Chapter 3, Problem 3.1P

The dimethyldithiocarbamate ion, ${\left[{\text{S}}_{\text{2}}\text{CN}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\right]}^{\text{-}}$ has the following skeletal structure

a. Give the important resonance structures of this ion, including any formal charges wherenecessary. Select the resonance structure likely to provide the best description of this ion.
b. Repeat for the dimethylthiocarbamate ion, ${\left[\text{OSCN}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\right]}^{\text{-}}$ .

Interpretation Introduction

Interpretation: The most important resonance structures of ${\left[{\text{S}}_{\text{2}}\text{CN}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\right]}^{-}$ should be determined.

Concept introduction: Formula to calculate the formal charge of the atom is as follows:

  $\text{Formal}\text{charge}=\left(\begin{array}{l}\text{number}\text{of}\\ \text{valence}\\ \text{electrons}\end{array}\right)-\left(\begin{array}{l}\text{number}\text{of}\\ \text{unshared}\\ \text{electrons}\end{array}\right)-\left(\begin{array}{l}\text{number}\text{of}\\ \text{bonds to the}\\ \text{atom}\end{array}\right)$

More important resonance structure selected as follows:

1. Always prefer smaller formal charges over the larger formal charge.

2. Always prefer the different formal charges on adjacent atoms instead of the same nonzero formal charge.

3. A more negative formal charge must be located on the most electronegative atom.

Explanation of Solution

Nitrogen has five valence electrons,carbon has four valence electrons and sulfur has six valence electrons. The resonance structure of ${\left[{\text{S}}_{\text{2}}\text{CN}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\right]}^{-}$ is as follows:

  

Since structure I and II have complete octet with least negative charge that resonates on sulfur, hence, most important structures are structure I and II.

Interpretation Introduction

Interpretation: The most important resonance structures of ${\left[\text{OSCN}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\right]}^{-}$ should be determined.

Concept introduction: Formula to calculate the formal charge of the atom is as follows:

  $\text{Formal}\text{charge}=\left(\begin{array}{l}\text{number}\text{of}\\ \text{valence}\\ \text{electrons}\end{array}\right)-\left(\begin{array}{l}\text{number}\text{of}\\ \text{unshared}\\ \text{electrons}\end{array}\right)-\left(\begin{array}{l}\text{number}\text{of}\\ \text{bonds to the}\\ \text{atom}\end{array}\right)$

More important resonance structure selected as follows:

1. Always prefer smaller formal charges over the larger formal charge.

2. Always prefer the different formal charges on adjacent atoms instead of the same non-zero formal charge.

3. A more negative formal charge must be located on the most electronegative atom.

Explanation of Solution

Nitrogen has five valence electrons,carbon has four valence electrons and sulfur has six valence electrons. The resonance structure of ${\left[\text{OSCN}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\right]}^{-}$ is as follows:

  

Since structure I has complete octet with least negative charge which exists on more electronegative atom that is oxygen,hence, most important structures is structure I.