Predict the direction of the following equilibrium and the approximate value of Keq.
$R - C \equiv C^{-}$ + $RN H_{2}$ $⇌$ $R - C \equiv C - H$ + $RN H^{-}$ ( $p K_{a}$ : amine ≈ 38, terminal alkyne = 25)

Question

Predict the direction of the following equilibrium and the approximate value of Keq. R − C ≡ C − + RN H 2 ​ ⇌ R − C ≡ C − H + RN H − ( p K a ​ : amine ≈ 38, terminal alkyne = 25)

TestHub · Accepted Answer

The acid on the left is the amine ( p K a ​ ≈ 38) and the acid on the right is the terminal alkyne ( p K a ​ 25). The amine is the much weaker acid, so the equilibrium lies far to the left : an acetylide is not basic enough to deprotonate an amine (the reverse is what happens). Keq ≈ 1 0 25 − 38 = 1 0 − 13 ⋅

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