Organic Chemistry Basics 2 Question 10
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10. Which amongst the following is the strongest acid?
======= ####10. Which amongst the following is the strongest acid?
3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed (a) $\mathrm{CHBr}_{3}$
(b) $\mathrm{CHI}_{3}$
(c) $\mathrm{CHCl}_{3}$
(d) $\mathrm{CH}(\mathrm{CN})_{3}$
(2019 Main, 9 Jan I)
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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:
Resonance hybrid structure of $\left.[\mathrm{NC})_{3} \mathrm{C}\right]$
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, $\mathrm{HC} X_{3}$ ).
Thus, $\mathrm{CH}(\mathrm{CN})_{3}$ is the strongest acid among the given options.
