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🧪 Chemistry  ·  Hydrocarbons  ·  NEET & JEE

Why are terminal alkynes acidic?

Answer: sp hybridised carbon has high s-character.

  • A The pi bond delocalises the negative charge onto the adjacent carbon
  • B sp hybridised carbon has high s-character
  • C Resonance stabilises the resulting carbanion across the triple bond
  • D The electron-withdrawing inductive effect of the second carbon

Correct answer: B. sp hybridised carbon has high s-character

Explanation: sp hybridised carbon holds electrons more tightly due to high s-character, making the C-H bond more polar and acidic.

Hybridisation and Bonding in HydrocarbonsCCEthane: sp³, single bond109.5°, free rotationCCEthene: sp², double bond120°, planar, NO rotationCCEthyne: sp, triple bond180°, linearMore bonds between the same 2 carbons = shorter, stronger, but more reactive bond

Going from a single to a triple bond between carbons increases the s-character of hybridisation (sp³→sp²→sp), shortening the bond and locking the geometry, while increasing π-bond reactivity (alkenes and alkynes readily undergo addition reactions that alkanes don't).

Concept context

The simplest organic compounds made only of carbon and hydrogen. Covers alkanes, alkenes, alkynes, and aromatic compounds like benzene. Learn preparation methods, key reactions, and physical properties.

Read the full Hydrocarbons notes →