Question

Why is cl in chlorobenzene ortho and para directing to electrophilic substitution?

Answer 1

In aromatic electrophilic substitution rxn. wheather a group o-&p-directing or m-directing can easily be investigated by comparing the stability of “sigma-complex” or ‘Whealnd Complex’ for electrophilic attack at o-,p-& m-positions. If, after o-/p-attack the produced sigma complex become more stable than that of m-attack, then, in that case, that particular group is o-&p-directing ; reverse is true for m-directing groups.

Now, if you draw corresponding sigma-complexes for o-,p- & m-attack for chlorobenzene, you can see o- & p-attack yield more stable sigma complex than that of m-attack.

One thing, sometimes people think,if they just try to find where is the more electronic site, I mean o-/m-/p-position…they can easily said wheather a group is ortho-para or meta directing, then they didn't deal with — NO , —CH=CH–CO2H etc. groups. So, the best theorytical method is what I explain above.

Answer 2

because of the strong bond atraction