Question

The following structure is an anion with three possible resonance contributors. One incomplete resonance form is shown below. Complete the given structure by adding nonbonding electrons and formal charges. Draw the two remaining resonance structures (in any order), including nonbonding electrons and formal charges.

Answer 1

Concepts and reason

To draw the resonance structure of the given compound, delocalize the $\pi$ electrons and the lone pair of electron either towards the electron deficient species or towards the more electronegative atom.

Formal charge on the atom can be calculated by knowing the valence electron, bonding electrons, and nonbonding electrons present on the atom.

Fundamentals

Resonance structure can be drawn by the delocalization of $\pi$ electron and lone pair of electrons present in a system. Resonance structures are shown by double headed arrow. The delocalization of $\pi$ electron and lone pair in a molecule lowers the resonance energy and thus, the molecule is stabilized.

Consider the following example for drawing the resonance structure by delocalization of lone pair and double bond as shown by curved arrows:

The formal charge can be calculated by the following formula:

${\rm{Formal}}\,{\rm{charge}} = V - N - \frac{B}{2}$

Here, V is valence electrons in neutral atom; N is the number of nonbonding electrons, and B the number of bonding electrons present in an atom.

Draw the complete resonance form of the given structure by drawing the lone pair and adding the formal charge as shown below:

The formal charge present atoms are calculated as shown below:

$\begin{array}{c}\\{\rm{Formal}}\,{\rm{charge}}\,{\rm{on O atom}} = 6 - 4 - \frac{4}{2}\\\\ = 0\\\end{array}$

$\begin{array}{c}\\{\rm{Formal}}\,{\rm{charge}}\,{\rm{on S atom}} = 6 - 6 - \frac{2}{2}\\\\ = - 1\\\end{array}$

$\begin{array}{c}\\{\rm{Formal}}\,{\rm{charge}}\,{\rm{on N atom}} = 5 - 0 - \frac{8}{2}\\\\ = 5 - 1\\\\ = + 1\\\end{array}$

$\begin{array}{c}\\{\rm{Formal}}\,{\rm{charge}}\,{\rm{on carbon atom}} = 4 - 2 - \frac{6}{2}\\\\ = 4 - 5\\\\ = - 1\\\end{array}$

Therefore, the formal charge present on O is $0$ , on N is $+ 1$ , on S is $- 1$ , and on C is $- 1$ .

Draw the resonance structure of the given compound by delocalization of lone pair and $\pi$ electrons as shown below:

Ans:

Thus, the two remaining possible resonance structures of the given compound is shown below: