Which of the following compound is not aromatic?

Step-by-step solution

Aromatic compounds satisfy (4 n+2) Huckel rule. (a) 1,3 -cyclobutene Number of electrons =4 It is not equal to 4 n+2 It is not an aromatic compound (b) Pyridine Number of electrons =6(=4 n+2) (Here lone pair of electrons of N does not evolve in delocalisation) (c) Furane Number of electrons =4+2=6(=4 n+2) (d) Thiophene Number of electrons =6(=4 n+2) Thus, except 1,3 -cyclobutene, all species are aromatic in nature.