What a learner can do afterwards
- Classifies a substituent as activating or deactivating and as ortho and para or meta directing
- Draws the resonance forms of the intermediate to justify the directing outcome rather than reciting it
- Explains why the halogens deactivate but still direct to ortho and para
- Orders two substitutions correctly in a synthesis so that the second lands where it is wanted
1 · Read
A group already on the ring decides where the next one lands and how fast it arrives. Groups such as OH, NH2, and alkyl push electrons toward the ring, speed it up, and send newcomers to the ortho and para spots. Groups such as NO2 and carbonyl pull electrons away, slow the ring down, and send newcomers to the meta spot.
The halogens break the pattern and you must learn them as the exception. They slow the ring by pulling electrons through single bonds, yet they still direct ortho and para. Their lone pairs pour back into the intermediate by resonance and steady it, which outweighs the pulling.
Never recite a directing outcome without drawing the intermediate behind it. The electrophile adds first to give a carbocation called the arenium ion, and you draw its resonance forms for each attack site. For phenol, ortho and para attack give one form with the positive charge next to the oxygen lone pair, which steadies it, while meta attack gives no such form.
When two new groups are needed, plan the order so each group steers the next one into the wanted spot, since swapping the steps can give a different isomer. Also note that an amino group often needs protection before nitration, and Friedel Crafts reactions fail on strongly deactivated rings.
The group in place shapes the intermediate, the intermediate picks the landing spot, and the order of steps decides the final isomer.
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Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.