How many following reactions is expected to occur quantitatively? (a) CH 3 − C ≡ C − H + C 2 H 5 OK → CH 3 − C ≡ CK + C 2 H 5 OH (b) CH 3 − C ≡ C − H + NaNH 2 → CH 3 − C ≡ CNa + NH 3

Question

How many following reactions is expected to occur quantitatively?

(a) $CH_{3} - C \equiv C - H + C_{2} H_{5} OK \to CH_{3} - C \equiv CK + C_{2} H_{5} OH$

(b) $CH_{3} - C \equiv C - H + NaNH_{2} \to CH_{3} - C \equiv CNa + NH_{3}$

(c) $CH_{3} - CH_{3} + NaNH_{2} \to CH_{3} - CH_{2} Na + NH_{3}$

(d) $CH_{2} = CH_{2} + NaNH_{2} \to CH_{2} = CHNa + NH_{3}$

(e)

(f) $CH_{3} - C \equiv C - H + NaH \to CH_{3} - C \equiv CNa + H_{2}$

TestHub · Accepted Answer

A proton transfer reaction occurs quantitatively only when the acid on the reactant side is stronger (lower pKa) than the conjugate acid formed.

In (b), terminal alkyne (pKa ≈ 25) is deprotonated by NH₂⁻ whose conjugate acid NH₃ has pKa ≈ 38; hence reaction proceeds forward completely.

In (f), NaH provides H⁻ and formation of H₂ gas drives the reaction strongly to completion.

In (a), C₂H₅O⁻ is not strong enough to deprotonate the terminal alkyne quantitatively.

In (c), (d), and (e), the hydrocarbons are much weaker acids, so carbanion formation is not favorable.

Therefore, only (b) and (f) occur quantitatively.

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