Benzo-derivatives

The benzo[a] (19), benzo[/t (15) and benzo[c] (16) fused heterocycles are heterocyclic analogues of naphthalene, with the dibenzo heterocycles (17) bearing a similar electronic relationship to phenanthrene. Some of these compounds are still known by their trivial names indole (15 Z = NH), isoindole (16 Z = NH), carbazole (18) and indolizine (19). The names thianaphthene and pyrrocoline for (15 Z = S) and (19) respectively are now little used. Particular confusion can arise in consulting 

The non-aromatic isomers of indoles (15 Z = NH) are indolenines (20), which are stable only if R is not equal to H however, isoindoles often exist as (21). Some of the carbonyl derivatives have trivial names oxindole (22 Z = NH), coumarone (22 Z = 0), indoxyl (23 Z = NH) and phthalide (24 Z = 0). The common names indoline (25 Z = NH) and coumaran (25 Z = 0) are used for the 2,3-dihydro derivatives of indole and benzofuran, respectively. Similarly, isoindoline is (26, Z = NH). 

Skatole R = Me Tryptamine R = CH2CH2NH2 3-IndoIeacetic acid R = CH2CO,H 

Structure of Five-membered Rings with One Heteroatom 

Benzo derivatives show at least two, and up to seven, maxima in the range 200-320 nm (Table 24). The longest wavelength maximum occurs at 275-315 nm and generally at rather longer wavelengths for the sulfur derivatives than for their N or O analogues, and also for the benzo[c] compared with the benzo[f ] derivatives. 

X y Amax (nm) (loge) Amax (nm) (loge) Amax(nrn) (logc) 

Substituent Aza positions Substituent position Substituent position Substituent position  

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Table 11 summarizes the main results on the tautomerism of mono-hydroxy-, -mercapto-, -amino- and -methyl-azines and their benzo derivatives, in water. At first sight the equilibrium between 2-hydroxypyridine (71) and pyridin-2-one (72) is one between a benzenoid and a non-benzenoid molecule respectively (71a 72a). However, the pyridinone evidently... 

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