Q30 / 125 · BITSAT 2013 · Chemistry

Which of the following is less acidic among the given halogen compounds?

  • Correct answer
    A
    $\mathrm{CHF}_{3}$
  • B
    $\mathrm{CH}_{3}$
  • C
    $\mathrm{CHCl}_{3}$
  • D
    $\mathrm{CHBr}_{3}$

Solution

Due to stronger-I-effect of $\mathrm{F}$ than that of Cl, $\mathrm{CHF}_{3}$ should be more acidic than $\mathrm{CHCl}_{3} .$ But actually reverse is true. This is due to : $\mathrm{CCl}_{3}^{-}$ left after the removal of a proton from $\mathrm{CHCl}_{3}$ is stabilised due to presence of $d$ -orbitals in Cl than: $\mathrm{CF}_{3}^{-}$ left after the removal of a proton from $\mathrm{CHF}_{3}$ which is not stabilised due to the absence of $d$ -orbitals on $\mathrm{F}$.

Hence, the correct answer is option: 'A'.

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