Acetylenic hydrogens are acidic because

MCQ

✓
Sigma electron density of $ C-H$ bond in acetylene is nearer to carbon, which has $50\%$ $s-$character
B
Acetylene has only one hydrogen on each carbon
C
Acetylene contains least number of hydrogens among the possible hydrocarbons having two carbons
D
Acetylene belongs to the class of alkynes with molecular formula ${C_n}{H_{2n - 2}}$

✓

Answer

Correct option: A.

Sigma electron density of $ C-H$ bond in acetylene is nearer to carbon, which has $50\%$ $s-$character

a
The formation of $C - H$ bond in acetylene involves $sp$-hybridised carbon atom. Since $s$-electrons are closer to the nucleus than $p$ electrons, $sp$ hybrid orbitals are more electronegative through its smaller(in length) and thicker lobes which increases the time spent by electrons near nucleus than in $sp ^2$ and $sp ^3$. Thus, the electrons present in a bond having more $s$-character will be more closer to the nucleus. In alkynes ( $\equiv C - H )$ bond, $s$- character is $50\, \%$, the electrons constituting this bond are more strongly bonded by the carbon nucleus. Thus, acetylenic $C$-atom becomes more electronegative in comparison to $sp ^2, sp ^3$ and hence the hydrogen atom present on carbon atom $(\equiv C - H )$ can be easily removed.

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