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 = 4 : compounds (a), (b), (c) and (h).
(a) 1H-pyridin-4-one tautomerises to 4-hydroxypyridine (aromatic pyridine ring).
(b) and (c) are cyclohexadienones; each tautomerises to phenol (aromatic).
(h), the mono-oxime of p-benzoquinone, tautomerises to 4-nitrosophenol (aromatic).
The rest fail : (d) p-benzoquinone has no sp3 alpha C-H and shows no keto-enol tautomerism; (e) cyclohex-2-en-1-one enolises only to a non-aromatic dienol; (f) cyclobut-3-en-1-one would give hydroxycyclobutadiene - anti-aromatic, not aromatic; (g) 4,4-dimethylcyclohexa-2,5-dien-1-one cannot aromatise because C-4 bears two methyls (no H, and it cannot become an sp2 benzene carbon).
