Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

Compound (a), benzene-1,3-diol (resorcinol), exhibits easy keto-enol tautomerism. Its diketo tautomer, cyclohex-5-ene-1,3-dione system, is a reasonable beta-diketone arrangement - resorcinol even shows ketone-like reactions (for example with hydroxylamine and with ammonia) - because the loss of aromatic resonance energy is partly counterbalanced by the formation of two $\mathrm{C}=\mathrm{O}$ bonds. Compound (b), benzene-1,2-diol (catechol), would have to place the two $\mathrm{C}=\mathrm{O}$ groups on adjacent carbon atoms in its diketo tautomer - a very unstable arrangement - so its tautomerism is not observed easily. Hence (a).