Question

All the alkynes do not have acidic hydrogen, Give example of an alkyne that does not have acidic
hydrogen.
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Answer 1

Explanation:

Terminal alkynes are much more acidic than most other hydrocarbons. Removal of the proton leads to the formation of an acetylide anion, RC=C: -. The origin of the enhanced acidity can be attributed to the stability of the acetylide anion, which has the unpaired electrons in an sp hybridized orbital.

Answer 2

2-pentyne does not have acidic hydrogen.

• Alkane, alkene and alkynes are three categories based on the number of bonds between carbon.
• Alkane refers to single bond, alkene refers to double bond and alkyne has triple bond between two carbons.
• Now, the hybridization of alkane is $CH_{3} - CH_{3}$ hybridization of alkyne is $CH_{2} = CH_{2}$ and hybridization of alkyne is HC≡CH.
• Here, as evident by the chemical formula of each, the alkyne has highest s character.
• Alkane has sp³ hybridization with 25% s character and alkene has sp² hybridization with 33% s character. But, alkyne has sp hybridization with 50% s character.
• This high percentage of s character provides acidic strength to alkynes. Moreover, only terminal alkynes are acidic in nature. Example of alkyne with acidic character is 1-pentyne.

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