Which of the following Lewis structures is the most important (major resonance contributor) for the fulminate ion, CNO⁻?

• A. C has a single bond to N, N has a triple bond to O; formal charges: C (+1), N (0), O (-2)
• B. C has a single bond to N, N has a double bond to O; formal charges: C (0), N (+1), O (-2)
• C. C has a triple bond to N, N has a single bond to O; formal charges: C (-1), N (+1), O (0)
• D. C has a triple bond to N, N has a single bond to O; formal charges: C (0), N (+1), O (-2)

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that the most important resonance contributor is the Lewis structure with the lowest overall formal charges and the most stable arrangement of electrons, typically minimizing charges on atoms and placing negative charges on the more electronegative atoms.
2. Step 2: Calculate the formal charges for each atom in the given Lewis structures using the formula: \(\text{Formal charge} = \text{Valence electrons} - \text{Nonbonding electrons} - \frac{1}{2} \times \text{Bonding electrons}\).
3. Step 3: Compare the formal charges in each structure, noting that structures with formal charges closer to zero and negative charges on more electronegative atoms (like oxygen) are generally more stable and thus more important resonance contributors.
4. Step 4: Consider the bond orders (single, double, triple bonds) and how they affect the distribution of electrons and formal charges, ensuring that the octet rule is satisfied for each atom where possible.
5. Step 5: Identify the structure where carbon has a triple bond to nitrogen, nitrogen has a single bond to oxygen, and the formal charges are C (-1), N (+1), and O (0), as this arrangement minimizes formal charges and places the negative charge on the more electronegative oxygen, making it the major resonance contributor.