13.22. Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile, E⁺.
(a) Chlorobenzene, 2, 4-dinitrochlorobenzene, p-nitrochlorobenzene
(b) Toluene,p—H₃C—C₆H₄—NO₂, p—O₂N—C₆H₄—NO₂.

<p><strong> (a)</strong> The typical reactions of benzene are electrophilic substitution reactions. Higher the electron-density in the benzene ring, more reactive is the compound towards thesereactions. Since NO₂ is a more powerful electron-withdrawing group than Cl, therefore, more the number of nitro groups, less reactive is the compound. Thus, the overall reactivity decreases in the order:Chlorobenzene &gt; p-nitrochlorobenzene &gt; 2, 4-dinitrochlorobenzene</p><p><strong> (b)</strong> Here, CH₃ group is electron donating but NO₂ group is electron-withdrawing. Therefore, the maximum electron-density will be in toluene, followed by p-nitrotoluene followed by p-dinitrobenzene. Thus, the overall reactivity decreases in the order:Toluene &gt;p—H₃C—C₆H₄—NO₂&gt;p—O₂N—C₆H₄—NO₂.</p>

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