Question

Explain why the following systems are not aromatic? 

(i) 

(ii) 

(iii)  

Answer 1

(i) 

For the given compound, the number of π-electrons is 6. 

By Huckel’s rule, 

4n + 2 = 6 

4n = 4 n = 1 

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…). Since the value of n is an integer, the given compound is aromatic in nature. 

(ii) 

For the given compound, the number of π-electrons is 4. 

By Huckel’s rule, 

4n + 2 = 4 

4n = 2  n=1/2

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…), which is not true for the given compound. Hence, it is not aromatic in nature. 

(iii)

For the given compound, the number of π-electrons is 8. 

By Huckel’s rule, 

4n + 2 = 8 

4n = 6  n=3/2

For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…). Since the value of n is not an integer, the given compound is not aromatic in nature.