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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?

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187. How does acetylene react with:
(i) Water in the presence of dilute H₂SO₄and HgSO₄(ii) HCN in the presence of barium cyanide?

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188. Explain the catalytic hydrogenation of alkynes.

Catalytic hydrogenation of alkynes: It involves two types of hydrogenation.

(i) Complete hydrogenation: When vapours of alkynes are passed over the surface of the catalyst like Ni, Pt or Pd at 473 K, hydrogenation takes place to form alkenes and then alkanes. For example,

(ii) Controlled hydrogenation. When vapours of alkynes are passed over the heated Lindlar’s catalyst (Pd/CaCO₃) partially poisoned by lead acetate or nickel boride catalyst known as P-2), controlled hydrogenation takes place only up to alkene stage.