Question

Iodine azide,adds to alkenes by an electrophilic mechanism similar to that of bromine. If a monosubstituted alkene such as1-butene isused, only one product results:

b) Calculate formal charges for the atoms in both resonance structuresyou drew for,in part (a).

Short answer

Formal charge for both the resonance structures are:

Formal Charge

I N(i) N(ii) N(iii)

A) 0 0 +1 -1

B) 0 -1 +1 0

Step-by-step solution

Formal charge

Formal charge is an imaginary charge. In a polyatomic molecule the charge is not distributed on any single atom whereas the charge is distributed in a molecule as a whole.

Mathematical formula of formal charge is:

$F=v-\frac{s}{2}-u$

Where,

V = Number of valance electrons

S = Total shared electrons

U = Number of unshared electrons

Example

Formal charge of carbon dioxide molecule

$\mathrm{O}=\mathrm{C}=\mathrm{O}$

Formal charge of one oxygen atom = 6-2-4 = 0

Formal charge for other oxygen atom will be same i.e. 0.

Formal charge of carbon atom = 4-4-0 = 0

Calculation of formal charge of resonance structure

As we know that, Formula for calculating formal charge is:

$F=v-\frac{s}{2}-u$

By substituting the values in above formula we will calculate formal charge for both the resonance structures.

Formal charge for the atoms of resonance structure A is:

Formal charge for I atom =$7-\frac{2}{2}-6=7-1-6=0$

Formal charge for N(i) atom =$5-\frac{6}{2}-2=5-3-2=0$

Formal charge for N(ii) atom =$5-\frac{8}{2}-0=5-4-0=+1$

Formal charge for N(iii) atom =$5-\frac{4}{2}-4=5-2-4=-1$

Formal charge for the atoms of resonance structure B is:

Formal charge for I atom =$7-\frac{2}{2}-6=7-1-6=0$

Formal charge for N(i) atom =$5-\frac{4}{2}-4=5-2-4=-1$

Formal charge for N(ii) atom =$5-\frac{8}{2}-0=5-4-0=+1$

Formal charge for N(iii) atom =$5-\frac{6}{2}-2=5-3-2=0$