Aromatic systems and

Trifluoromethanesulfonic (triflic) anhydride is commercially available or can be prepared easily by the reaction of triflic acid with phosphorus pentoxide [66] This moderately hygroscopic colorless liquid is a useful reagent for the preparation of various organic derivatives of triflic acid A large variety of organic ionic triflates can be prepared from triflic anhydride A recent example is the preparation of unusual oxo-bridged dicatiomc salts of different types [SS, 89, 90, 91, 92, 93] (equations 38-44) Stabilized dication ether salts of the Huckel aromatic system and some other systems (equations 38 and 39) can be prepared in one step by the... 

In the substituted 2-pyrazoline ring (27) both nitrogen atoms have lone pairs of electrons available those on N-1 are no longer involved in an aromatic system, and in the two cases so far reported the salt... 

The central C-C double bond of dibenz[, /]oxepin displays the properties of an activated aromatic system and undergoes substitution reactions. Nitration and acid-catalyzed dcutcration gives the dibenzo[i>,/]oxepins 1 with the respective substituent in position 10.161... 

There is one other substituent which is comparable with the diazonio group in the sense that it is cationic and that it has, in one of its mesomeric structures, a triple bond between the atom attached to the aromatic system and the second atom. It is the acylium group in 7.9. However, no substituent constants are known for this group, obviously because this cation is detectable in measurable concentrations only in superacidic media (see review by Olah et al., 1976). 

Numerous chemical reactions have been carried out on ferrocene and its derivatives.317 The molecule behaves as an electron-rich aromatic system, and electrophilic substitution reactions occur readily. Reagents that are relatively strong oxidizing agents, such as the halogens, effect oxidation at iron and destroy the compound. 

The first step of a free radical aromatic substitution, the formation of the a-com-plex, is also an addition step. The o,m,p-product ratio therefore also responds to steric effects. This is shown for the free radical phenylation and dimethylamination of toluene and r.-butylbenzene in Table 8. The larger the substituent on the aromatic system and the bulkier the attacking radical, the more p-substitution product is obtained at the expense of o-substitution. In the phenylation reaction the yield of m-product also increases in contrast to the dimethylamination reaction. The substitution pattern of this latter reaction is, in addition to the steric effect, governed heavily by polar effects because a radical cation is the attacking species113. ... 

The most obvious effect on cycloaromatization, as the name implies, is the formation of an aromatic system. By delocalizing electrons in an aromatic ring, the product gains a high degree of stability, which is reflected in the small endothermicity of the Bergman cyclization and the exothermicity of the Myers-Saito cyclization. Since the Schmittel and Schreiner cyclizations are not true cycloaromatization reactions per se, they do not have the beneficial effect of the formation of an aromatic system and are therefore much are more endothermic than their counterparts. 

Most of the (5,5) (2N2)-fused heterocyclic systems are fully substituted aromatic systems and therefore they do not have any hydrogens attached to the ring. Very little is reported on C-unsubstituted compounds. Methine groups are generally part of a ring azomethine moiety and are either linked to a fusion atom C or N or to a nonfusion atom N or S (Table 1). 

Our success in super-stabilization of cation 6 led us to the preparation of a higher homologue, that is, cyclooctatetraene (COT), fully annelated with BCO units 9 (9). As compared with a large number of studies on its radical anion or dianions, the studies on the cationic species of COT have been quite limited. There have been only one study by Olah and Paquette on the substituted COT dication (70), which is a typical 6n Hiickel aromatic system, and few sporadic studies on radical cations, which involve indirect spectral observations, such as electronic spectra in Freon matrix at low temperature (77,72) and constant-flow ESR study (13). 

Several synthetic pathways for the commercial manufacture of quinacridone pigments have been published. In this context, only those routes are mentioned which were developed for industrial scale production. There are four options, the first two of which are preferred by the pigment industry. It is surprising to note that these are the methods which involve total synthesis of the central aromatic ring. On the other hand, routes which start from ready-made aromatic systems and thus might be expected to he more important actually enjoy only limited recognition. 

The Hammett equation has been further extended to include substituents of aliphatic systems too. In this case the constants that quantify the inductive effects, which are represented as o, have different values compared to those concerned with aromatic systems and are defined as Taft constants. Some values of these latter are also reported in Table 1. 

In addition to these kinetic investigations, which were in part carried out with a view to the basicity of the aromatic substances, numerous investigations have also been carried out on the subject of electrophilic substitution of aromatic systems, and all of these ultimately show, directly or indirectly, a dependence on the basicity of the aromatic substance (cf. Mason, 1958, 1959 Gould, 1962 Brown and Stock, 1962). 

Sulfite is an extremely good nucleophile for activated aromatic systems and reaction with l-substituted-2,4,6-trinitrobenzenes (1) may result in cr-adduct formation or in displacement of the 1-substiment as shown in Scheme 1. When X = OEt or SEt, adducts (2) and (3) formed by reaction at unsubstituted positions are long-lived. 

Reduction of arenediazoninm salts provides the basis for a substantial number of chemical reactions. A notable application is the Sandmeyer reaction, which utilizes the diazo moiety to facilitate functionalization of aromatic systems and remains one of the most reliable transformations in organic chemistry. The general reaction involves the addition of the cuprate salt of the desired moiety to the diazonium species—ArN2 + CuX — ArX. 

Although boranes and hydrocarbons are more notable for their differences than for any similarities, there are several important hydrocarbon systems that adopt structures that conform to the borane pattern (202). They include tnetal-hydrocarbon v complexes, various aromatic systems, and certain other neutral or charged hydrocarbons. Representative examples are listed in Table VII. 

All substituents influence the resonance in any aromatic system, and they may do this in a number of ways ... 

The UV spectrum (/Imax 246, 251, 257, 307, and 341 nm) of cyclomahanimbine (151) indicates the presence of a carbazole framework with an ether oxygen at C-2. This assignment was supported by the IR spectrum [v ax 1602, 1615 (aromatic system), and 3425 (NH) cm ]. On hydrogenation, cyclomahanimbine yielded the corresponding dihydro derivative, which did not show any shift of the absorption... 

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