Organic Chemistry Basics Result Question 10
10. Which amongst the following is the strongest acid?
(2019 Main, 9 Jan I)
(a) $\mathrm{CHBr} _3$
(b) $\mathrm{CHI} _3$
(c) $\mathrm{CHCl} _3$
(d) $\mathrm{CH}(\mathrm{CN}) _3$
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Answer:
Correct Answer: 10. ( d )
Solution:
- We know, a stronger acid produces its stable or weaker conjugate base. Here, $\mathrm{CH}(\mathrm{CN})_3$ produces the most stable conjugate base $(\mathrm{NC})_3 \mathrm{C}^{-}$. Stronger $-R$ and $-I$ effects of the $\mathrm{CN}^{-}$group, make the carbanion (conjugate base) very stable. The resonance hybrid structure of $\left[(\mathrm{NC})_3 \mathrm{C}\right]$ is as follows:
However, halogen $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$ show $-I$ effect but $+R$ effect of halogens, destabilises the carbanion, $X_3 \mathrm{C}^{-}$(conjugate base of the haloform, $\mathrm{HCX}_3$ ).
Thus, $\mathrm{CH}(\mathrm{CN})_3$ is the strongest acid among the given options.
BETA
