= Solution
Number the ring with <chlorine> at C1 and the methylsulfonyl group at C4. \b[The new <nitro group> is at C2, equivalently C6 by the starting ring's symmetry:] the <product (chemistry)> is 1-chloro-2-nitro-4-(methylsulfonyl)<benzene>. Both <substituents> favour this site. Although <chlorine> deactivates the ring inductively, its <lone pair> donation stabilizes ortho/para <Wheland intermediates>. The <sulfone> is strongly <electron> withdrawing and meta directing; attack ortho or para to it produces especially unfavourable cationic contributors to <resonance in chemistry>. C2 is ortho to <chlorine> and meta to <sulfone>, whereas C3 has the opposite, less favourable relationship.
<sulfuric acid> protonates <nitric acid>, followed by loss of <water> to produce the <nitronium ion>. A ring <pi bond> attacks <nitrogen>, giving the <Wheland intermediate> with the new C–N bond. <deprotonation> at the attacked <carbon> restores <aromaticity>. This is <electrophilic aromatic substitution>: the aryl <chloride> and the <sulfone> both remain attached. The formula check is $\mathrm{C_7H_7ClO_2S+NO_2-H=C_7H_6ClNO_4S}$. It confirms replacement of one ring <hydrogen> rather than <chlorine>, but directing effects, rather than the formula alone, establish the position.
\Image[/past-exam-of-the-chemistry-b-course-of-the-university-of-cambridge/2023/paper-1-aromatic-products.png]
{title=Independently drawn aromatic substitution products and the sites selected by protodebromination}
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