Consider the following three resonance forms for the cyanate ion, (OCN) 1 - . The formal charges for each atom in the formula are labeled. Based upon a formal charge analysis of each atom in the three resonance forms for the cyanate ion, OCN 1 - , rank the following three resonance forms with respect to increasing importance. (Least important to most important)

Question

Consider the following three resonance forms for the cyanate ion, (OCN) 1 - . The formal charges for each atom in the formula are labeled.  Based upon a formal charge analysis of each atom in the three resonance forms for the cyanate ion, OCN 1 - , rank the following three resonance forms with respect to increasing importance. (Least important to most important)

Quizplus · Accepted Answer

To determine the importance of resonance structures, we look at the formal charges on the atoms in each structure. Generally, structures with smaller or more evenly distributed formal charges are more important.

In structure I, the nitrogen has a formal charge of +1, which is undesirable. In structure II, the carbon has a formal charge of +1, which is also undesirable. In structure III, all atoms have formal charges of 0 or -1, which is the most desirable situation.

Therefore, we can rank the structures as follows: 
II < I < III. 
Since the question asks for increasing importance, we reverse the order to get: 
III < I < II. 
The answer is thus choice letter C.

Consider the Following Three Resonance Forms for the Cyanate Ion