Question 24.4: Following the curved arrows, draw a resonance structure for ...
Following the curved arrows, draw a resonance structure for the \text{HCONH}^– ion.
Strategy Move electron pairs as indicated by the curved arrows, and calculate formal charges to reposition the negative charge.
Setup To determine the formal charge, we must first calculate the number of valence electrons on the atoms in question. The \text{O} and \text{N} atoms have six and five valence electrons, respectively.
Repositioning electron pairs as directed by the curved arrows gives
The formal charge on \text{N}, which had been –1, is now [5 – (3 + 2)] = 0. The formal charge^* on \text{O}, which had been 0, is now [6 – (1 + 6)] = –1. Thus, the negative charge now resides on the oxygen atom.
^*Student Annotation: Recall that formal charge is equal to valence electrons − associated electrons [≪ Section 6.4]