Substituted Benzenes Research Articles

π-Stacking effects on acid capacity of p-aminobenzoic acid

Acidity changes of p-aminobenzoic acid (pABA) after π-stacking with substituted benzenes (SB) have been investigated using quantum mechanical calculations at the M06-2X/6-311++G(d,p) level of theory. In addition to benzene derivatives that are usually used as a model for aromatic amino acids (AA), two amino acids, tryptophan (TRP) and histidine (HIS), with different cyclic structures were also considered in this work. All substituents enhance the stacking interactions, in which enhancement is higher for electron-withdrawing substituents (EWSs). The stacking interaction (in presence of all substituents) enhances the acidity (3.42 for Br). Natural energy decomposition analysis (NEDA) shows that the polarization interactions (POL) have the largest contribution in the binding energies (ΔE) of neutral and anionic complexes, while the electrostatic effects (ES) are in better correlation with ΔE. The ΔE values are linearly dependent on the sum of electron densities (ΣρBCP) calculated at the bond critical points (BCPs) between the rings and the ΣρRCP values calculated at the ring critical points (RCPs) in the neutral and anionic SB||pABA complexes. An excellent correlation was found between the ΔE values and a combination of electrostatic (σmeta), resonance/induction (σpara), and dispersion/polarizability (molar refractivity, MR) substituent constant terms. There are good relationships between pKa and the global minimum and maximum of electrostatic potential around the O (∑Vmin-O) and H (Vmax-H) atoms, and the results of natural population analysis (NPA). Therefore, the electrostatic and charge transfer effects play a major role in acidity.

Preparation, characterization, and performance evaluation of UiO-66 analogues as stationary phase in HPLC for the separation of substituted benzenes and polycyclic aromatic hydrocarbons.

UiO-66 analogues are good candidates as stationary phase in HPLC because of their chemical/thermal stability, large surface area, and two cage structures. Here, two UiO-66 analogues, UiO-66-NH2 and UiO-67, were synthesized and used as stationary phase in HPLC to evaluate their performance in the separation of substituted benzenes (SBs) and polycyclic aromatic hydrocarbons (PAHs). The results showed that SBs could be well separated on UiO-66-NH2 column but not on UiO-67 column. Nonetheless, PAHs could be well separated on UiO-67 column. The separation mechanisms of SBs and PAHs on UiO-66 analogues may be involved in the pore size and functional group in the frameworks of UiO-66 analogues. Introduction of the–NH2 into UiO-66 significantly reduced its adsorption capacity for SB congeners, which resulted in less separation of SBs on UiO-66-NH2. As for the separation of PAHs on UiO-67 column, the π-π stacking effect was supposed to play a vital role.

Strongly Directing Substituents in the Radical Arylation of Substituted Benzenes.

Although general interest in radical arylation reactions has grown rapidly in recent years, poor regioselectivities and the need to use a large excess of the radical-accepting arene have hindered their application to substituted benzenes. We now describe experimental and computational investigations into the substituent effects that lead to regioselective addition based on the recent discovery of anilines as outstanding substrates for radical arylations.

ChemInform Abstract: Novel [4 + 2]‐Benzannulation to Access Substituted Benzenes and Polycyclic Aromatic and Benzene‐Fused Heteroaromatic Compounds.

A common [4 + 2]-benzannulation of Morita–Baylis–Hillman acetates of acetylenic aldehydes with boronic acids has been developed for the synthesis of aromatic and heteroaromatic compounds through tandem allylic substitution/hydroarylative cycloisomerization process. This method provides a facile and general route to substituted benzenes, naphthalenes, other polycyclic aromatics, and various benzene-fused heteroaromatic compounds such as benzofuran, benzothiophene, indole, and carbazoles.

Nanoclustered Gold: A Promising Green Catalysts for the Oxidation of Alkyl Substituted Benzenes

Catalytic oxidation of alkyl substituted benzenes is an essential route for the synthesis of a number of important chemicals, perfumes, drugs and pharmaceuticals. The oxidation products of ethyl benzene are important precursors for a wide range of pharmaceuticals and synthetic materials. Acetophenone and 1-phenylethanol are two oxidation products of ethyl benzene which are the precursors of optically active alcohol, benzalacetophanones, hydrazones and so on. However, the oxidations of alkyl substituted benzenes have been remaining a challenging task. This is because of the limitations of an appropriate catalyst and requirement of corrosive chemical treatments (potassium permanganate/dichromate and ammonium cerium nitrate) which are hazardous and environmentally unfriendly. The current industrial practice in the oxidation of ethyl benzene unfortunately involves high temperature thermal autoxidation in the absence of catalysts. Although few catalysts have been tested for the oxidation of ethyl benzene, many of them found to be inefficient. For example, cobalt (II) oxide-immobilized on mesoporous silica (Co/SBA-15) was used to catalyze oxidation of alkyl benzene at high temperature (125-150°C) but only 70% conversion was obtained after prolong treatment at 150°C. Additionally, the catalyst formed mixed uncontrolled oxidation products like 1-phenylethyl hydro peroxide, benzoic acid, acetophenone and phenyl ethanol. Carbon/silica/metal oxide supported nanoporous gold is a promising green catalyst for heterogenous molecular transformation. This is because of their three dimensional open pore network structures, high surface to volume ratio, high reusability, distinct optolectronic and physio-chemical properties. Mesoporous carbon/silica/metal oxide thin film supports provide increase dispersion of metal nanocatalysts and facilitate transport of molecules, ions or electrons through the nanopores/nanochannels, enhancing product yields with minimum cost and time. This paper has reviewed various gold-skeleton green catalysts and their preparation and mechanistic schemes for the selective oxidation of alkyl substituted benzenes.

Fluorescent Selective Chemosensor for Fluoride Ion with Pyrene Based on Triphenylphosphine

An effective fluorescencechemosensor must convert the event of anion recognition bythe ionophore into an easily monitored and highly sensitivelight signal from the fluorophore. Fluorescent moieties avail-able to the scientist are typically aromatics such as sub-stituted benzenes, anthracenes, naphthalenes, and pyrenes.Pyrenes are a particularly elegant basis for ratiometric basedoptical sensors, where the ra tio of two emission wavelengthscomprised the analytical signal. To date the pyrene excimer/monomer system has been exploited mainly for cationsensingand increasingly for anion sensing.

ChemInform Abstract: Facile and Controllable Synthesis of Multiply Substituted Benzenes via a Formal [3 + 3] Cycloaddition Approach.

AbstractAn efficient protocol for preparation of di‐ to pentasubstituted benzene derivatives from α,β‐unsaturated carbonyl derivatives and ylides is presented.

Synthesis and Reactions of Enantiopure Substituted Benzene cis-Hexahydro-1,2-diols

Enantiopure cis-dihydro-1,2-diol metabolites, obtained from toluene dioxygenase-catalysed cis-dihydroxylation of six monosubstituted benzene substrates, have been converted to their corresponding cis-hexahydro-1,2-diol derivatives by catalytic hydrogenation via their cis-tetrahydro-1,2-diol intermediates. Optimal reaction conditions for total catalytic hydrogenation of the cis-dihydro-1,2-diols have been established using six heterogeneous catalysts. The relative and absolute configurations of the resulting benzene cis-hexahydro-1,2-diol products have been unequivocally established by X-ray crystallography and NMR spectroscopy. Methods have been developed to obtain enantiopure cis-hexahydro-1,2-diol diastereoisomers, to desymmetrise a meso-cis-hexahydro-1,2-diol and to synthesise 2-substituted cyclohexanols. The potential of these enantiopure cyclohexanols as chiral reagents was briefly evaluated through their application in the synthesis of two enantiomerically enriched phosphine oxides from the corresponding racemic phosphine precursors.

Substituent Effects in Sandwich Configurations of Multiply Substituted Benzene Dimers Are Not Solely Governed By Electrostatic Control

Noncovalent interactions between pi systems are central to understanding protein folding and the stability of DNA. Considerable controversy exists about whether substituent effects in pi-pi interactions can be understood purely on the basis of electrostatic interactions or whether other effects must be included to understand observed trends. In this work, we show that in general, pi-pi interactions are not governed solely by electrostatic control. We do not observe a linear correlation between the relative interaction energies and the sums of Hammett parameters in the case of multiply substituted face-to-face benzene dimers. Instead, differential dispersion effects can be so large that even molecules with wildly different electrostatic potentials can exhibit similar attractions to benzene.

Calculations on the Group 15 Intraring Substituted Benzenes (Pyridine to Bismin Series) and Their Datively Bonded Oxides and Sulfides

The series of heterocyclic compounds pyridine, phosphorin, arsenin, antimonin, bismin, and the related series of pyridine oxide, etc., and pyridine sulfide, etc., were investigated using density functional theory. In addition to molecular geometries and energies, the nucleus independent chemical shift (NICS) values were calculated for each ring, and the CHELPG atomic charges were calculated. Calculated heats of formation are: pyridine +133, phosphorin +181, arsenin +231, antimonin +329, bismin +468, pyridine oxide +143, phosphorin oxide +1, arsenin oxide +183, antimonin oxide +344, bismin oxide +570, pyridine sulfide +252, phosphorin sulfide +205, arsenin sulfide +328, antimonin sulfide +435, and bismin sulfide + 642 kJ/mol. The question of aromaticity for these heterocycles was discussed. On the basis of hydrogenation energies, NICS values, and lack of bond alternation, the entire series from pyridine to bismin appears to be aromatic and to a roughly equal degree. The situation for the oxides and sulfides of pyridine, phosphorin, and arsenin is much the same, but bismin oxide and bismin sulfide are nonplanar and according to NICS nonaromatic. Antimonin oxide is aromatic by some of the criteria and nonaromatic by others.

ENAMINONES AS BULDING BLOCKS IN ORGANIC SYNTHESIS: SYNTHESIS OF NEW POLYFUNCTIONAL PYRIDINES, CONDENSED PYRIDINES AND ΡΕΝΤΑ SUBSTITUTED BENZENE

Article ENAMINONES AS BULDING BLOCKS IN ORGANIC SYNTHESIS: SYNTHESIS OF NEW POLYFUNCTIONAL PYRIDINES, CONDENSED PYRIDINES AND ΡΕΝΤΑ SUBSTITUTED BENZENE was published on April 1, 2001 in the journal Heterocyclic Communications (volume 7, issue 2).

ChemInform Abstract: The Rotational Barriers of Groups Containing Silicon in Substituted Benzenes. A Theoretical Approach to the Silicon Substituent Effect.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Rotational Barriers of Groups Containing Silicon in Substituted Benzenes. A Theoretical Approach to the Silicon Substituent Effect

The potential energy profile for a number of derivatives of benzene substituted with the SiH3, SiH2CH3, and CH2SiX3 (X = H, F, Cl, CH3) groups was calculated at ab initio (HF/6-31G*//HF/6-31G*) level, and the energy barriers were estimated. The rotational barrier is low for the molecules with silicon directly bonded to the phenyl ring, but higher values are found for the CH2SiX3 groups, which depend on X as well. The hyperconjugative effect of the substituents was estimated from the natural bond orbital (NBO) theory of donor acceptor properties: the SiH2CH3 group was found to be electron-acceptor in character, and the CH2SiX3 were found to be electron-donor groups. The rotational barrier of these molecules is mainly determined by hyperconjugation, steric effects being smaller than in the analogous carbon derivatives. The SiH and SiC bonds display an electron-acceptor character of similar magnitude when silicon is attached to the phenyl ring, but the SiC bond has a prevailing donor character when carbon i...

Ground- and Excited-State Electron Donor−Acceptor (EDA) Complexes from (Dibenzoylmethanato)boron Difluoride and Substituted Benzenes: Their Relation to the Reaction Mechanism

The ground-state EDA complex of (dibenzoylmethanato)boron difluoride (DBMBF2) with substituted benzenes (SB) was studied by absorption spectroscopy to determine the equilibrium constant and enthalpy of the molecular association process in acetonitrile and cyclohexane. Excitation of the EDA complexes showed the corresponding exciplex fluorescence due to excitation of DBMBF2 in the presence of SB. Integration of these data with the previously published kinetics and thermodynamics of the exciplex formation and decay showed that both types of excitations converged on the exciplex energy well and that the former excitation goes through the Franck−Condon state, *(A-D+)v, which is different in molecular distance and electron and energy distributions. In acetonitrile, the discrepancy of fluorescence intensities from two excitations is taken as proof for electron transfer at the encounter pair on the energy surface to generate radical ions. This also implies that excitation of EDA complexes in acetonitrile forms the corresponding exciplexes directly (without the intermediacy of the encounter pair), which undergo solvolysis to give free ions. A mechanism is proposed to represent the observed photochemistry and photophysics.

Intermolecular Dynamics of Substituted Benzene and Cyclohexane Liquids, Studied by Femtosecond Nonlinear-Optical Polarization Spectroscopy

Femtosecond time-resolved optical-heterodyne detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) is shown to be a powerful and comprehensive tool for studying the intermolecular dynamics occurring in liquids. The observed dynamics include both the underdamped, or coherent inertial motions, and the longer time scale diffusive relaxation. The inertial dynamics include phonon-like intermolecular vibrations, intermolecular collisions, and librational caging motions. Data are presented and analyzed for a series of five liquids: cyclohexane, methylcyclohexane, toluene, benzyl alcohol, and benzonitrile, listed in order of increasing polarity. We explore the effects of aromaticity (e.g., methylcyclohexane vs. toluene), symmetry reduction (cyclohexane vs methylcyclohexane), and substitution effects (e.g., substituted benzene series) on the ultrafast intermolecular dynamics, for a group of molecular liquids of similar size and volume. We analyze the intermolecular dynamics in both the time and frequency do...

Mechanistic Studies on the Dual Reaction Pathways of Singlet Excited Dibenzoyl(methanato)boron Difluoride (DBMBF2): Reactions of the Excimer and Exciplexes

The mechanism of the interaction of singlet excited dibenzoyl(methanato)boron difluoride (*DBMBF2 = *A) with olefins and substituted benzenes (SB) was investigated by the determination of effective quenching distances (Reff) from fluorescence monitors in acetonitrile as analyzed by the Smoluchowski−Collins−Kimball equation and by solvent effects on the dichotomy of the formation of cycloadducts and [4 + 2] dimers from 1,3-cyclohexadiene (CHD) and 1,3-cyclooctadiene (1,3-COD). The correlation of Reff with directly demonstrates that the reactants have to get closer to affect electron transfer from these substrates as the driving force become more positive and coalesce on exciplexes. Both photophysical and photochemical probes converge on the partition of encounter pairs to the SSRIP (the ket pathway which leads to radical ion reactions and nonfluorescent) and exciplexes (the kex pathway which leads to cycloadducts and fluorescent species); the former pathway was promoted by low redox energies of donor−accep...

ChemInform Abstract: Stabilities of Complexes of Br‐ with Substituted Benzenes (SB) Based on Determinations of the Gas‐Phase Equilibria Br‐ + SB = (BrSB)‐

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stabilities of complexes of bromide with substituted benzenes (SB) based on determinations of the gas-phase equilibria Br- + SB = (BrSB)-

Equilibria involving some forty substituted benzenes (SB) and the bromide ions (SR+Br − =SBBr − ) in the gas phase were determined with a pulsed electron, high-pressure mass spectrometer (PHPMS). The resulting −ΔG 1 ° provide information on the stabilities of the SBBr − complexes. A Taft substituent analysis of the δΔG 1 ° indicates that Br − and Cl − form aromatic C-H hydrogen-bonded complexes with all singly substituted benzenes. The field effects of the substituents provide the dominant contribution to the bonding in these complexes. Similar conclusions are reached also for the singly substituted nitrobenzenes and Br − . A clearcut analysis of the bonding to Br − when triply substituted benzenes with strongly electron withdrawing substituents like CF 3 , CN, and NO 2 are present could not be obtainted

ChemInform Abstract: Gas Phase Reactions. Part 67. On the Synthesis of Benzodithiete Derivatives by Means of Thermolysis of 1,2‐Dithio Substituted Benzenes.

AbstractThe short‐path thermolysis of the 1,2‐bis(mercapto)benzenes (Ia) and (Ib) at temperatures >700K yields the thermally unstable benzodithietes (IIa) and (IIb) which are identified by real‐time PE spectroscopic analysis.

ChemInform Abstract: Empirical Correlations in Ultraviolet Spectra of Substituted Benzenes. Part 2. Compounds with Electron‐Releasing “Parent Groups”.

ChemInform Abstract: Empirical Correlations in Ultraviolet Spectra of Substituted Benzenes. Part 2. Compounds with Electron‐Releasing “Parent Groups”.