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Hydrocarbons

Long Answer Type

181.

Give two reactions of electrophilic addition on acetylene along with their mechanism.

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182. Give two reactions of electrophilic addition on acetylene along with their mechanism.

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183.

How do alkynes react with hypochlorous acids? Discuss its mechanism.
Or
$HC space identical to space CH space rightwards arrow with Cl subscript 2 divided by straight H subscript 2 straight O on top space CHCl subscript 2 space minus space CHO$

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Short Answer Type

184.

How does acetylene react with:
(i) Gaseous chlorine
(ii) Liquid bromine?

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Long Answer Type

185.

Starting from acetylene how will you obtain:
(i) Ethylidene iodide
(ii) Dichloro acetaldehyde
(iii) Ethylene?

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186. 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?

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:

(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.

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