Aromatic compound characteristics

Determination of purity. The ultraviolet and visible absorption is often a fairly intensive property thus e values of high intensity bands may be of the order of 10 -10 . In infrared spectra e values rarely exceed 10 . It is therefore often easy to pick out a characteristic band of a substance present in small concentration in admixture with other materials. Thus small amounts of aromatic compounds can be detected in hexane or in cyclohexane. 

Characteristics of the system as nitrating reagents Wibaut, who introduced the competitive method for determining reactivities (his experiments with toluene, benzene and chlorobenzene were performed under heterogeneous conditions and were not successful), pointed out that solutions of nitric acid in acetic anhydride are useful in making comparisons of reactivities because aromatic compounds are soluble in them. ... 

Werner complexes can be used to form clathrates with the Cg aromatic isomers (35—42). The aromatic compounds are released upon heating. Since the uptake and release characteristics of the four Cg aromatic isomers are each different, this method has been suggested as a means of separating the isomers. 

In general, the dissection of substituertt effects need not be limited to resonance and polar components, vdiich are of special prominence in reactions of aromatic compounds.. ny type of substituent interaction with a reaction center could be characterized by a substituent constant characteristic of the particular type of interaction and a reaction parameter indicating the sensitivity of the reaction series to that particular type of interactioa For example, it has been suggested that electronegativity and polarizability can be treated as substituent effects separate from polar and resonance effects. This gives rise to the equation... 

Another characteristic of aromatic compounds is a relatively large HOMO-LUMO gap, which can be expressed in terms of hardness, t] (see p. 21 for the definition of hardness) ... 

The A-ring of the 17-ol (25) derived from equilenin 3-methyl ether is reduced rapidly under Birch reduction conditions, since the 1,4-positions are unsubstituted. The B-ring is reduced at a much slower rate, as is characteristic of aromatic compounds in which 1,4-reduction can occur only if a proton enters an alkylated position. Treatment of (25) with sodium and t-butyl alcohol in ammonia reduces only the A-ring to afford the corresponding 1,4-dihydro compound in over 85% yield.On the other hand,... 

The whole reaction pattern of the thiophene-1,1-dioxides is thus characteristic of unsaturated, and not of aromatic, compounds. 

Solution The spectrum shows an intense absorption at 1725 cm- due to a carbonyl group (perhaps an aldehyde, -CHO), a series of weak absorptions from 1800 to 2000 cm-1, characteristic of aromatic compounds, and a C—H absorption near 3030 cm-1, also characteristic of aromatic compounds. In fact, the compound is phenylacetaldehyde. 

The most common reaction of aromatic compounds is electrophilic aromatic substitution. That is, an electrophile reacts with an aromatic ring and substitutes for one of the hydrogens. The reaction is characteristic of all aromatic rings, not just benzene and substituted benzenes. In fact, the ability of a compound to undergo electrophilic substitution is a good test of aromaticity- . 

All the known porphyrin isomers are typical benzoid aromatic compounds which show distinctly porphyrin-like characteristic electronic absorption spectra.13 Also the complexation properties for metal ions, NH tautomerism and the NMR spectra are quite similar to the parent porphyrin structure. 

In Figure 13.2, the intensity of the ion at m/z 170 represents a molecular ion of an aromatic compound. The characteristic losses from the molecular ion (M - 1, M - 28, and M - 29) suggest an aromatic aldehyde, phenol, or aryl ether. The molecular formula of Ci2H 0O is suggested by the molecular ion at m/z 170, which can be either a biphenyl ether or a phenylphenol. The simplest test to confirm the structure is to prepare a TMS derivative, even though m/z 11 strongly indicates the diaryl ether. 

Aromatic organic chemistry is a special branch of organic chemistry because the six-membered carbon rings that define aromatic compounds are exceptionally stable and act as central supports to which other groups can be attached. The name aromatic was given to early isolated examples of these compounds because they have characteristic odors. 

Silica sol-gel inunobihzed La(OTf)3 (Scheme 48.2B) previously used in the acylation of a series of alcohols and activated aromatic compounds using acetic anhydride as acylating agent, showed a poor activity compared with other various sihca sol-gel inunobihzed triflate derivatives (tert-butyl-dimethylsilyl-trifluoromethane-sulfonate (BDMST), or trifhc acid (HOTf)). Acylation at the aromatic ring occurred over the BDMST and HOTf catalysts, while the La(OTl)3 catalysts only led to O-acetylated products [22]. Such behavior is characteristic... 

Aromatic compounds react with mercuric salts to give arylmercury compounds.69 Mercuric acetate or mercuric trifluoroacetate are the usual reagents.70 The reaction shows substituent effects that are characteristic of electrophilic aromatic substitution.71 Mercuration is one of the few electrophilic aromatic substitutions in which proton loss from the a complex is rate determining. Mercuration of benzene shows an isotope effect kB/kD = 6,72 which indicates that the [Pg.1026]

Photoexcited aromatic compounds undergo substitution reactions with (non-excited) nucleophiles. The rules governing these reactions are characteristically different and often opposite to those prevailing in aromatic ground state chemistry 501a,b>, in contrast to the well known ortho/para activation in thermal aromatic substitutions, nitro groups activate the meta position in the photochemical substitution, as shown in (5.1) 502). 

In the past, general chapters and reviews have been published, related to the characteristics of CL as analytical technique [7-9], mainly in the liquid phase [10-14], and its use as detection mode in flowing streams and immunoassay [15-17]. Two extensive reviews reported on the specific application of CL reactions according to the nature of the analyte (inorganic species, enzymes and nucleotides, acids and amines, carbohydrates, steroids, polycyclic aromatic compounds, and drugs) and covering the literature from 1983 to 1991 [18] and from 1991 to mid-1995 [19]. 

Different organic functional groups (i.e., methyl, methylene, phenyl, and the hydrogen atoms adjacent to the carbonyl carbon in aldehydes and organic add groups) absorb at different frequencies and thus can be easily identified. Similarly, different 13C environments result in different absorption characteristics. For instance, carbon atoms in aromatic compounds absorb different frequencies than do those in carbonyl groups. 

The carcinogenicity of polycyclic aromatic compound-rich tyre extender oils has lead to the proposal of a legislative ban on their use in Europe. The suitability of naphthenic oils as non-toxic plasticisers in tyre treads is discussed and results are presented of experimental studies of the use of these plasticisers in SBR, EPDM, sulphur-cured EPDM and peroxide-cured EPDM. Despite their low aromatic content, the naphthenic plasticisers are shown to give good results in SBR, probably as a result of the contribution to solvent characteristics of the naphthenic molecular structure. The use of naphthenic oils is expected to increase worldwide as they are said to be one of the best alternatives to aromatic extracts with regard to solvent properties, compatibility, performance and availability. 

The nitro group is of high importance in organic chemistry, in particular in aromatic compounds because of its strong electron acceptor capacity. In accordance with this property, the nitro group has low-lying occupied and unoccupied orbitals, and the characteristic IPs of nitro compounds are usually found higher than 10 eV, which may lead to problems in the analysis of PE spectra. 

A striking characteristic of the 1H—NMR spectrum of the bridged aromatic compound 51 is the shift of the nuclear protons to higher field strength the aromatic hydrogen nuclei in 4,7,12,15-tetramethyl-... 

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