See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: The parent chain in IUPAC nomenclature is the longest continuous carbon chain that includes the principal characteristic group (here, the ketone C=O). Step 1: Identify the principal characteristic group. The compound contains a ketone (C=O), so the parent chain must include the carbonyl carbon. Step 2: Identify the longest carbon chain containing the ketone. The non-ring portion of the molecule is: CH3-C(=O)-CH=CH- (attached to the benzene ring). Counting these carbons: C1 (CH3) - C2 (C=O) - C3 (CH=) - C4 (=CH-). That gives 4 carbons in the chain. Step 3: Consider whether the benzene ring carbons can extend the chain. The benzene ring is treated as a substituent (phenyl group) rather than being incorporated into the parent chain, because including ring carbons would not give a simple acyclic chain and the ring is named as a phenyl substituent. Step 4: The parent chain is therefore but-3-en-2-one (4 carbons: C1=CH3, C2=carbonyl carbon, C3 and C4 are the vinyl carbons), making the compound (E)-4-phenylbut-3-en-2-one. Step 5: Count of carbons in parent chain = 4. Why other counts fail: Taking only 3 carbons would miss CH3; taking 5 or more would require including benzene ring carbons, which are part of an aromatic ring substituent, not the main chain. Therefore, the correct answer is 4.