Aromatic Hydrocarbons and Their Derivatives

Aromatic hydrocarbons, sometimes referred to as arenes, can be considered to be derived from benzene, C6H6. Benzene is a transparent, volatile liquid (bp = 80°C) that was discovered by Michael Faraday in 1825. Its formula, C6H6, suggests a high degree of unsaturadon, yet its properties are quite different from those of alkenes or alkynes. 

As pointed out in Chapter 7, the atomic orbital (valence bond) model regards benzene as a resonance hybrid of the two structures 

In these line-angle formulas it is understood that there is a carbon atom at each vertex of the hexagon hydrogen atoms are not shown. This model is consistent with many of the properties of benzene. The molecule is a planar hexagon with bond angles of 120°. The hybridization of each carbon is sp2. However, this structure is misleading in one respect Chemically, benzene does not behave as if double bonds were present 

A more satisfactory model of the electron distribution in benzene, based on molecular orbital theory (Appendix 5), assumes that— 

At one time, benzene was widely used as a solvent, both commercially and in research and teaching laboratories. Its use for that purpose has largely been abandoned because of its toxicity. Chronic exposure to benzene vapor leads to various blood disorders and, in extreme cases, 

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An excess of crotonaldehyde or aUphatic, ahcyhc, and aromatic hydrocarbons and their derivatives is used as a solvent to produce compounds of molecular weights of 1000—5000 (25—28). After removal of unreacted components and solvent, the adduct referred to as polyester is decomposed in acidic media or by pyrolysis (29—36). Proper operation of acidic decomposition can give high yields of pure /n j ,/n7 j -2,4-hexadienoic acid, whereas the pyrolysis gives a mixture of isomers that must be converted to the pure trans,trans form. The thermal decomposition is carried out in the presence of alkaU or amine catalysts. A simultaneous codistillation of the sorbic acid as it forms and the component used as the solvent can simplify the process scheme. The catalyst remains in the reaction batch. Suitable solvents and entraining agents include most inert Hquids that bod at 200—300°C, eg, aUphatic hydrocarbons. When the polyester is spHt thermally at 170—180°C and the sorbic acid is distilled direcdy with the solvent, production and purification can be combined in a single step. The solvent can be reused after removal of the sorbic acid (34). The isomeric mixture can be converted to the thermodynamically more stable trans,trans form in the presence of iodine, alkaU, or sulfuric or hydrochloric acid (37,38). 

Oja, V., Suuberg, E.M. (1998) Vapor pressures and enthalpies of sublimation of polycyclic aromatic hydrocarbons and their derivatives. J. Chem. Eng. Data 43, 486 -92. 

Classical organic chemistry provides a wide variety of potential analytes for electron ionization, the only limitation being that the analyte should be accessible to evaporation or sublimation without significant thermal decomposition. These requirements are usually met by saturated and unsaturated aliphatic and aromatic hydrocarbons and their derivatives such as halides, ethers, acids, esters, amines, amides etc. Heterocycles generally yield useful El spectra, and flavones, steroids, terpenes and comparable compounds can successfully be analyzed by El, too. Therefore, El represents the standard method for such kind of samples. 

Airborne Polycyclic Aromatic Hydrocarbons and Their Derivatives... 

Chuang, J. C., G. A. Mack, M. R. Kuhlman, and N. K. Wilson, Polycyclic Aromatic Hydrocarbons and Their Derivatives in Indoor and Outdoor Air in an Eight-Home Study, Atmos. Environ., 25B, 369-380 (1991). 

Prycek, J., M. Ciganek, and Z. Simek. 2004. Development of an analytical method for polycyclic aromatic hydrocarbons and their derivatives. J. Chromatogr. A 1030 103-107. 

As noted in [2], fullerenes dissolve better in aromatic hydrocarbons and their derivatives, among which naphthalene derivatives occupy the first place. High... 

Ever since Cram started his systematic efforts to study bridged aromatic hydrocarbons and their derivatives half a century ago [62, 63], this field has had a strong influence on the development of aromatic chemistry [64-67]. In fact, after a period during which numerous cyclophane hydrocarbons were prepared and their chemical and structural properties were studied, their derivatives are now enjoying growing attention as chiral ligands in reagents... 

Like silica, alumina is also a typical adsorbent with polar characteristics. Although the order of separation for the majority of organic compounds is the same or very similar in alumina as in the case of silica, alumina may give a better separation than silica for several compound groups such as molecules containing carbon-carbon double bonds, aromatic hydrocarbons and their derivatives, including the possible separation of some isomers. 

Polycyclic aromatic hydrocarbons and their derivatives arc part of a great group of toxic compounds and some known carcinogens. The possible health risk to humans through inhalation or ingestion of these PAHs makes necessary the determination of these compounds, to reduce its concentration in the emissions. 

Typical for aromatic hydrocarbons and their derivatives are the Lb, Lj, Bb, and Bj, bands. Chirally twisted aromatic compounds, for example, hexa-helicene (2), are inherently dissymmetric n chromophores. The rotatory strength of the various transitions can be calculated by means of the common r-electron methods. 

The fluorescence detector is a specific and concentration-sensitive detector. It is based on the emission of photons by electronically excited molecules. Fluorescence is especially observed for analytes with large conjugated ring systems, e.g., polynuclear aromatic hydrocarbons and their derivatives. In order to extend its applicability range, pre-column or post-column derivatization strategies have been developed [9]. 

Coal fragments, when heated in the absence of oxygen, yield coal tar, which contains many aromatic hydrocarbons and their derivatives. Consequently, coal is used as a raw material for other chemicals. 

Chuang JC, Mack GA, Kuhlman MR, et al. 1991. Polycyclic aromatic hydrocarbons and their derivatives in indoor and outdoor air in an eight-home study. Atmos Environ Part B Urban Atmos 25(3) 369-380. 

Three patents issued in 1924 and 1925 are conspicuous as placing special emphasis upon the preparation of particular catalysts as suitable for reactions involving the partial oxidation of side chains present in aromatic nuclei. The first00 of these relates to the oxidation of aromatic hydrocarbons and their derivatives, viz., toluene, xylene, cymene, cumene, mesitylene, cresols, etc., together with their derivatives including nitro-... 

Kohlenwasserstoffe und ihrer Abkommlinge. I. Dibenzanthracene und ihrer Chinone [Knowledge of polynuclear aromatic hydrocarbons and their derivatives. 774. 

Chlorinated organic compounds (COCs) refer to the substitution of one or more hydrogen in aliphatic and aromatic hydrocarbons and their derivatives by chlorine. COCs are widely used in the fields of chemistry, medicine, electronics, pesticides, etc. Many COCs are endocrine disturbance substances, show carcinogenic effects, and have been listed as priority pollutants by the US Environmental Protection Agency (USEPA). When released into the environment, COCs are transported in both air and water. However, COCs are chemically stable and difficult to destroy, and they are eventually deposited in soils and sediments due to their hydrophobic-ity. Soils and sediments contaminated with COCs are long-term sources of pollutants and pose great threats to human health and ecosystems. Therefore, remediation of these contaminated soils and sediments is of great importance. 

For the generation of dications from polycyclic aromatic hydrocarbons and their derivatives see Sect, IV.6. The interconversions between dications [ArCH Rf and benzyl- pe cations [ArCHR] are discussed in . The proton was only lost from the dication corresponding to 9-ethylanthracene (R=CH3>. 

In spite of intensive studies of phosphine-containing catalysts for hydroformylation and their application in industry, publications concerning the stability of these catalysts under conditions of hydroformylation reactions have appeared only recently.It was found that the phosphorus-carbon bond is relatively rapidly broken. The decomposition of triarylphosphines leads to the formation of alkyldiarylphosphines as well as aromatic hydrocarbons and their derivatives such as aldehydes and alcohols. Several... 

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