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Arrange the following in the correct order of their acidic strength
$\begin{array}{cccc}\mathrm{H}_2 \mathrm{C}=\mathrm{CH}_2 & \mathrm{CH} \equiv \mathrm{CH} & \mathrm{CH}_3-\mathrm{C} \equiv \mathrm{CH} & \mathrm{CH}_3-\mathrm{CH}_3 \\ \text { I } & \text { II } & \text { III } & \text { IV }\end{array}$
Options:
$\begin{array}{cccc}\mathrm{H}_2 \mathrm{C}=\mathrm{CH}_2 & \mathrm{CH} \equiv \mathrm{CH} & \mathrm{CH}_3-\mathrm{C} \equiv \mathrm{CH} & \mathrm{CH}_3-\mathrm{CH}_3 \\ \text { I } & \text { II } & \text { III } & \text { IV }\end{array}$
Solution:
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Verified Answer
The correct answer is:
IV $ < $ I $ < $ III $ < $ II
Acidic strength $\alpha \%$ s-character.
Due to maximum \% s-character of ethyne $(50 \%)$, hydrogen atoms attached to sp hybridised carbon of ethyne are most acidic followed by those attached to $\mathrm{sp}^2$ hybridised carbon of ethene $(33 \%)$ and those attached to $\mathrm{sp}^3$ hybridised carbon of ethane $(25 \%)$
In case of propyne, acidic character decreases than that of ethyne due to $+\mathrm{I}$ effect.
Hence, order of acidic strength is:
Due to maximum \% s-character of ethyne $(50 \%)$, hydrogen atoms attached to sp hybridised carbon of ethyne are most acidic followed by those attached to $\mathrm{sp}^2$ hybridised carbon of ethene $(33 \%)$ and those attached to $\mathrm{sp}^3$ hybridised carbon of ethane $(25 \%)$
In case of propyne, acidic character decreases than that of ethyne due to $+\mathrm{I}$ effect.
Hence, order of acidic strength is:
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