Arrange the following 5-membered heterocyclic aromatic compounds in decreasing order of their reacti — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

The reactivity depends on the heteroatom's ability to delocalize its lone pair and stabilize the positive charge in the arenium ion transition state ($+M$ effect). Nitrogen accommodates a positive charge more readily than oxygen (since N is less electronegative), making pyrrole highly reactive. Sulfur's $+M$ effect is weaker than oxygen's because the overlap of the larger $3p$ orbital of S with the $2p$ orbital of C is poor, making thiophene the least reactive of the three. Thus, the reactivity order is Pyrrole > Furan > Thiophene.