Resonance - UNSOLVED PRACTICE SET

Q7. Define resonance. What is a resonance hybrid?

Q8. Draw the resonance structures of:

(a) Ozone (O₃)

(b) Carbonate ion (CO₃²⁻)

Q9. Why do all C-O bonds in CO₃²⁻ have equal length, even though individual resonance structures show one double and two single bonds?

Q10. What is the difference between resonance and tautomerism?

Q11. Your art teacher shows you a painting that looks different when viewed from the left and from the right, but the actual painting is a blend of both perspectives. She says this is like resonance in chemistry. Explain how individual resonance structures are like the two views, and the resonance hybrid is like the actual painting.

Q12. Draw the resonance structures of benzene (C₆H₆) and explain why all C-C bond lengths are equal. 

Q13. Explain the concept of resonance with suitable examples. What are the essential conditions for resonance? Draw the resonance structures for:

(a) Nitrate ion (NO₃⁻)

(b) Sulphur dioxide (SO₂)

Explain how resonance affects bond lengths and bond orders in these species.

Q14. Discuss the difference between resonance and mesomeric effect. How does resonance lead to stabilization of molecules? Explain with the examples of:

(a) Carboxylate ion (RCOO⁻)

(b) Amide group (R-CONH₂)

Why is the amide nitrogen less basic than an amine nitrogen?

Q15. During a chemistry seminar, a student presents the following cases:

(a) For CO₂, two resonance structures can be drawn: O=C=O and two equivalent structures with formal charges. Why is the first structure the major contributor, and what is the actual bond order of each C-O bond?

(b) For the nitrite ion (NO₂⁻), draw the resonance structures and calculate the bond order. Why are both N-O bonds equal in length?

(c) The peptide bond in proteins (—CO—NH—) has partial double bond character due to resonance. Explain how this resonance affects the geometry of the peptide bond and why it is planar.

(d) Why does resonance not occur in H₂O or CH₄? What structural requirement must be met for resonance to be possible?

Q16. Calculate the bond order for each bond in the following species using resonance concepts:

(a) O₃ (ozone): Two resonance structures with one O=O and one O-O bond each

(b) CO₃²⁻ (carbonate): Three equivalent resonance structures

(c) NO₂⁻ (nitrite): Two equivalent resonance structures

(d) C₆H₆ (benzene): Two Kekulé structures

For each, show your calculation and explain why the experimental bond length differs from pure single or double bonds.

Q17. The nitrate ion (NO₃⁻) has three equivalent resonance structures.

(a) Draw all three resonance structures.

(b) Calculate the formal charge on each atom in one resonance structure.

(c) Calculate the average N-O bond order in NO₃⁻.

(d) Compare this bond order with the N-O bond order in NO₂ (nitrogen dioxide, which has a different structure). Explain the difference.

Q18. Consider the following molecules and their resonance stabilization:

(a) For the allyl cation (CH₂=CH-CH₂⁺), draw the resonance structures and calculate the charge distribution. How does resonance stabilize this carbocation?

(b) For the phenoxide ion (C₆H₅O⁻), draw resonance structures showing how the negative charge is delocalized into the benzene ring. Why is phenol more acidic than ethanol?

(c) The pKa of acetic acid (CH₃COOH) is 4.76, while the pKa of formic acid (HCOOH) is 3.75. The methyl group in acetic acid is electron-donating. Explain how this affects resonance stabilization of the carboxylate ion.

(d) In pyrrole (C₄H₅N), the lone pair on nitrogen participates in resonance with the ring. Draw the resonance structures and explain why pyrrole is much less basic than a typical amine.