Exams › JEE Main › Chemistry
Among the following species, which one is the least stabilized by resonance (has the smallest resonance/delocalization energy)?
- Benzene
- Furan (the five-membered ring containing one oxygen atom and two C=C double bonds)
- Pyridine
- A 4,4-disubstituted cyclohexa-2,5-dien-1-one (a non-aromatic cross-conjugated dienone)
Correct answer: A 4,4-disubstituted cyclohexa-2,5-dien-1-one (a non-aromatic cross-conjugated dienone)
Solution
Benzene (~36 kcal/mol), pyridine and furan are all aromatic ring systems with substantial resonance energies (furan's is lower than benzene's, ~16 kcal/mol, but still significant aromatic stabilization). The 4,4-disubstituted cyclohexa-2,5-dienone has a tetrahedral (sp3) carbon at C-4 that interrupts the cyclic conjugation, so the ring is NOT aromatic; it is only a cross-conjugated dienone whose delocalization energy is much smaller than that of the three aromatic systems. Hence it is the least resonance-stabilized.
Related JEE Main Chemistry questions
- Although the electronegativity gap between N and F is larger than that between N and H, ammonia has a dipole moment of 1.5 D while nitrogen trifluoride has only 0.2 D. The reason is that
- When N₂ is converted into N₂⁺, the dissociation energy of the N–N bond ______, and when O₂ is converted into O₂⁺, the dissociation energy of the O–O bond ______.
- From the ions listed below, which pair has geometries that can be accounted for by the same type of orbital hybridization? NO₂⁻, NO₃⁻, NH₂⁻, NH₄⁺, SCN⁻
- Atoms A and B have electronegativities of 1.20 and 4.0, respectively. What is the percentage ionic character of the A–B bond?
- In the phosphate ion, PO₄³⁻, what is the formal charge on an oxygen atom that is singly bonded to phosphorus in a P–O bond?
- Among the following species, which one has no unpaired electrons?
⚔️ Practice JEE Main Chemistry free + battle 1v1 →