Fused Five- and Six-Membered Rings

Effects of substituents on pKa values and tautomerism have been considered for benzimidazoles116 312,375 376 and 2-arylbenzimidazoles312 (53, Y = NH) as well as the corresponding oxazoles (53, Y = O) and thiazoles (53, X = S).312 Curiously, the latter two correlate with o+ for the X-substituent, and the former with a presumably this results from 

Other pA a studies include those on 6-substituted 7-azaindoles and 7-azaindolines,377 benzoxazolines and benzoxazolthiones substituted in the 5-, 6-, and 7-positions,378 purines, for which the basic centre appears to be located in the pyrimidine nucleus,379 4,4 -, 5,5 -, 6,6 -, and 7,7 -disubstituted leucothioindigos,380 and dyes (54).381 

The acid-base equilibria of 5- and 6-substituted indole carboxylic acids and coumarylic acids can be correlated with om for groups in the 5-position and op for groups in the 6-position,382 confirming the insulating effect of the heteroatom to resonance effects. 

For systems containing two heteroatoms in the five-membered component the use of mixed (/-constants must be considered. These have been used for the correlation of pAVs of benzimidazoles for which (am + op) is required for the 5- and 6-substituted compounds and (a + oa) for the 4 and 7.383 This approach has been extended to the study of nucleophilic substitution in 2-chloro-7V-methylbenzimidazoles,384 385 2- 

5-disubstituted 3,3-dimethyl-6 -nitro-8 -bromospiro [(2 H-1 -benzo-pyran 2,2 -indolines], 55 == 56.396 Information is also available on substituent effects in the decomposition of molecular ions of anilides of indole 2- and 3-carboxylic acids.397 

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M. P. Groziak and F. G. Jacobs, Tricyclic Systems Central Carbo-cyclic Ring with Fused Five- and Six-membered Rings Chapter 7.22 pp. 875-919 in Katritzky A. R., Rees Ch. W., and Scriven E. F. V, Comprehensive Heterocyclic Chemistry II A review of the Literature 1982-1995, Vol. 7 Fused Five- and Six-membered Rings without Ring Junction Heteroatoms, vol. ed. Ramsden Ch. A., Elsevier Science, Oxford, 1996. 

From the assemblies of fused five- and six-membered rings identifiable on the surface of 1, corannulene (8) is the smallest fragment that retains a bowl-shaped conformation. However, there are other known hydrocarbons that adopt bowl (or... 

As we prcx eed further with the process of generating hydrocarbons from carbon frameworks represented on the buckminsterfullerene surface, we encounter a new class of compounds known as semibuckminsterfullerenes. These Cjq hydrocarbons (Figure 5), which we will also refer to as buckybowls , represent one-half of the buckminsterfullerene Cgo surface, and share several common characteristics including 30 sp carbon frameworks consisting of multiple fused five- and six-membered rings and bowl-shaped geometries. 

Tricyclic Systems Central Carbocyclic Ring with Fused Five- and Six-membered Rings... 

Other Four Heteroatoms 2 2 Five or More Heteroatoms Tricyclic Systems Central Carbocyclic Ring with Fused Five-membered Rings Tricyclic Systems Central Carbocyclic Ring with Fused Five- and Six-membered Rings Tricyclic Systems Central Carbocyclic Ring with Fused Six-membered Rings... 

The steric course of the cpoxidation of monocyclic and fused five- and six-membered ring systems is largely covered by an excellent review61. A large number of examples given there have been screened for parametrization of the force field described in Section 4.5.1.1.1. some of these examples are given in Table 1. Stereochemical analyses ofepoxidation of some selected five- to 14-membered ring systems will be presented in this section. 

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