Question

Which of the following are aromatic?

Short answer

Among all the 6 compounds, compound b and f are aromatic compounds according toHückel’s rule [(4n+ 2) π electrons].

Step-by-step solution

Measurement of aromaticity

Aromaticity of a compound can be measured through theHückel’s rule, which is stated thatfor a planar, cyclic compound to be aromatic, its uninterrupted π cloud must contain (4n+ 2) π electrons, where nis any whole number. According to Hückel’s rule, then, an aromatic compound must have 2 (n= 0), 6 (n= 1), 10 (n= 2), 14 (n= 3), 18 (n= 4), and so on, π electrons.

Aromaticity of given compounds

a) For structure a, the compound is not aromatic as it has 4 electrons and according to (4n+ 2) π electrons, it can’t be satisfied with a valid n value.

b) For structure b, the compound is aromatic as it has 2 electrons and according to (4n+ 2) π electrons, it can be satisfied with a n=0 value.

c) For structure c, the compound is not aromatic as it has 4 electrons and according to (4n+ 2) π electrons, it can’t be satisfied with a valid n value.

d) For structure d, the compound is not aromatic as it has 4 electrons and according to (4n+ 2) π electrons, it can’t be satisfied with a valid n value.

e) For structure e, the compound is not aromatic as it has 4 electrons and according to (4n+ 2) π electrons, it can’t be satisfied with a valid n value.

f) For structure f, the compound is aromatic as it has 6 electrons and according to (4n+ 2) π electrons, it can be satisfied with a n=1 value.