Predict the direction of the following equilibrium and the approximate value of Keq.
$C H_{3} Li$ + $HC \equiv CH$ $⇌$ $C H_{4}$ + $LiC \equiv CH$ ( $p K_{a}$ : terminal alkyne = 25, $C H_{4}$ = 50)

Question

Predict the direction of the following equilibrium and the approximate value of Keq. C H 3 ​ Li + HC ≡ CH ⇌ C H 4 ​ + LiC ≡ CH ( p K a ​ : terminal alkyne = 25, C H 4 ​ = 50)

TestHub · Accepted Answer

The acid on the left is the terminal alkyne ( p K a ​ 25) and the acid on the right is methane ( p K a ​ 50). Methane is the far weaker acid, so the equilibrium lies essentially completely to the right : methyl lithium deprotonates acetylene instantly. Keq ≈ 1 0 50 − 25 = 1 0 25 ⋅

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