Among the following, the compound having conjugated double bonds is:

Solution & Explanation

Concept: A conjugated diene has its two C=C double bonds separated by exactly ONE single bond, giving alternating double–single–double bonds and an overlapping p-orbital (π) system. If the double bonds are separated by two or more sp³ (–CH₂–) carbons, they are ISOLATED (non-conjugated). Check each heptadiene (7-carbon chain, locants name the first carbon of each C=C): • hepta-1,3-diene: C=C at 1–2 and 3–4, separated only by the C2–C3 single bond → alternating → CONJUGATED. • hepta-1,4-diene: 1–2 and 4–5, separated by one sp³ carbon (C3) → isolated. • hepta-1,5-diene: 1–2 and 5–6, separated by two sp³ carbons → isolated. • hepta-1,6-diene: 1–2 and 6–7, the two ends of the chain → isolated. Only hepta-1,3-diene has the double bonds conjugated. Answer A. Trap: do not be misled by the gap in locant numbers alone; conjugation needs the 1,3-relationship (double bonds on alternate single bonds).