An electronic properties investigation to interpret the substituent constants of monosubstituted benzene derivatives

Advanced oxidation processes for the removal of mono and polycyclic aromatic hydrocarbons - A review

Aromatic hydrocarbons (AHs) are toxic environmental contaminants presented in most of the environmental matrices. Advanced oxidation processes (AOPs) for the removal of AHs in the account of complete mineralization from various environmental matrices have been reviewed in this paper. An in-depth discussion on various AOPs for mono (BTEX) and polyaromatic hydrocarbons (PAHs) and their derivatives is presented. Most of the AOPs were effective in the removal of AHs from the aquatic environment. A comparative study on the degradation of various AHs revealed that the oxidation of the AHs is strongly dependent on the number of aromatic rings and the functional groups attached to the ring. The formation of halogenated and nitrated derivatives of AHs in the real contaminated water containing chloride, nitrite, and nitrate ions seems to be a challenge in using the AOPs in real systems. The phenolic compounds, quinone, alcohols, and aliphatic acids are the important byproducts formed during the oxidation of AHs, initiated by the attack of reactive oxygen species (ROS) on their electron-rich center. In conclusion, AOPs are the adaptable method for the removal of AHs from different environmental matrices. The persulfate-based AOPs were applied in the soil phase removal as an in situ chemical oxidation of AHs. Moreover, the combination of AOPs will be a conclusive solution to avoid or minimize unexpected or other toxic intermediate products and to obtain rapid oxidation of AHs.

The structure-activity relationship of aromatic compounds in advanced oxidation processes：a review

Advanced oxidation processes (AOPs) are widely used as efficient technologies to treat highly toxic and harmful substances in wastewater. Taking the most representative aromatic compounds (monosubstituted benzenes, substituted phenols and heterocyclic compounds) as examples, this paper firstly introduces their structures and the structural descriptors studied in AOPs before, and the influence of structural differences in AOPs with different reactive oxygen species (ROS) on the degradation rate was discussed in detail. The structure-activity relationship of pollutants has been previously analyzed through quantitative structure-activity relationship (QSAR) model, in which ROS is a very important influencing factor. When electrophilic oxidative species attacks pollutants, aromatic compounds with electron donating groups are more favorable for degradation than aromatic compounds with electron donating groups. While nucleophilic oxidative species comes to the opposite conclusion. The choice of advanced oxidation processes, the synergistic effect of various active oxygen species and the used catalysts will also change the degradation mechanism. This makes the structure-dependent activity relationship uncertain, and different conclusions are obtained under the influence of various experimental factors.

Valence non-Lewis density as an approach to describe and measure aromaticity of organic and inorganic molecules

Based on the linear combination of atomic orbital-molecular orbital by the natural bond orbitals (NBO) theory, the attractive donor-acceptor superposition interaction between filled (Lewis-type) and vacant (non-Lewis-type) orbitals provide a general mechanism for quantal energy lowering. This interaction has a direct impact on the quantity of the second-order stabilization energy. Therefore, the valence non-Lewis density (VNLD) index, the electron density of unoccupied valence nonbonding and antibonding orbitals, is introduced as an approach to describe and measure aromaticity. This index is based on the frontier orbital concept. To investigate the validity of the proposed aromaticity index, we selected several test sets of organic and inorganic molecules such as different ring sizes in cyclic and heterocyclic hydrocarbons, and all-metal and semimetal clusters, and compared our findings with previous aromaticity analysis. According to the results, VNLD values are well correlated and anticipated the order of aromaticity with the formerly introduced criteria. Furthermore, VNLD reveals that the rings with π-sextet electrons localized in a ring are more aromatic than the other rings, thus, it is in line with Clar's rule. Our proposed aromaticity index has advantages such as, easy to obtain from NBO analysis, and does not require reference molecules which made it more applicable for realizing the aromaticity order in many organic and inorganic compounds.

On the aromaticity of uracil and its 5-halogeno derivatives as revealed by theoretically derived geometric and magnetic indexes

The problem of aromaticity in heterocyclic rings of uracil and its 5-halogenoderivatives (5XU) was analyzed theoretically by calculating modified harmonic oscillator model of aromaticity (HOMA) for Heterocycle Electron Delocalization (HOMHED), nucleus-independent chemical shift parameters (NICS) and the so-called scan experiments, using helium-3 atom as a magnetic probe. The impact of halogen electronegativity on C5 atom’s NBO charges was also investigated. Water, as a polar environment, has a negligible impact on 5XU aromaticity. The most stable diketo tautomer shows a very low aromaticity while the “rare” dihydroxy form (tautomer No 6) is aromatic and resembles benzene. This is in agreement with traditional drawing of chemical formula of uracil’s six-membered ring, directly showing three alternating single and double bonds in its tautomer No 6. No good correlation between magnetic and geometric indexes of aromaticity for the studied 5XU tautomers was found. Linear correlation between the magnitude of NICS minimum, as well as the distance of the minimum above uracil ring plane center from 3He NMR chemical shift scan plot with respect to halogen electronegativity were observed. A strong linear dependence of magnetic index of aromaticity and the electronegativity of 5X substituent was observed.

Total non-lewis structures: An application to predict the stability and reactivity of linear and angular polyacenes

In the present work, the total non-Lewis structure (TNLS) is introduced for describing the stability and reactivity of linear and angular polyacenes. TNLS of a molecule is derived from the natural bond orbital theory representing the antibonding orbitals and/or electron delocalization of π^∗ orbitals. To verify this application, we obtained the TNLS values of thirteen linear and angular polyacenes and evaluated with other quantitative aromaticity probes based on reactivities, energetics, geometrics, and magnetic properties. Our results show that there is a remarkable second-order polynomial correlation between TNLS and seven popular global measures of aromaticity including hardness, resonance energy, aromatic stabilization energy, harmonic oscillator measure of aromaticity, magnetic susceptibility exaltation, global magnetic characteristics, and mean polarizability. By increasing the TNLS values of the systems the reactivity increases and stability decreases. It is worth mentioning that the angular polyacenes produce less TNLS values than the linear systems with the same number of benzene rings. Therefore, it can be stated that TNLS values confirmed with Clar's rule which in general prove the angular polyacenes are more stable than linear ones.