In 5-membered aromatic heterocycles like pyrrole and furan, electrophilic substitution preferentially occurs at the C-2 () position rather than the C-3 () position. Which of the following statements c

Question

In 5-membered aromatic heterocycles like pyrrole and furan, electrophilic substitution preferentially occurs at the C-2 ($\alpha$) position rather than the C-3 ($\beta$) position. Which of the following statements correctly explain this regioselectivity?

Prashant Kotian · Accepted Answer

Correct answer: A,C. Electrophilic attack at C-2 of pyrrole/furan generates an intermediate with three delocalized resonance structures, spreading the positive charge over three atoms. Attack at C-3 generates an intermediate with only two resonance structures. Hence, C-2 attack is preferred. In both cases, the most stable resonance contributor involves the heteroatom donating its lone pair to form a double bond, giving every atom (except H) a complete octet.

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