Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub
X = Number of compounds which undergo Tautomerisation to form an Aromatic product.
(a) 
(b) 
(c) 
(d) 
(e) 
(f) 
(g) 
(h) 
Find the value of X?
Answer:
Solution:
X = 3 : compounds (a), (c) and (h).
(a) 1H-pyridin-2-one tautomerises to 2-hydroxypyridine (aromatic pyridine ring).
(c) 3-Methylcyclohexa-2,5-dien-1-one tautomerises to 3-methylphenol (aromatic).
(h), the mono-imine of p-benzoquinone, tautomerises to 4-aminophenol (aromatic).
The rest fail : (b) cyclohex-2-en-1-one enolises only to a non-aromatic dienol; (d) naphthalene-1,4-dione has no sp3 alpha C-H on the quinone ring and shows no keto-enol tautomerism; (e) cyclohex-3-en-1-one enolises only to non-aromatic enols; (f) cyclopent-4-en-1,3-dione would give a fully conjugated 4 pi enol - anti-aromatic, not aromatic; (g) 6,6-dimethylcyclohexa-2,4-dien-1-one cannot aromatise because C-6 bears two methyls (no H, and it cannot become an sp2 benzene carbon).
