Answer to Question #84511 in Organic Chemistry for Anand

Question

What do you understand by ortho/para directing activators and meta directing deactivators?

Answer 1

Ortho, para directing groups are electron-donating groups in the reactions of electrophilis aromatic substitution. These groups have a lone pair of electrons or an electron density that “pushes” into the 6π-electron system of benzene. This leads to uneven distribution of electron density in benzene ring: electron density increses in ortho- and para-positions and electron density decreses in meta- positions.

Electrophiles are poor in electrons, they attack electron rich ortho- and para-positions in benzene.

Ortho-, para-directing groups are electron-donating groups: -O^–, -NR₂, -NH₂, -OH, -OR, -R

Electron withdrawers / deactivators have a positive charge on the substituent or a very electronegative atom attached to it, which “pulls” electrons out of the benzene.This leads to uneven distribution of electron density in benzene ring: electron density increses in meta- positions and electron density decreses in ortho and para- positions.

Meta directing groups are electron-withdrawing groups: -NO₂, -NR₃⁺ -NH₃⁺, -SO₃H, -CN, -CO₂H, -CO₂R, -COH