Question

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

• A. $CHF_3$
• B. $CHI_3$
• C. $CHCl_3$
• D. $CHBr_3$

Answer 1

Answer: (A)

$CHF_3$

Answer 2

Due to stronger-$I$-effect of $F$ than that of $Cl, CHF_3$ should be more acidic than $CHCl_3 .$ But actually reverse is true. This is due to : $CCl^{3-}$ left after the removal of a proton from $CHCl_3$ is stabilised due to presence of d-orbitals in $Cl$ than: $CF _{3}^{-}$ left after the removal of a proton from $CHF _{3}$ which is not stabilised due to the absence of d-orbitals on $F$.