Q39. - Organic Chemistry

Question

Question: Assign formal charges to each carbon atom in the given species. All lone pairs have been drawn in.

a.

b.

c.

d.

Step-by-Step Solution

Answer

Answer

 

a. 0 and -1, respectively

 

b. 0

 

c. 0

 

d. 0 and +1, respectively

Step-by-Step Solution Step 1: Determination of formal charge

The determination of formal charge is completed by using the given formula:

$\mathbf{Formal}\mathbf{ }\mathbf{charge}\mathbf{ }\mathbf{=}\mathbf{ }\left(\mathrm{valence} e^{-}\right)\mathbf{-}\left(\mathrm{lone} \mathrm{pair} \mathrm{of} e^{-}\right)\mathbf{-}\left(\frac{1}{2}\times \mathrm{bonding} \mathrm{pair} \mathrm{of} e^{-}\right)$

Step 2: Calculation of formal charge

a. The formal charge of ${\mathrm{CH}}_2$  carbon is calculated as follows:

• The total valence electrons of carbon are four.
• The number of lone pairs of electrons is zero.
• The total number of bonding pair electrons is 8 as all the carbon electrons are used.

 

Therefore,

$\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{C} & =& 4-0-\left(\frac{1}{2}\times 8\right)\\ & =& 4-4\\ & =& 0\end{array}$

Hence, the formal charge of  ${\mathrm{CH}}_2$ carbon is zero.

 

Similarly, for CH carbon, the calculation of formal charge is as follows:

• The total valence electrons of carbon are four.
• The number of lone pairs of electrons is two.
• The total number of bonding pair electrons is 6 as all the carbon electrons are used.

 

Therefore,

$\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{C} & =& 4-2-\left(\frac{1}{2}\times 6\right)\\ & =& 4-2-3\\ & =& -1\end{array}$

Hence, the formal charge of CH carbon is -1.

 

 

b. The formal charge of carbon is calculated as follows:

• The total valence electrons of carbon are four.
• The number of lone pairs of electrons is two.
• The total number of bonding pair electrons is four as all the carbon electrons are used.

 

Therefore,

$\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{C} & =& 4-2-\left(\frac{1}{2}\times 4\right)\\ & =& 4-2-2\\ & =& 0\end{array}$

Hence, the formal charge of carbon is zero.

 

 

c. The calculation of formal charge for carbon is as follows.

• The total valence electrons of carbon are four.
• The number of lone pairs of electrons is 1.
• The total number of bonding pair electrons is 6 as all the carbon electrons are used.

 

Therefore,

$\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{C} & =& 4-1-\left(\frac{1}{2}\times 6\right)\\ & =& 4-4\\ & =& 0\end{array}$

Hence, the formal charge of carbon is zero.

 

 

d. The calculation of formal charge for carbon in   is as follows:

• The total valence electrons of carbon are four.
• The number of lone pairs of electrons is zero.
• The total number of bonding pair electrons is 6 as all the carbon electrons are used.

 

Therefore,

$\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{C} & =& 4-0-\left(\frac{1}{2}\times 6\right)\\ & =& 4-3\\ & =& 1\end{array}$

Hence, the formal charge of   carbon is +1.

 

The calculation of formal charge for carbon in   as follows:

• The total valence electrons of carbon are four.
• The number of lone pairs of electrons is zero.
• The total number of bonding pair electrons is 8 as all the carbon electrons are used.

 

Therefore,

 

 $\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{C} & =& 4-0-\left(\frac{1}{2}\times 8\right)\\ & =& 4-0-4\\ & =& 0\end{array}$

Hence, the formal charge of  ${\mathrm{CH}}_3$ carbon is zero.