Benzene aromaticity

Initial portion of the TBP curve of a Saharan crude oil (Note the discontinuities due to the presence of aromatics benzene B, toluene T, xylenes X). 

Aromatics - Benzene, Methylbenzene (Toluene) Dimethylbenzene (Xylenes) Naphthenes - Cyclopentane, Cyclohexane... 

If you request a semi-empirical quantum mechanical calculation now, HyperChem carries on as well as possible (as described below) in choosing how the atoms for quantum mechanical calculation is capped. If, however, an aromatic benzene ring (with delo-... 

Hydrocarbons, compounds of carbon and hydrogen, are stmcturally classified as aromatic and aliphatic the latter includes alkanes (paraffins), alkenes (olefins), alkynes (acetylenes), and cycloparaffins. An example of a low molecular weight paraffin is methane [74-82-8], of an olefin, ethylene [74-85-1], of a cycloparaffin, cyclopentane [287-92-3], and of an aromatic, benzene [71-43-2]. Cmde petroleum oils [8002-05-9], which span a range of molecular weights of these compounds, excluding the very reactive olefins, have been classified according to their content as paraffinic, cycloparaffinic (naphthenic), or aromatic. The hydrocarbon class of terpenes is not discussed here. Terpenes, such as turpentine [8006-64-2] are found widely distributed in plants, and consist of repeating isoprene [78-79-5] units (see Isoprene Terpenoids). 

Common examples of compounds that are amenable to carbon adsorption are aromatics (benzene, toluene) and chlorinated organics (trichloroethylene, trichloroethane [71-55-6, 75 -(9(9-j5y, tetrachloroethylene, polychlorinated biphenyls (PCBs), DDT /T(9-77-77, pentachlorophenol [87-86-5J. Compounds that are not adsorbed effectively by carbon include ethanol [64-17-5], diethylene glycol [111-46-6], and numerous amines (butylamine [109-73-9, 13952-84-6, 75-64-9], triethanolamine [102-71-6], cyclohexylamine [108-91-8], hexamethylenediamine [108-91-8] (1). Wastewater concentrations that are suitable for carbon adsorption are generally less than 5000 mg/L. 

Observable Characteristics - Physical State (as normally shipped) Liquid Color Colorless Odor Pungent aromatic, benzene-like distinct, pleasant. 

For aromatics production, similar considerations apply. Maximum yields of xylenes and other heavy aromatics can be obtained in cyclic units, but, again, at somewhat higher investments. The process selection, thus, again requires the balancing of process credits versus debits for the specific application. For light aromatics (benzene-toluene) production, however, the situation tends to favor a... 

Three tautomeric structures (1,2-dihydro 27, 1,4-dihydro 28, and 3,4-dihydro 29) are possible for N-unsubstituted dihydroquinolines, which retain the aromatic benzene ring, and two structures 27 and 28 for N-substituted derivatives. No information on the tautomerism of such dihydroquinolines and stability of the possible tautomers was available when the earlier review (76AHCS1) was published. 

The sulfolane process is a versatile extractant for producing high purity BTX aromatics (benzene, toluene, and xylenes). It also extracts aromatics from kerosines to produce low-aromatic jet fuels. 

It is evident that the yield of aromatics (benzene) is favored at higher temperatures and lower pressures. The effect of decreasing H2 partial pressure is even more pronounced in shifting the equilibrium to the right. 

Starting January 1998, the EPA s Complex Model went into effect. The Complex Model provides a set of equations that predict VOC, NO, and toxic emissions, using eight gasoline properties. These properties are RVP, oxygen, aromatics, benzene, olefins, sulfur, E200. 

The most common hydrophobes used as the basis for surfactants are those containing eight to eighteen carbon atoms, such as those listed as carboxylates in Table 9.1. Some hydrophobes are aromatic (benzene or naphthalene) moieties, often containing lower alkyl substituents dodecylbenzene (9.1) is a common example. Alkyl-substituted toluenes, xylenes and phenols, and mono- and di-alkylated naphthalenes (9.2 and 9.3), are also used. 

Also as noted above any substituents present have little effect upon such oxidations. In 2,2 -methylenedifuran (118) the rings are attacked simultaneously giving a tetramethoxy derivative.297 Even the bulk of the fert-butyl group has little effect.298 The only marked substituent effect is that exerted by an aromatic (benzene, thiophene, furan) residue which, if directly attached at the 2-position, promotes elimination instead of the addition of another methoxy group. The net process then becomes one of arylation, as when 2-(2-thienyl)furan (119) is oxidized to 120.298 There are reports that acetyl and carboxy groups can be ejected during oxidation, but that ester groups are usually retained.287... 

Wahner, A., Zetzsch, C. (1983) Rate constants for the addition of hydroxyl radicals to aromatics (benzene, p-chloroaniline, and o-, m- and p-dichlorobenzene) and the unimolecular decay of the adduct. Kinetics into a quasi-equilibrium. J. Phys. Chem. 87, 4945 -951. 

Two rings linked by sharing the same bond instead of the same atom lead to annulated bicyclic or tricyclic compounds, the propellanes. In the case of poly-unsaturated molecules, an interesting case is represented by the bicyclo[2.2.0] type. The parent compound Dewar benzene (bicyclo[2.2.0]hexa-2,5-diene) (DEW) is the smallest bicyclic diene which is an often discussed valence isomer of aromatic benzene Unsubstituted DEW is a very... 

Taskinen and Nummelin (op. cit.) reported many other isomer equilibria in their paper. Most of these used cyclohexane as the solvent and I2 as the catalyst and so are not confounded by solvent effects. However, these authors noted that hydrogen atom transfer induced disproportionation (to form the aromatic benzene) dominates this reaction for the case of 49/50 isomerization and so they needed alternative reaction conditions. 

Table 3.2. Lewis (L) and non-Lewis (NL) energy contributions and NBO occupancies for sigma and pi bonds of the simplest alkane (CH4), alkene (C2H4), and alkyne (C2H2) species, with aromatic benzene (C fD includedfor...

Anions of CH-acidic compounds (dimethyl malonate and nitromethane) can he linked to aromatics (benzene, toluene, naphthalene, and 1,4-dimethoxybenzene) when they are coelectrolyzed in methanol-sodium methoxide [167]. 

Scientists classify hydrocarbons as either aliphatic or aromatic. An aliphatic hydrocarbon contains carbon atoms that are bonded in one or more chains and rings. The carbon atoms have single, double, or triple bonds. Aliphatic hydrocarbons include straight chain and cyclic alkanes, alkenes, and alkynes. An aromatic hydrocarbon is a hydrocarbon based on the aromatic benzene group. You will encouter this group later in the section. Benzene is the simplest aromatic compound. Its bonding arrangement results in special molecular stability. 

Aromatics (benzene, toluene, m-xylene, mesitylene) from olefin (octene) NaX, NaY [144]... 

Zeolite S1O2/ Metal Feed SV Temp Pressure Conversion Aromatics Benzene Notes Reference... 

Fuel oils are petroleum products that are used in many types of engines, lamps, heaters, furnaces, stoves, and as solvents. Fuel oils come from crude petroleum and are refined to meet specifications for each use. Fuel oils are mixtures of aliphatic (open chain and cyclic compounds that are similar to open chain compounds) and aromatic (benzene and compounds similar to benzene) petroleum hydrocarbons. In addition, they may contain small amounts of nitrogen, sulfur, and other elements as additives. The exact chemical composition (i.e., precise percentage of each constituent) of each of the fuel oils discussed in this profile may vary... 

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