Answer to Question #313748 in Organic Chemistry for swarnajeet kumar

Question

What do you understand by ortho and para-directing activator? Explain with the help of a suitable example.

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