Which one of the following is most reactive towards electrophilic reagent?
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Answer
(2) [figure]
Solution
Reactivity towards electrophiles increases with the electron density that the substituent releases into the ring (+R effect).
–OH is the strongest ring activator here: its lone pair is freely donated to the ring.
–OCH3 is a slightly weaker activator than –OH.
–NHCOCH3: the N lone pair is also delocalised over the C=O group, so it activates much less.
–CH2OH is attached through carbon and has no lone pair to donate; it does not activate the ring by resonance.
o-Cresol (option 2) is the most reactive towards an electrophilic reagent.
Answer: (2)