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Hydrocarbons

Short Answer Type

141.

What happens when:

(i) Ethyl alcohol is heated in the presence of Al₂O₃ at 493 K?

(ii) Ethylene dibromide is heated with zinc dust?

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Long Answer Type

142.

Explain the mechanism of the following reaction:

$straight C subscript 2 straight H subscript 5 OH space rightwards arrow from 440 space straight K to Conc. space straight H subscript 2 SO subscript 4 of space CH subscript 2 space equals space CH subscript 2 space plus space straight H subscript 2 straight O$

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143.

How are alkenes prepared from Alkynes ?

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Short Answer Type

144.

The $straight pi$ -bond is weaker than carbon-carbon σ bond. Explain.

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145.

Why are alkenes more reactive than alkanes ?

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Long Answer Type

146.
Why do alkenes undergo electrophilic addition reactions?

Alkenes undergo electrophilic addition reaction. The electrons constituting the bond in the double bond are more mobile, easily detachable and more easily available for the chemical reaction. This means >C = C< can act as a source of electrons. There are certain reagents (electrophiles) which are capable of adding to alkene molecules forming an addition compound. Since such reactions are initiated by the electrophiles, hence are known as Electrophilic addition reactions.

The mechanism proceeds in two steps:
(i) Electromeric effect and electrophilic attack.

(ii) Attack of nucleophile. The nucleophile released in slow step combines with carbocation to give the addition product.