Exams › JEE Main › Chemistry

Formic acid (HCOOH) can be represented as a resonance hybrid of four contributing canonical structures, labelled I, II, III and IV, that differ in the placement of the formal charges and the C=O / C-O bonds. Arrange these four contributing structures in the correct order of decreasing stability (most stable first).

1. I > II > III > IV
2. I > II > IV > III
3. I > III > II > IV
4. I > IV > III > II

Correct answer: I > II > III > IV

Solution

For a resonance hybrid, the relative weight (stability) of a canonical form follows standard rules: (1) structures with more covalent bonds and no charge separation are most stable; (2) structures with negative charge on the more electronegative atom (O) are favoured; (3) structures with complete octets are favoured; (4) structures with like-charge proximity or charge on electropositive atoms are least stable. The neutral, fully bonded Kekule form of formic acid (I) is the largest contributor, followed by the singly charge-separated forms in order of how favourably the charges are distributed, giving the order I > II > III > IV.

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 →