Exams › JEE Advanced › Chemistry

In which of the following pairs does the first species have greater resonance (delocalization) energy than the second?

1. a conjugated triene and benzene
2. a conjugated diene anion and cyclopentadienyl cation
3. a conjugated enamine and a conjugated aminoalkene
4. None of these

Correct answer: None of these

Solution

Benzene is aromatic (6 pi electrons, 4n+2) and has much larger resonance energy than an open-chain conjugated triene, so the first < second in pair 1. The cyclopentadienyl cation is anti-aromatic/non-aromatic but the comparison still does not make the open diene anion larger in a clean way; and 'enamine' vs 'aminoalkene' describe essentially the same delocalized N-C=C system, so neither is clearly greater. In none of the pairs is the first species reliably higher in resonance energy, so the answer is 'None of these'.

Related JEE Advanced Chemistry questions

• When N₂ is converted to N₂⁺, what happens to the bond dissociation energy of the N–N bond, and when O₂ is converted to O₂⁺, what happens to the bond dissociation energy of the O–O bond?
• In which of these ions is pπ–dπ bonding absent?
• What is the VSEPR formula for the chlorine trifluoride molecule?
• Consider the following molecules: CO2, SO2, and H2O. Arrange them in ascending order of their dipole moments.
• Which of the following occurrences is primarily influenced by hydrogen bonding?
• When two 1s atomic orbitals (one from each atom) combine to form molecular orbitals, which of the following statements is correct?

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →