Quantitative Estimate of the Resonance Effects in some Unsaturated, Monocyclic, and Aromatic Hydrocarbons Based on the Renewed Optical Exaltations

2021 ◽  
Vol 25 ◽  
Author(s):  
Boris A. Zaitsev

: The present review discusses a new viewpoint on refractometry as the oldest experimental physical method, whose scientific potential in the estimation of structural effects in organic chemistry has been missed so far. The author demonstrates that upon certain adjustment and redesign of refractometry, this potential can be tapped and successfully used to determine a type of Π-electron interaction, delocalization degree of Π-electrons in organic compounds, and to perform quantitative estimates of resonance effects in unsaturated, (polycyclic) aromatic, and other polyconjugated systems (e.g., fullerenes). The method for accurate separation of molar refraction into additive and constitutive components was suggested; the method is based on the specially developed additive scheme. It was revealed that the negative deviations from additivity for cycloalkanes depend linearly on the number of carbon atoms in the ring. Excellent linear correlations between renewed optical exaltations, the number of Π-electrons in a conjugated system, and experimentally found resonance energy (determined from hydrogenation heat values) were demonstrated. Angular coefficients of the correlation series (ρ-constants) are considered as a criterion of classification, which characterizes the degree of mobility of Π-electrons in the conjugated system of a given type. It is emphasized that the development of methods for precise measurement of the constitutive components of molar refraction may become a useful additional source of information about resonance and other effects in organic and polymer chemistry.

2020 ◽  
Vol 23 (23) ◽  
pp. 2598-2613
Author(s):  
Boris A. Zaitsev

: A retrospective view of exaltation of refraction observed for many unsaturated and aromatic compounds demonstrates that this physical phenomenon is undeservedly considered only as a qualitative measure of conjugation. This mini-review discusses numerous papers by the author that have been published earlier in inaccessible periodicals and collections of scientific papers. Using a great number of illustrations, the author shows that this parameter can be successfully used for quantitative estimate of resonance effects in organic and polymer chemistry. The methods for derivation of strictly additive atomic and group refraction constants are described; these constants were subsequently used as a tool that allowed quantitative estimation of resonance effects in mono-, di-, tri- and polyalkylbenzenes, alkylnaphthalenes, some alkyl derivatives of unsaturated hydrocarbons. These effects cause strictly fixed increase in refraction of carbon atoms in different structural modifications (graphene, fullerene, diamond) and in polycyclic aromatic hydrocarbons. The relevant results regarding quantitative estimation of degree of steric inhibition of resonance in sterically hindered ortho-dialkylbenzenes, 1,2,3- trialkyl-, 1,2,3,4-tetraalkyl-, and 1,2,3,4,5-polyalkylbenzenes accumulated by the author are summarized.


1976 ◽  
Vol 31 (2) ◽  
pp. 115-122 ◽  
Author(s):  
W. Waschkowski ◽  
L. Koester

Rotating activation foils with resonance energies of 1.26 eV and 5.19 eV have been applied for exact measurements of neutron cross sections. The detector consisted of a sandwich of two rotating foils and was suitable for determining exactly the neutron flux at the resonance energy and energy changes in the neutron beam. The cross sections of polycrystalline samples showed uncertainties greater than the statistical error. The more accurate measurements on liquid samples yielded the following scattering cross sections of free atoms for neutrons of zero energy:Lead: σ0(Pb) = (11.261 ±0.006) b,Bismuth: σ0(Bi) = (9.300±0.003) b, andSulfur: σ0(S) = (0.985 ±0.004) b.These data are of interest for an investigation of the neutron-electron interaction.


2009 ◽  
Vol 74 (1) ◽  
pp. 147-166 ◽  
Author(s):  
Robert Ponec ◽  
Stijn Fias ◽  
Sofie Van Damme ◽  
Patrick Bultinck ◽  
Ivan Gutman ◽  
...  

New evidence questioning the multidimensionality of the aromaticity phenomenon exemplified in what is called orthogonality between the classical (structural and energetic) and magnetic aromaticity indices and measures is reported. For this purpose, the recently proposed methodologies for the quantitative characterization of the energy benefits associated with the cyclic arrangement of mobile π-electrons in polycyclic aromatic hydrocarbons are compared with the indices characterizing the extent of cyclic delocalization in the corresponding conjugated circuits. The reported close correlation between both types of indices implies that no discrepancies between classical and magnetic aromaticity measures exist provided the comparison is based on the indices of inherently local nature and/or the interfering contributions of contaminating conjugated circuits is properly taken into account in the description of aromaticity measures like topological resonance energy (TRE) or nucleus independent chemical shift (NICS).


2005 ◽  
Vol 70 (10) ◽  
pp. 1577-1588
Author(s):  
Stanislav Böhm ◽  
Otto Exner

Energies of 39 derivatives of buta-1,3-diene in the twisted conformation were calculated within the framework of the density functional theory at the B3LYP/6-311+G(d,p) level. By comparing with the same molecules in their natural minimum-energy conformations, a scale of resonance effects of various substituents was obtained and expressed in terms of isodesmic reactions. Comparison with other similar scales revealed that this model is not particularly advantageous, its main shortcoming being the relatively small effect. In any case it confirmed that the scales of resonance effects obtained from different models are only very roughly proportional: the classical model of resonance works well in representative examples but has its clear limitation when unduly extended.


2019 ◽  
Vol 97 (5) ◽  
pp. 524-528
Author(s):  
Akbar Ali ◽  
Zafar Iqbal ◽  
Zaffar Iqbal

Predicting physicochemical properties of molecules is one of the fundamental tasks in chemical physics. Many predictive methods have been developed for correlating the molecular structures with their physicochemical properties. One of the simplest such methods involves topological indices. Edge connectivity index (or equivalently, reformulated Randić index), which is denoted as ε, seems to be a good topological index for predicting the solvent accessible molecular volume and molar refraction of polycyclic aromatic hydrocarbons. In this paper, a closed-form formula for calculating the reformulated Randić index ε of benzenoid hydrocarbon chains (or simply, benzenoid chains, which represent a type of polycyclic aromatic hydrocarbons) is derived. Benzenoid chains with maximum (and minimum) ε value are also determined from the collection of all benzenoid chains having fixed number of hexagonal rings. Moreover, an attempt is made to generalize the obtained results for reformulated bond incident degree indices.


1995 ◽  
Vol 49 (6) ◽  
pp. 852-856
Author(s):  
Mudassir M. Husain ◽  
Zahid H. Khan ◽  
Edwin Haselbach

This paper presents some new relations connecting the triplet-state energy of an alternant aromatic hydrocarbon with that of its excited doublet state as well as its first ionization potential. The energy relation between the doublet and triplet states is basically a simplified version of the SDT relation but the predictive power of the proposed correlation is considerably better in spite of the drastic assumptions made in the model. Incorporation of molecular size in the doublet-triplet correlation has no appreciable effect on the predictions, but its inclusion in the ionization potential vs. triplet-state energy relation leads to a significant improvement in the results. It is explained on the basis of our new finding that the Coulomb term appearing in the expression for the ionization potential behaves in the same manner as the molecular size, which thus accounts for electron interaction in the model. The proposed correlations provide a simple but powerful means to estimate the first ionization potentials and excited doublet-state energies of polycyclic aromatic hydrocarbons directly from the knowledge of their triplet-state energies.


Author(s):  
Shuo Li ◽  
Yatao Huang ◽  
Minhui Zhang ◽  
Yanchen Gao ◽  
Canping Pan ◽  
...  

Nitrated polycyclic aromatic hydrocarbons (nPAHs) are ubiquitous environmental pollutants, which exhibits higher toxicity than their corresponding parent PAHs (pPAHs). Recent studies demonstrated that the nPAHs could represent major soil pollution, however the remediation of nPAHs has been rarely reported. In this study, biological, physical, and chemical methods have been applied to remove 1-nitropyrene, the model nPAH, in contaminated soil. A comparative study with pyrene has also been investigated and evaluated. The results suggest that the physical method with activated carbon is an efficient and economical approach, removing 88.1% and 78.0% of 1-nitropyrene and pyrene respectively, within one day. The zero-valent ion has a similar removal performance on 1-nitropyrene (83.1%), converting 1-nitropyrene to 1-aminopyrene in soil via chemical reduction and decreasing the mutagenicity and carcinogenicity of 1-nitropyrene. Biological remediation that employs scallion as a plant model can reduce 55.0% of 1-nitropyrene in soil (from 39.6 to 17.8 μg/kg), while 77.9% of pyrene can be removed by plant. This indicates that nPAHs might be more persistent than corresponding pPAHs in soil. It is anticipated that this study could draw public awareness of nitro-derivatives of pPAHs and provide remediation technologies of carcinogenic nPAHs in soil.


2020 ◽  
Vol 499 (4) ◽  
pp. 6066-6083
Author(s):  
Heidy M Quitián-Lara ◽  
Felipe Fantuzzi ◽  
Ricardo R Oliveira ◽  
Marco A C Nascimento ◽  
Wania Wolff ◽  
...  

ABSTRACT Biphenyl (C12H10), or phenylbenzene, is an important building block of polycyclic aromatic hydrocarbons (PAHs), whose infrared spectral features are present in a variety of galactic and extragalactic sources. In this work, we use synchrotron radiation coupled with time-of-flight spectrometry to study the photoionization and photodissociation processes of biphenyl upon its interaction with soft X-ray photons at energies around the inner-shell C1s resonance. These results are compared with our previous studies with benzene (C6H6) and naphthalene (C10H8), and discussed in the context of four planetary nebulae featuring PAH infrared emission: BD+30○3639, NGC 7027, NGC 5315, and NGC 40. We show that the mass spectrum of biphenyl before the C1s resonance energy is dominated by single photoionization processes leading to C6H$_{5}^+$, C6H$_{4}\, ^{+\cdot}$, and C12H$_{10}\, ^{+\cdot}$, while after the resonance dissociation following multiple photoionization processes is dominant. The release of neutral C6H6 and C6H$_{5}\, ^\cdot$ species accounts for one of the most relevant dissociation processes starting from the doubly ionized biphenyl, indicating that heterolytic charge separation of the two phenyl rings is also achieved. By using quantum chemical calculations, we show that the biphenylic structure is a high-lying isomer of the singly and doubly ionized C12H10 species, whose minimum energy geometries are related to the acenaphthene molecule, composed of a C2-bridged naphthalene. Furthermore, we estimate the lifetime of biphenyl for 275 and 310 eV in photon-dominated regions of planetary nebulae. We discuss distinct processes that may enhance its lifetime and those of other small-sized PAHs in such astrophysical environments.


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