An alkene gives two moles of HCHO, one mole of CO_2 and one mole of CH_3COCHO on ozonolysis. What is its structure? [OJEE 2003]

JEE Main Chemistry question

An alkene gives two moles of HCHO, one mole of CO and one mole of CHCOCHO on ozonolysis. What is its structure? [OJEE 2003]

(A)CH=CH–CH=CH–CH (a simple conjugated diene, no allene unit)
(B)CH=C=CH–CH–CH (a simple allene, no methyl branch)
(C)CH=C=C(CH)–CH (a trisubstituted allene with only one alkene terminus)
(D)CH=C=C(CH)–CH=CHCorrect

Answer: (D)

Solution

Formation of CO on ozonolysis signals a cumulated diene (allene, C=C=C), whose central carbon bears no substituent of its own and is oxidised all the way to CO, while each flanking carbon gives its own carbonyl fragment. Two moles of HCHO come from two terminal =CH groups, and CHCOCHO (methylglyoxal)

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Question ID VK-142251