# In the nitration, why fluorobenzene has less products in the ortho position than Clorobenzene?

Is it because, due to the eletronegativity of Fluorine, his mesomeric effect will be less pronounced, which means the electronic density will be lower, than for the clorobenzes, in the ortho positions?

• Mesomeric effect of fluorine is stronger. However, flourine has a stronger inductive effect too and its ortho position is more severly deactivated than chlorine's. Apr 5 '17 at 6:31
• Halogens — though deactivating groups — are ortho-para directing. The inductive effect reduces the electron density at ortho position more than in the para position (inductive effect varies with distance). As fluorine is more electronegative than chlorine, you will get less ortho products with fluorine than with chlorine. Apr 5 '17 at 14:39

Halogens are deactivating groups even though they show $+M$ mesomeric effect. The inductive effect is stronger than mesomeric effect. As the halogens show $-I$ inductive effect, they are deactivating groups.
When it comes to selectivity, the mesomeric effect plays a role. As the halogens show $+M$ mesomeric effect, the resonance structure has higher electron density at ortho and para positions. Therefore, halogens are ortho-para directing.