmentioning

confidence: 99%

Aromaticities of azines relative to benzene; a theoretical approach through the dimethyldihydropyrene probe

María

Nisa

Hanif

et al. 2014

J. Phys. Org. Chem.

View full text Add to dashboard Cite

The aromaticities of azines relative to benzene have been estimated by fusion with 15,16‐dimethyldihydropyrene. Chemical shift data for the azine‐fused dihydropyrenes (calculated at GIAO HF/6‐31G*//B3LYP/6‐31 + G*) were used to estimate the reduction in the dihydropyrene nucleus aromaticity. Choice of the saturated reference model was quite crucial in reliable estimation of aromaticity. Reference models with partial unsaturation at azine (21,23,25–32) gave better estimate of aromaticity than the parent dimethyldihydropyrene. Aromaticities of azines through chemical shift data and geometric parameter analysis were found to be 90–100% to that of benzene, highly consistent with the aromaticity estimation by nucleus independent chemical shift(0)πzz calculations. Copyright © 2014 John Wiley & Sons, Ltd.

show abstract

Huckel theory and aromatically

Cited by 57 publications

References 9 publications

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Structures of Annulenes and Model Annulene Systems in the Ground and Lowest Excited States

Aromaticities of Five Membered Heterocycles through Dimethyldihydropyrenes Probe by Magnetic and Geometric Criteria

Aromaticities of azines relative to benzene; a theoretical approach through the dimethyldihydropyrene probe

Contact Info

Product

Resources

About