JEE PYQ: General Organic Chemistry Question 42
Question 42 - 2019 (09 Jan Shift 1)
Which amongst the following is the strongest acid?
(1) $\text{CHBr}_3$
(2) $\text{CHI}_3$
(3) $\text{CH(CN)}_3$
(4) $\text{CHCl}_3$
Show Answer
Answer: (3)
Solution
Due to the resonance stabilisation of the conjugate base, $\text{CH(CN)}_3$ is the strongest acid amongst the given compounds. $\text{CH(CN)}_3 \rightleftharpoons \text{H}^+ + \dot{\text{C}}(\text{CN})_3^-$. The conjugate bases of $\text{CHBr}_3$ and $\text{CHI}_3$ are stabilised by inductive effect of halogens. This is why they are less stable. Also, the conjugate base of $\text{CHCl}_3$ involves back-bonding between 2p and 3p orbitals.
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