See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: The Claisen Rearrangement is a [3,3]-sigmatropic rearrangement. When an aryl allyl ether is heated, it undergoes a concerted pericyclic reaction where the allyl group migrates from the oxygen to the ortho carbon of the aromatic ring, and the oxygen becomes a phenol OH. Step 1 - Identify the starting material: The starting material is phenyl cinnamyl ether: a phenol ring bearing the ether oxygen connected to -CH2-CH=CH-C6H5 (cinnamyl group, where the double bond is between C2 and C3, with a phenyl group on C3). Step 2 - Apply Claisen Rearrangement mechanism: In a [3,3]-sigmatropic shift, numbering from the oxygen: O(1)-C(2,allylic CH2)-C(3,=CH)-C(4,CHC6H5) rearranges through a chair-like six-membered transition state. The bond forms between C3 of the allyl system and the ortho carbon of the ring, while the O-C(allylic) bond breaks. The allyl group migrates with inversion (gamma carbon bonds to ortho carbon). Step 3 - Determine which carbon attaches to the ring: The gamma carbon of the cinnamyl group is the CHC6H5 carbon (C3 bearing the phenyl substituent). This carbon forms the new C-C bond to the ortho position of the phenol ring. Simultaneously the C2=C3 double bond shifts to C1=C2, giving a terminal =CH2. Step 4 - Determine the product structure: After the [3,3]-shift, a cyclohexadienone intermediate forms. Rearomatization gives an ortho-substituted phenol where the substituent at the ortho position is -CH(C6H5)-CH=CH2. This is 2-(1-phenylallyl)phenol: an ortho-hydroxyphenyl ring bearing -CH(C6H5)CH=CH2. Step 5 - Match to options: This matches option (b): ortho-OH phenol with -CH(C6H5)CH=CH2 at the ortho position. Why other options fail: - (a) shows -CH2CH=CHC6H5 at ortho position: this would be a simple O-to-ortho migration without inversion of the allyl group, which does not occur in Claisen rearrangement (inversion at gamma carbon is required). - (c) shows a phenoxy ether product with allyl group -CH2CH=CH2: this is not the Claisen product; it would require loss of the terminal phenyl group. - (d) shows a para-substituted phenol with an ethyl-bearing allyl group: incorrect regiochemistry and wrong substituents. Therefore, the correct answer is B.