Benzene derivatives polysubstituted

More important and more widely applicable criteria of protonation sites are available in the effects of more distant substituents, in particular meta and para in benzene derivatives, which are as a rule purely electronic in origin. Exceptionally, they may be complicated by steric effects (e.g., in polysubstituted derivatives). The most widely useful approach is that of Hammett (1940), who suggested that the effects of substituents on the ionization constants of benzoic acid may be taken as a measure of their effectiveness in other systems involving other reaction centres and in reactions other than acid-base equilibria. He thus defined substituent constants, a, by the equation... 

Finally, benzenepolycarboxylates were obtained by ruthenium-catalyzed cross-benzannulation of acetylenedicarboxylates with allylic compounds [52] (Eq. 39). A ruthenacyclopentene is postulated to occur via oxidative coupling of one molecule of alkyne with allylic alcohol. Subsequent insertion of another molecule of alkyne gives the corresponding polysubstituted benzene derivatives. 

Fig. 3a-b. Distribution of Ring Energy Content for benzenoid hydrocarbons and polysubstituted benzene derivatives. The interquartile ranges for the distribution are 25.9 kcal/mol and 16.1 kcal/mol,... 

Recent Advances In Fhe Transition Metal Catalyzed Regioselective Approaches To Polysubstituted Benzene Derivatives, Saito. S.-. Yamamoto. Y. Chem. Rev., 2000, 100, 294. 

Table 16. Mean Values of HOMA, EN, and GEO Terms for the Ring of Polysubstituted Benzene Derivatives Compared with Topologically Equivalent Rings in Benzenoid Hydrocarbons...

Cohen and Benson s) group additivity values polysubstituted benzene derivatives density functional theory strain-induced bond localization... 

Very few Ni-allene complexes have been isolated and characterized, but many such species have been postulated as key intermediates in organic transformations catalyzed by Ni precursors. Notable examples of such applications include the cyclization of two arynes and one allene to give 10-methylene-9,l-dihydrophenanthrenes, " the one-pot coupling of allenes with aldehydes and silanes to give allyl silyl ethers, selective [3+2]-cyclization of allenes and Fischer carbenes, regio- and stereoselective, three-component assembly of allenes with aryl iodides and alkenyl-zirconium reagents, and regio- and chemoselective [2+2+2]-cycloaddition of electron-deficient diynes with allenes to polysubstituted benzene derivatives. ... 

The present method was applicable to the synthesis of polysubstituted benzene compounds. For example, treatment of 20 with 2 in the presence of 10 mol % Cu(OTf)2 and 1 equiv of H2O in a mixture of 1,2-dichloroethane and CFI3CN (3 1) gave the corresponding benzene derivative 21 in 71% yield as a sole product (Scheme 15.7). 

Saito, S. and Yamamoto, Y. (2000) Recent advances in the transition-metal-catalyzed regioselective approaches to polysubstituted benzene derivatives. Chemical Reviews, 100(8), 2901-2916. 

Enynones (42) undergo carbocyclization on reaction with iodine to produce polysubstituted benzene derivatives (43). When carried out in methanol or ethanol. 

The polysubstituted benzenes 291 and 292 were also obtained by protonation of the cyclohexadiene derivatives 287 -289 (equation 101)155. The migration of the propynyl... 

Discotic liquid crystals The molecules possess a disc shape in many cases they are polysubstituted benzene or triphenyl derivatives with lateral extended aliphatic chains. These molecules arrange, e.g., in large columns a discotic nematic phase is known too. 

The strain introduced in the addition compounds causes them to readily eliminate and revert back to the parent fullerene. This makes mass spectroscopic identification of derivatives particularly difficult. A further difficulty encountered in the chemistry of fullerenes lies in the multitude of addition products that can, in principle, be obtained. For example, for C60 the number of products discounting isomers that can be produced on addition of a reagent X2 will equal the number of double bonds, i.e. 30. If isomers are included then many hundreds are possible. Development of C60 chemistry is therefore very much more difficult than that of benzene. It is also complicated by the low solubility of C60 in organic solvents, and by the fact that derivatives are themselves mostly more soluble, which facilitates polysubstitution hydroxy and amino derivatives of C60 are water-soluble. The additions are described under the two main categories outlined above. 

A few polysubstituted benzenes have been evaluated for their possible use in protozoal chemotherapy. RC-12 (57) is a pyrocatechol derivative, which was initially found to possess promising antimalarial activity. However, in clinical trials against P. vivax it failed to protect volunteers exposed to infected mosquitoes [16]. Another compound ethyl 4-acetamido-2-ethoxybenzoate (ethopabate, 58) has been found to exhibit anticoccidial activity [45,57]. Also some nitrobenzamides have been shown to have anticoccidial properties. The important drugs of this class are zoalene (59) [58], nitromide (60) [59] and alkomide (61) [45,60]. The detailed SAR on nitrobenzamides has been studied [59,61]. 

Honig, H., An Improved 13C-NMR-Shift Prediction Program for Polysubstituted Benzenes and Sterically Defined Cyclohexane Derivatives, Magn. Reson. Chem., 34, 395,... 

In the place of Cl and Br in the above examples any univalent atom or radical may be substituted, thus giving rise to a gx t number of deriva-tivea Certain of such substituted radicals determine the function of the original unisubstituted derivative of benzene and of all of its polysubstituted derivatives Thus the group (OH) is characteristic of the phenols (CH,) or + of the superior homologues of benzene (CH,OH) of the... 

In Table 10-3 we have collected experimental S values for adsorption on alumina of 48 polysubstituted benzenes and substituted naphthalenes. These data provide a good collective example of the effects of sample localization on sample adsorption energy. Values of QJ for all the groups i represented in the samples of Table 10-3 can be derived through Eq. (10-1) from experimental S values for the unsubstituted hydrocarbons, benzene and naphthalene, and appropriate monosubstituted benzenes e.g., anisole, nitrobenzene, aniline.t Table 10-2 summarizes these values. This in turn permits the calculation of 2 Ql for each of the compounds of Table 10-3. The latter quantity will be equal to S for the compound in question, if Eq. (10-1) applies and 0 values for a given group i are constant in all compounds of which i is a part. However, the localization of a polyfunctional sample moleculej should be reflected in a value of S which is less than because of the corresponding delocalization of some... 

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