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Chemistry · Glossary

What is Directing groups?

Also known as: activating group · deactivating group · ortho/para director · meta director

Definition 22.7 University Chemistry — Year 2 · Chapter 22 — Aromaticity and Electrophilic Aromatic Substitution

A substituent on a benzene ring is an activating group if the ring reacts faster than benzene, a deactivating group if it reacts more slowly. It is an ortho/para director if the new group enters mainly at the positions next to it and opposite to it, a meta director if it enters mainly at the positions once removed.

Wheland intermediates for attack para to a substituent. With methoxy, a lone pair of oxygen shares the positive charge (an extra resonance structure, all atoms with an octet): the intermediate is stabilised, the substituent is activating and ortho/para directing. With nitro, one structure places the positive charge on the carbon bearing the electron-withdrawing group: the intermediate is destabilised, and attack goes meta.
Wheland intermediates for attack para to a substituent. With methoxy, a lone pair of oxygen shares the positive charge (an extra resonance structure, all atoms with an octet): the intermediate is stabilised, the substituent is activating and ortho/para directing. With nitro, one structure places the positive charge on the carbon bearing the electron-withdrawing group: the intermediate is destabilised, and attack goes meta.
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