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Hydrocarbons

Long Answer Type

241. How will you convert benzene into:
(i) p-Nitrobromobenzene
(ii) m-Nitrochlorobenzene
(iii) p-Nitrotoluene
(iv) Acetophenone?

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Short Answer Type

242.

Out of benzene, m-dinitrobenzene and toluene which will undergo nitration most easily and why?

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243.

How will you explain the directive influence of alkyl group (in the case of toluene)?

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244.

How will you explain the directive influence of –NH₂ group (in the case of aniline)?

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245.

How will you explain the directive influence of -CHO group?

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246.

How will you explain the directive influence of halogens?

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247.

Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile E⁺:

(a) Chlorobenzene; 2, 4-dinitrochlorobenzene, p- nitro chlorobenzene

(b) Toluene, p-H₃C – C₆H₄ – NO₂, p-O₂N – C₆H₄ – NO₂

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Long Answer Type

248.
What are polynuclear hydrocarbons? Discuss the toxicity of polynuclear hydrocarbons.

Polynuclear hydrocarbons are the compounds which contain two or more benzene rings. They may be either fused or isolated.

(i) Fused polynuclear hydrocarbons: These are condensed aromatic hydrocarbons which contain more than one ring and have two carbons shared by two or more aromatic rings.

(ii) Isolated polynuclear hydrocarbons. In isolated polynuclear hydrocarbons, one or more benzene rings are linked to each other through one or more carbon atoms.

Toxicity of polynuclear hydrocarbons:
There are certain polynuclear hydrocarbons which are cancer producing (i.e. carcinogenic nature). Actually, these are the products of incomplete combustion of organic material such as coal, petroleum, tobacco etc. and become a major cause of human cancer. The following polynuclear hydrocarbons are cancer producing:

It is believed that when these polynuclear hydrocarbons enter the body of a human being, they are first converted into their oxides called epoxides and then into dihydroxy epoxides. The dihydroxy epoxides thus produced react with purine bases (such as guanine) present in DNA and RNA of the human cell, thereby causes mutation and ultimately leads to cancer. Also all over the world, steps are being taken to check the release of such toxic polynuclear hydrocarbons in the atmosphere.

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