Consider the five cyclic species (I to V) shown in the figure. According to Huckel's rule, how many of these species are aromatic?

Step-by-step solution

According to Huckel's rule, a species is aromatic if it is cyclic, planar, fully conjugated, and contains (4n + 2) electrons, where n is an integer ( 0, 1, 2, ). (I) Naphthalene: It is a planar, fully conjugated bicyclic system with 5 double bonds, giving 10 electrons. Since 10 = 4(2) + 2 , it is aromatic. (II) Cyclopentadienyl cation: It is a planar, fully conjugated cyclic system with 2 double bonds, giving 4 electrons. Since 4 = 4(1) , it is antiaromatic. (III) Pyrrole: It is a planar, fully conjugated cyclic sy