Cyanate , resonance structure

C09-0108. Carbon, nitrogen, and oxygen form two different polyatomic ions cyanate ion, NCO, and isocyanate ion, CNO". Write Lewis stmctures for each anion, including near-equivalent resonance structures and indicating formal charges. 

Now that we have determined that structure I is correct for the cyanate ion, we still need to consider resonance structures. In keeping with the rules given earlier, the acceptable resonance structures that can be devised are... 

Write three resonance structures for (a) the cyanate ion (NCO ) and (b) the isocyanate ion (CNO ). In each case, rank the resonance structures in order of increasing importance. 

Here are the formal charges and oxidation numbers for the three cyanate ion resonance structures ... 

In contrast to the cyanate ion (NCO ), which is stable and found in many compounds, the fulminate ion (CNO ), with its different atom sequence, is unstable and forms compounds with heavy metal ions, such as Ag and Hg " ", that are explosive. Like the cyanate ion, the fulminate ion has three resonance structures. Which is the most important contributor to the resonance hybrid Suggest a reason for the instability of fulminate. 

Draw resonance structures for the ethanoate ion, CH3COO and the cyanate ion, NC0 . Both ions are resonance hybrids of two resonance structures. 

All the resonance structures for fulminate involve greater formal charges than in cyanate, making fulminate more reactive (less stable). 53. 32 kg bacterial tissue... 

For all three the cyanate group would be expected to be linear. Expected values of the H—N—C bond angle (unstrained) are 116° for A, 108° for B, and 180° for C (Sec. 4-8). Resonance among the three structures would lead to an averaged value of this angle. (The fourth structure, like A but with the double bond in the alternative planes, is not considered because it does not provide a bond orbital for the N—H bond.)... 

The percentages of the three principal resonance hybrid structures of the cyanate ion are given in Table X. Nelson and Nelson [557) studied the effect on von and vco as the force constants are altered by including progressively increasing contributions from, first, the resonance form N=C—0 and, second, "N—C=0 their results in the former case are repeated in Table XIII The calculations were... 

Assign formal charges to each atom in the resonance forms of the cyanate ion (OCN ). Which resonance form is likely to contribute most to the correct structure... 

The sum of all formal charges for each structure is -1, as it should be for a 1 - ion. Structures A and B have the least amount of formal charge and are therefore to be preferred over structure C. Structure A is preferable to B because it has the negative formal charge on the more electronegative atom. You therefore expect structure A to make the biggest contribution to the resonance forms of the cyanate ion. 

The cyanate ion (OCN") and the fulminate ion (CNO ) share the same three atoms but have vastly different properties. The cyanate ion is stable, while the fulminate ion is unstable and forms explosive compounds. The resonance stractures of the cyanate ion were explored in Example 9.8. Draw Lewis structures for the fulminate ion—including possible resonance forms—and use formal charge to explain why the Mminate ion is less stable (and therefore more reactive) than the cyanate ion. 

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