Question

Chlorination of Naphthalene takes place mainly at alpha position. Why ? Explain.?

Answer 1

In napthalene, attack of electrophile occurs preferably at a alpha carbon (C1 position).

Napthalene undergoes electrophilic substitution reactions similar to benzene. In naphthalene, eletrophilic substitution can occur at C1(alpha carbon) or at C2 (beta carbon). The carbocation formed by attack of electrophile at alpha-position is much more stabilized by resonance since it has four contributing structures in which aromatic character is retained in one of the ring.

 The carbocation formed by the attack of electrophile at beta-position has only two contributing structures in which aromatic character is retained in one of the rings. Thus, electrophillic substitution occurs preferably at alpha-carbon that is, C1 position.

in simple words,

The alpha position is more prone to reaction position in naphthalene because the intermediate formed becomes more stable due to more diffusion of charges through the adjacent pie electrons.

Thus resonance do have its role to play in reactivity of alpha position.



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