Q40. - Organic Chemistry

Question

Question: Assign formal charges to each N and O atom in the given molecules. All lone pairs have been drawn in.

                                             a.

  

                                              b.

                                               c.

                                               d.

Step-by-Step Solution

Answer

Answer

 

a. -1

 

b. -1, +1, -1 (from left to right)

 

c. +1

 

d. 0, 0 (N and O, 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

. The calculation of the formal charge of N is as follows:

• The total number of valence electrons of nitrogen is five.
• The lone pair of electrons is four.
• The bonding pair of the electrons is four as all the N electrons are used.

 

Therefore,

$\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{N} & =& 5-4-\frac{1}{2}\times 4\\ & =& 5-4-2\\ & =& -1\end{array}$

Hence, the formal charge of N is -1.

 

 

b. The calculation of the formal charge for N (extreme left) is as follows:

• The total number of valence electrons of N is five.
• The lone pair of electrons is four.
• The bonding pair of the electrons is four as all the N electrons are used.

 

Therefore,

 $\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{N} & =& 5-4-\frac{1}{2}\times 4\\ & =& 5-4-2\\ & =& -1\end{array}$

 

Hence, the formal charge of N is -1.

 

The calculation of the formal charge for N (middle) is as follows:

• The total number of valence electrons of N is five.
• The lone pair of electrons is zero.
• The bonding pair of the electrons is eight as all the N electrons are used.

 

Therefore,

 $\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{N} & =& 5-0-\frac{1}{2}\times 8\\ & =& 5-0-4\\ & =& 1\end{array}$

 

Hence, the formal charge of N is +1.

 

The calculation of the formal charge for N (extreme right) is as follows:

• The total number of valence electrons of N is five.
• The lone pair of electrons is four.
• The bonding pair of the electrons is four as all the N electrons are used.

 

Therefore,

 

 $\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{N} & =& 5-4-\frac{1}{2}\times 4\\ & =& 5-4-2\\ & =& -1\end{array}$

Hence, the formal charge of N is -1.

 

 

c. The calculation of the formal charge for O is as follows:

• The total valence electrons of O are six.
• The lone pair of electrons is two.
• The bonding pair of the electrons is six as all the O electrons are used.

 

Therefore,

  $\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{O} & =& 6-2-\frac{1}{2}\times 6\\ & =& 6-2-3\\ & =& +1\end{array}$

 

Hence, the formal charge of O is +1.

 

 

d. The calculation of the formal charge for N is as follows:

• The total valence electrons of N are five.
• The lone pair of electrons is two.
• The bonding pair of the electrons is six as all the N electrons are used.

 

Therefore,

 $\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{N} & =& 5-2-\frac{1}{2}\times 6\\ & =& 5-2-5\\ & =& 0\end{array}$

 

Hence, the formal charge of N is zero.

 

The calculation of the formal charge for O is as follows:

• The total valence electrons of O are six.
• The lone pair of electrons is four.
• The bonding pair of electrons is four as all the N electrons are used.

 

Therefore,

$\begin{array}{rcl}\mathrm{Formal} \mathrm{charge} \mathrm{of} \mathrm{O} & =& 6-4-\frac{1}{2}\times 4\\ & =& 6-4-2\\ & =& 0\end{array}$ 

 

Hence, the formal charge of O is zero.