This question involves identifying the final product (Z) of a reaction sequence. The starting compound is a cyclic ketone with a bromine substituent, and it undergoes a reaction with KOH (potassium hydroxide).

The key concept here is the Favorskii rearrangement. This rearrangement occurs when alpha-halo ketones (ketones with a halogen on the carbon adjacent to the carbonyl group) are treated with a strong base, such as KOH or an alkoxide.

Mechanism of Favorskii Rearrangement:

Step 1: The base (OH⁻) abstracts an alpha-proton from the carbon atom that is not bearing the halogen, generating a carbanion.

Step 2: This carbanion attacks the carbonyl carbon, leading to the formation of a cyclopropanone intermediate. This step involves an intramolecular nucleophilic substitution (S_N2).

Step 3: The base then attacks the cyclopropanone ring. The ring opens in a way that relieves ring strain and forms a more stable carboxylate anion. The regiochemistry of the ring opening is such that the more stable carbanion is formed (i.e., the ring breaks at the bond adjacent to the most substituted carbon).

Step 4: Protonation (if in aqueous medium) yields the final carboxylic acid product.

In this specific case, the starting compound is a symmetrical cyclic ketone (cyclopentanone) with a bromine on one of the alpha-carbons. Because the ring is symmetrical, both alpha-carbons are equivalent. The Favorskii rearrangement will contract the five-membered ring (cyclopentanone) to a four-membered ring (cyclobutanecarboxylic acid).

The final product (Z) is cyclobutanecarboxylic acid. Its structure is a cyclobutane ring with a -COOH (carboxylic acid) group attached.

Comparing with the options, the correct structure is the one showing a four-membered ring with a carboxylic acid group: Correct Option

Related Topics & Formulae

Favorskii Rearrangement: A reaction where an alpha-halo ketone, upon treatment with a base, rearranges to form a carboxylic acid (or its derivative) with a condensed carbon skeleton. It is particularly important for ring-contraction in cyclic alpha-halo ketones.

General Reaction: R-C(O)-CH₂-X + Base → R-CH₂-COOH (for acyclic). For cyclic ketones, it leads to a ring-contracted carboxylic acid.

Key Theory: The mechanism proceeds through a cyclopropanone intermediate, which is then opened by the nucleophile (the base).