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Which aromatic compound is more reactive towards electrophilic substitution?

  1. benzene

  2. chlorobenzene

  3. phenol

  4. toluene

Correct answer: phenol

But, according to me, the answer should be toluene.

My reason: Toluene is an ortho-para directing group as well as an electron-donating group which increases the electron density at ortho-para position and activates the aromatic ring towards electrophilic substitution.

Where I am wrong?

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  • $\begingroup$ And -OH is what? This description fits even more. $\endgroup$ – Mithoron Jun 29 '18 at 20:15
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You have to make a comparison between phenol and toluene. You have identified what toluene does, but you haven't described what phenol does.

The hydroxyl group in phenol increases electron density in the ring by resonance (+M effect). Note that the methyl group in toluene increases electron density only by hyperconjugation and inductive effect.

Resonance effects are generally far more superior to hyperconjugation. Hence, without doubt, phenol is more activated towards EAS as compared to toluene.

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    $\begingroup$ "Resonance effects are generally far more superior to hyperconjugation" - Why? $\endgroup$ – rv7 Jun 29 '18 at 11:01
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    $\begingroup$ @Rahul Resonance involves direct conjugation of an electron pair on an atom into the conjugated system. However, for hyperconjugation, you have to first break the C-H bond, and only then the lone pair on the carbon atom formed can resonate (Hyperconjugation is called "no bond resonance" if you recall) Hence, resonance activation of ring is better. $\endgroup$ – Gaurang Tandon Jun 29 '18 at 16:39

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