Question

Write the product when any electrophile attacks on 1-chloro-8-methoxynaphtalene. Explain why.

Answer 1

The halogen atom is ortho and para directing and therefore, substitution takes place at ortho and para positions giving electrophilic substitution reactions at the benzene ring. In the resonance structures of chlorobenzene the ortho and para positions get negatively charged, i.e. the electron density is relatively more at ortho and para positions. The incoming electrophile is more likely to attack these positions. But, because of steric hindrance at the ortho position, the para-product usually predominates over the ortho product. Also, the halogen atom has -I effect because it is a electron withdrawing group. As a result, it tends to deactivate the benzene ring. Therefore, the electrophilic substitution reactions of chlorobenzene occur slowly and under drastic conditions compared to benzene.

Haloarenes undergo electrophilic substitution reactions slowly as compared to benzene. Halogen group is ortho and para directing (para-product usually predominates over the ortho product). So in the above reacttion 4-Chloro benzene predominates over 2-chloro benzene.