Page 121 - Pharm.Org.Chem-I 02-06-05-101

Acidity of alkynes

Any hydrogen attached to a triple-bonded carbon can be
removed by a very strong base, e.g. NaNH2 (Na in liq.
NH3.

Note: NaOH or alkoxides cannot remove the
acetylenic proton.
Order of decreasing acidity:
Alkynes> Alkenes > Alkanes
Find out the reason? Hint: S-character %

Due to acidity of acetylene hydrogen

• Terminal alkynes can be differentiated from internal
alkynes by reaction with silver ammonium
hydroxide to produce a silver alkynide precipitate.

• Because an internal alkyne has no acidic hydrogen,
it does not react with silver ammonium hydroxide

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