See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: The Wittig reaction converts a carbonyl compound (aldehyde or ketone) into an alkene by reaction with a phosphorus ylide (Ph3P=CHR). The C=O bond is replaced by a C=C bond. Step 1: Identify the reagent. Ph3P=CH2 is methylenetriphenylphosphorane, a stabilized ylide where the carbanion carbon bears two hydrogens. Step 2: Apply the Wittig reaction mechanism. The ylide attacks the carbonyl carbon of cyclohexanone via a [2+2] cycloaddition to form a four-membered oxaphosphetane intermediate, which then undergoes retro-[2+2] elimination to give an alkene and triphenylphosphine oxide (Ph3P=O). Step 3: Determine the product. The C=O of cyclohexanone is replaced by C=CH2. Since the ylide is Ph3P=CH2 (no substituents other than H on the ylide carbon), the product is methylenecyclohexane: a cyclohexane ring with an exocyclic methylene group (=CH2) at the former carbonyl carbon. Step 4: Evaluate the options. (a) 1-methylcyclohex-2-ene: This would require migration of the double bond into the ring with a methyl group — not the direct Wittig product. (b) 3-methylcyclohex-1-ene: Similarly an endocyclic alkene with methyl group — not the Wittig product. (c) Methylenecyclohexane (cyclohexane with exocyclic =CH2): This is exactly the product of Wittig reaction between cyclohexanone and Ph3P=CH2. The C=O is replaced by C=CH2. (d) 1-(hydroxymethyl)cyclohexane: This would be a nucleophilic addition product, not a Wittig product. The Wittig reaction is highly specific: the C=O is converted to C=CH2, giving an exocyclic double bond, not an endocyclic rearranged product. Therefore, the correct answer is C.