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please explain me about '' acidity of alkynes'' with some examples...

please explain me about  ''acidity of alkynes''   with some examples...



Grade:11

1 Answers

SAGAR SINGH - IIT DELHI
879 Points
10 years ago

Dear student,

ACIDITY OF ALKYNES

 

 

 

Acetylene and other terminal alkynes (1- alkynes) are weakly acidic in character

 

                                                                                                    

            Ex. CH ≡ CH + NaNH2 ————→ H – C ≡ C Na+ + 1/2 H2 
 
                                                                                     (Monosodium acetylide)
 

 

The acetylenic hydrogen of alkynes can be replaced by copper (I) and silver (I) ions. They react with ammonical solutions of cuprous chloride and silver nitrate to form the corresponding copper and silver alkynides.

 

 

CH ≡ CH + 2[Cu(NH3)2]Cl ———→ Cu – C ≡ C – Cu + 2NH4Cl + 2NH3 Dicopper acetylide (Red ppt)

 

 

CH ≡ CH + 2[Ag(NH3)2]NO3 ———→ AgC ≡ C – Ag + 2NH4NO3 + 2NH3 Disilver acetylide (white ppt)

 

 

This reaction can be used to distinguish between 2-alkynes and 1-alkynes. 1-alkynes will give this test while 2-alkynes, will not give this test.

 

 

 

 

CH3 – C ≡ CH + 2[Ag(NH3)2] NO3 ———→ CH3 – C ≡ C – Ag
      1-propyne

 

CH3 – C ≡ C – CH3 + 2[Ag(NH3)2]NO3 ————→ No reaction

 

 

EXPLANATION FOR THE ACIDIC CHARACTER

 

 

 

 It explained by sp hybridization. We know that an electron in s–orbital is more tightly held than in a p-orbital. In sp hybridization s-character is more (50%) as compared to sp2 (33%) or sp3 (25%), due to large s-character the carbon atom is quite electronegative.

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