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Hydrocarbons

Short Answer Type

231. What happens when:
Toluene is heated with concentrated sulphuric acid.

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232. What happens when:
p-xylene is heated with alkaline KMnO₄.

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233.

What happens when:
Benzene is treated with n-propyl chloride in the presence of anhydrous AlCl₃.

532 Views

Long Answer Type

234.

Discuss the mechanism of electrophilic substitution reactions of benzene?

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235. Discuss the mechanism of chlorination of benzene.

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236.

How is benzene converted to nitrobenzene? Give mechanism.

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237.
How benzene is converted into benzene sulphonic acid? Give its mechanism.
Or
Explain the mechanism of sulphonation of benzene.

Sulphonation of benzene is carried out by the action of benzene with fuming sulphuric acid or oleum.

Mechanism: It involves the following steps:

(i) Generation of sulphur trioxide (electrophile). The attacking electrophile sulphur trioxide, SO₃ (neutral but electron deficient) is present as such in oleum (H₂SO₄ + SO₃) or can be formed by the dissociation of the sulphuric acid.

The sulphur atom in sulphur trioxide has the only sextet of electrons. Thus the molecule is electron deficient in nature.

(ii) Formation of the carbocation. The electrophile (SO₃) attacks the benzene ring to form intermediate carbocation which is resonance stabilised. It is a slow step.

The resonance hybrid structure of the above resonating form can be represented as

(iii) Transfer of proton from the carbocation to form benzene sulphonate ion.

(iv) The reaction between benzene sulphonate ion and hydronium ion to form benzene sulphonic acid.

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238.

Discuss the mechanism of Friedel Craft’s reaction.
Or
Discuss the mechanism of Friedel Craft’s alkylation of benzene. Give the mechanism of reaction of benzene within the presence of AlCl_3.Or

How is benzene converted into aceto-phenone? Name the reaction and discuss the mechanism explaining each step.

Or

Give the mechanism of acylation of benzene.