Aromaticity polycyclic aromatic hydrocarbons

A radical reacting with a molecule must produce a particle with an unpaired electron. For the reacting molecule to be called an inhibitor, these secondary radicals should have negligible tendency to propagation. They can have various fates. They either dimerize or react with a further radical that is able to propagate. The initiation rate can be determined by means of an ideal inhibitor. The most important inhibitors are some quinones, nitro and nitroso aromatics, polycyclic aromatic hydrocarbons, some metal chlorides, and stable radicals (e.g. I,l-diphenyl-2-picrylhydrazyl-DPPH, etc.). 

Reactivity numbers of the most reactive positions have been used to correlate the reactivities in nitration (see below) and other substitutions of a series of polycyclic aromatic hydrocarbons, and they give somewhat better correlations than any of the other commonly used indices of reactivity. The relationship shown below, which was discussed earlier ( 7.1.1),... 

Members of a class of arenes called polycyclic aromatic hydrocarbons possess subslanlial resonance energies because each is a colleclion of benzene rings fused logelher... 

A large number of polycyclic aromatic hydrocarbons are known Many have been synthesized m the laboratory and several of the others are products of com bustion Benzo[a]pyrene for example is present m tobacco smoke contaminates food cooked on barbecue grills and collects m the soot of chimneys Benzo[a]pyrene is a carcinogen (a cancer causing substance) It is converted m the liver to an epoxy diol that can induce mutations leading to the uncontrolled growth of certain cells... 

Polycyclic aromatic hydrocarbons, of which anthracene is an example contain two or more benzene rings fused together... 

Polycyclic aromatic hydrocarbons undergo electrophilic aromatic substitution when treated with the same reagents that react with benzene In general polycyclic aromatic hydrocarbons are more reactive than benzene Most lack the symmetry of benzene how ever and mixtures of products may be formed even on monosubstitution Among poly cyclic aromatic hydrocarbons we will discuss only naphthalene and that only briefly Two sites are available for substitution m naphthalene C 1 and C 2 C 1 being normally the preferred site of electrophilic attack... 

Section 12 17 Polycyclic aromatic hydrocarbons undergo the same kind of electrophilic aromatic substitution reactions as benzene... 

Polyamine (Section 22 4) A compound that contains many ammo groups The term is usually applied to a group of nat urally occurring substances including spermine spermi dine and putrescme that are believed to be involved in cell differentiation and proliferation Polycyclic aromatic hydrocarbon (Section 118) An aromatic hydrocarbon charactenzed by the presence of two or more fused benzene rings... 

Wingen, L. M. Low, J. C. Pinlayson-Pitts, B. J. Chromatography, Absorption, and Pluorescence A New Instrumental Analysis Experiment on the Measurement of Polycyclic Aromatic Hydrocarbons in Cigarette Smoke, ... 

As with the parent aromatic hydrocarbons, diarylamiaes based oa polycyclic aromatic amines also tead to be more harmful. Thus, /V-phenyl-2-naphthylamine [135-88-6] (PBNA) metaboli2es ia the body to produce small amouats of 2-aaphthylamiae, a known carciaogea (37). ACGIH has desigaated PBNA to be an "iadustrial substance suspect of carciaogenic potential for man."... 

Unbumed Hydrocarbons Various unburned hydrocarbon species may be emitted from hydrocarbon flames. In general, there are two classes of unburned hydrocarbons (1) small molecules that are the intermediate products of combustion (for example, formaldehyde) and (2) larger molecules that are formed by pyro-synthesis in hot, fuel-rich zones within flames, e.g., benzene, toluene, xylene, and various polycyclic aromatic hydrocarbons (PAHs). Many of these species are listed as Hazardous Air Pollutants (HAPs) in Title III of the Clean Air Act Amendment of 1990 and are therefore of particular concern. In a well-adjusted combustion system, emission or HAPs is extremely low (typically, parts per trillion to parts per billion). However, emission of certain HAPs may be of concern in poorly designed or maladjusted systems. 

POLYCYCLIC AROMATIC HYDROCARBONS LUMINESCENCE DETERMINATION USING MICELLAR SOLUTIONS... 

The performance of microwave-assisted decomposition of most difficult samples of organic and inorganic natures in combination with the microwave-assisted solution preconcentration is illustrated by sample preparation of carbon-containing matrices followed by atomic spectroscopy determination of noble metals. Microwave-assisted extraction of most dangerous contaminants, in particular, pesticides and polycyclic aromatic hydrocarbons, from soils have been developed and successfully used in combination with polarization fluoroimmunoassay (FPIA) and fluorescence detection. 

Aromatic solvents or polycyclic aromatic hydrocarbons (PAFI) in water, e.g. can be detected by QCM coated with bulk-imprinted polymer layers. Flere, the interaction sites are not confined to the surface of the sensitive material but are distributed within the entire bulk leading to very appreciable sensor responses. Additionally, these materials show high selectivity aromatic solvents e.g. can be distinguished both by the number of methyl groups on the ring (toluene vs. xylene, etc.) and by their respective position. Selectivity factors in this case reach values of up to 100. 

ACID-BASED SURFACTANT CLOUD POINT EXTRACTION AND PRECONCENTRATION OF POLYCYCLIC AROMATIC HYDROCARBONS PRIOR TO FLUORESCENCE DETERMINATION... 

A number of airborne chemical contaminants are EDs, particularly products of combustion such as dioxins and polycyclic aromatic hydrocarbons. ... 

An appreciation of the extent to which invertebrate species may be exposed to such chemicals comes from considering the effects of complex mixtures. In the North Atlantic ecosystem alone, hundreds of pollutant chemicals have been identified. These include metals, synthetic and chlorinated organics and polycyclic aromatic hydrocarbons. Over 300 aromatic hydrocarbons have been detected in some regions of the Chesapeake Bay, and high concentrations of PCBs have been... 

Table 9.3. Rate of Diel-Alder Additions of Linear Polycyclic Aromatic Hydrocarbons"...

Comparison of localization energies has frequently been applied to prediction of the relative positional reactivity in polycyclic aromatic hydrocarbons. Simple HMO calculations have only marginal success. CNDO/2 and SCF calculations give results which show good correlation with experimental data on the rate of proton exchange. ... 

The polycyclic aromatic hydrocarbons such as naphthalene, anthracene, and phenan-threne undergo electrophilic aromatic substitution and are generally more reactive than benzene. One reason is that the activation energy for formation of the c-complex is lower than for benzene because more of the initial resonance stabilization is retained in intermediates that have a fused benzene ring. 

Halogenated chemicals Polycyclic aromatic hydrocarbons Aliphatics Substituted benzenes Halogenated aliphatics Dioxins and furans... 

Carcinogens Cancer-producing agents Skin Respiratory Bladder/urinary tract Liver Nasal Bone marrow Coal tar pitch dust crude anthracene dust mineral oil mist arsenic. Asbestos polycyclic aromatic hydrocarbons nickel ore arsenic bis-(chloromethyl) ether mustard gas. p-naphthylamine benzidine 4-am i nodi pheny lam ine. Vinyl chloride monomer. Mustard gas nickel ore. Benzene. 

Particulate polycyclic aromatic hydrocarbons (PPAH), see Coal tar pitch volatiles... 

BS ISO 12884 Polycyclic aromatic hydrocarbons Collection of filters with gas chromatography/mass spectrometry... 

Coal tar pitch volatiles, see Particulate polycyclic aromatic hydrocarbons (PPAH), as benzene solubles Cobalt metal, dust and fume (as Co)... 

PAH Polycyclic Aromatic Hydrocarbons, (rarely used as abbreviation for polyaluminum hydroxide)... 

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