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Chemistry · 2025 · 4 marks
CBSE 2025 · Region 1 · Set 2 · Q29
Phenols undergo electrophilic substitution reactions readily due to the strong activating effect of OH group attached to the benzene ring. Since, the…
Phenols undergo electrophilic substitution reactions readily due to the strong activating effect of OH group attached to the benzene ring. Since, the OH group increases the electron density more to o- and p- positions therefore OH group is ortho, para-directing. Reimer-Tiemann reaction is one of the examples of aldehyde group being introduced on the aromatic ring of phenol, ortho to the hydroxyl group. This is a general method used for the ortho-formylation of phenols. Answer the following questions :
(a)
What happens when phenol reacts with
(i)
$\displaystyle \mathrm{Br}_{2} / \mathrm{CS}_{2}$
(ii)
Conc. $\displaystyle \mathrm{HNO}_{3}$
(b)
Why phenol does not undergo protonation readily?
(c)
Which is a stronger acid - phenol or cresol ? Give reason.
OR
OR
(c)
Write the IUPAC name of the product formed in the Reimer- Tiemann reaction. Tiemann reaction.
Marking-scheme solution
(a)(i)
/ $\displaystyle 2$-Bromophenol and $\displaystyle 4$-Bromophenol is
formed.
(ii)
/ $\displaystyle 2,4,6$-Trinitrophenol / Picric acid is
formed.
(b)
Due to resonance, the lone pair of electrons on oxygen is not easily available for
protonation.
(c)
Phenol
Due to electron releasing effect (+I effect) of methyl group/ phenoxide ion formed is less
stable in cresol.
(c)
$\displaystyle 2$-Hydroxybenzaldehyde / $\displaystyle 2$- Hydroxybenzenecarbaldehyde.
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