Question

For each of these ions, draw the important resonance forms and predict which resonance form is likely to be the major contributor.

Short answer

Themajor contributing forms are given below.

(a)

(b)

(c)

(d)

(e) All structures are equivalent.

(f)

Step-by-step solution

The important resonance forms and the major contributor in part (a).

Structure 7 is a major resonance contributor as it contains carbon with an octet and less no of an element with charges and hence more stable.

The important resonance forms and the major contributor in part (b).

Structure 3 is a major resonance contributor as it contains more electronegative oxygen with a negative charge in other structure carbon, less electronegative contains negative charge.

The important resonance forms and the major contributor in part (c).

Structure 1 is a major resonance contributor as it contains more electropositive carbon with a positive charge and less electropositive nitrogen with no charge.

The important resonance forms and the major contributor in part (d).

Structure 1 is a major resonance contributing structure as only one charge oxygen is available and no oxygen with a positive charge.

The important resonance forms and the major contributor in part (e).

All structures are equivalent as resonance contributors.

The important resonance forms and the major contributor in part (f).

In structure 3, more electronegative nitrogen possesses a negative charge and so is a major resonance contributor.

Conclusion

Negative charge on electronegative species is more favourable than on the electropositive species to determine the major contributing resonance structures.