Number of electrophilic centres in the given compound is _______________.

Solution

Chemistry ma’am · 3 steps

Find carbons a pull of electrons leaves short: the carbonyl, its conjugated alkene and the nitrile.

1. What to look for. An electrophilic centre is an electron-poor atom that a nucleophile can attack. In organic molecules this is usually a carbon on a polar multiple bond to a more electronegative atom, or a carbon that feels that pull through conjugation.

   Site	Why it is electron poor	Electrophilic?
   Carbonyl carbon of C=O	O pulls the π electrons, so C carries δ+	Yes
   β-carbon of -CH=CH-CO⁻	The resonance form C⁺-C=C-O⁻ puts a positive charge here	Yes
   Nitrile carbon of -C≡N	N pulls the electrons of the triple bond, so C carries δ+	Yes
   Naphthalene ring carbons	Electron-rich aromatic π cloud	No (nucleophilic)
   CH₃ and CH₂ carbons	Saturated, no polar multiple bond on them	No

2. The hidden one. The C=C is conjugated with the C=O, so the carbonyl pulls electrons through the double bond. The far end, the β-carbon, becomes electron poor. This is why nucleophiles add there in conjugate (Michael) addition.
3. So. The carbonyl carbon, the β-carbon and the nitrile carbon make 3 electrophilic centres.

The common slip: 2. Counting only the carbonyl and nitrile carbons gives 2. The β-carbon of the α,β-unsaturated ketone is also electrophilic by resonance.

The idea to keep. Every polar C=O or C≡N carbon is electrophilic. If a C=C is conjugated with C=O, its β-carbon is electrophilic too, so count it.

Answer from the NTA final answer key. Solution by PrepWiser.