Question
Give a brief account of the nucleophilic addition in alkynes.
Or
What is the role of Hg2+ ions in the nucleophilic addition reaction of alkynes?
Solution
Nucleophilic addition reaction of alkynes is generally catalysed by the presence of heavy metal salts such as those of mercury and barium. The function of mercury ions (Hg2+) or barium ions (Ba2+) is to form 7r-complex by withdrawing the electron density from the 
-cloud.
As a result, the electron density in the triple bond gets considerably reduced and therefore, the nucleophilic attack is facilitated.
In other words,
-complex formation is responsible for the nucleophilic addition reaction of alkynes. For example, alkynes undergo following nucleophilic addition reactions:
-cloud.As a result, the electron density in the triple bond gets considerably reduced and therefore, the nucleophilic attack is facilitated.
In other words,
-complex formation is responsible for the nucleophilic addition reaction of alkynes. For example, alkynes undergo following nucleophilic addition reactions:(i) The addition of water in the presence of dilute H2SO4 and HgSO4.
(ii) The addition of HCN in the presence of Ba(CN)2.
(iii) The addition of acetic acid in the presence of Hg2+ ion.
