Select the correct statement(s). Take the pKa of water as 15.7 and of $H X_{3} O X^{+}$ as -1.7.

AIn $CH X_{3} CH X_{2} - OH X_{2} X^{+}$ the leaving group $H X_{2} O$ is much better than $OH X^{-}$ in $CH X_{3} CH X_{2} - OH$ .
B $F X^{-}$ is a better leaving group than $I X^{-}$ in $S_{N} 2$ because the C-F bond is the most polar.
C $OH X^{-}$ is a poor leaving group because its conjugate acid is weak (pKa 15.7), so alcohols are activated by protonation or by conversion to sulfonates.
D $CH X_{3} COO X^{-}$ (conjugate acid pKa 4.76) is a poorer leaving group than $CH X_{3} O X^{-}$ (conjugate acid pKa 15.5).

Answer: A, C

Water has conjugate-acid pKa -1.7 versus 15.7 for

OH X^{-}

, so protonation makes a vastly better leaving group (A true), and this is why alcohols are activated by protonation or sulfonation (C true). Leaving ability follows the weakness of the base, so

I X^{-}

beats

F X^{-}

(B false), and acetate (pKa 4.76) is a better leaving group than methoxide (15.5), making D false.

Practice Organic Reaction Mechanisms I: Nucleophiles and Carbonyl Addition More on Electrophiles, nucleophiles, nucleophilicity and leaving groups

Previous questionNext question

Select the correct statement(s). Take the pKa of water as 15.7 and of HX3​OX+ as -1.7.

Answer: A, C

More questions on Electrophiles, nucleophiles, nucleophilicity and leaving groups

Select the correct statement(s). Take the pKa of water as 15.7 and of $H X_{3} O X^{+}$ as -1.7.