Question:
Acetylenic hydrogens are acidic because
Acetylenic hydrogens are acidic because
Updated On: Jun 9, 2024
- sigma electron density of C-H bond in acetylene is nearer to carbon which has 50% s-character
- acetylene has only one hydrogen on each carbon
- acetylene contains least number of hydrogens among the possible hydrocarbons having two carbons
- acetylene belong to the class of alkynes with molecular formula $C_nH_{2n-n}$
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The Correct Option is A
Solution and Explanation
Acidic character of alkynes can be explained on the basis of sp-hybridisation state of the carbon atom in alkynes. We know that an electron in
s orbital is more tightly held than in a p orbital because s-electrons are more closer to the nucleus. In sp-hybridisation, s-character is more $(50 \%)$ as
compared to $sp^2-(33 \%)$ or $sp^3-(25 \%)$ hybrid orbitals. Due to very large s-character, the electrons in sp-hybrid orbitals are held tightly by the nucleus and are quite electronegative. Consequently, the electron pair of $H-C \equiv$ bond gets displaced more towards the carbon atom and help in the release of $H^+$ ions. For a examples ethyne react with sodium metal and release the $H^+$ ions. $\hspace15mm CH \equiv CH +Na \longrightarrow HC \equiv C^- Na^+ $
s orbital is more tightly held than in a p orbital because s-electrons are more closer to the nucleus. In sp-hybridisation, s-character is more $(50 \%)$ as
compared to $sp^2-(33 \%)$ or $sp^3-(25 \%)$ hybrid orbitals. Due to very large s-character, the electrons in sp-hybrid orbitals are held tightly by the nucleus and are quite electronegative. Consequently, the electron pair of $H-C \equiv$ bond gets displaced more towards the carbon atom and help in the release of $H^+$ ions. For a examples ethyne react with sodium metal and release the $H^+$ ions. $\hspace15mm CH \equiv CH +Na \longrightarrow HC \equiv C^- Na^+ $
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