2025 H2 Chem P1 Q20 — Arene Solution

The answer is A (\(\text{CH}_3\text{CHCl}_2\) with \(\text{AlCl}_3\)).
G is \(\text{CH}_3\text{CH(C}_6\text{H}_5)_2\): two benzene rings attached to the same carbon, which also carries a \(\text{CH}_3\) group. It is made by Friedel-Crafts alkylation (electrophilic substitution), in which each C-Cl bond of the reagent is replaced by a bond to a benzene ring:
\(2\text{C}_6\text{H}_6 + \text{CH}_3\text{CHCl}_2 \rightarrow \text{CH}_3\text{CH(C}_6\text{H}_5)_2 + 2\text{HCl}\)
• The reagent must be \(\text{CH}_3\text{CHCl}_2\), with both Cl atoms on the same carbon, so both rings end up on that one carbon.
• The catalyst must be the Lewis acid \(\text{AlCl}_3\), which polarises the C-Cl bond to generate the electrophile.
• B is wrong: \(\text{PCl}_3\) is not a Friedel-Crafts catalyst.
• C is wrong: in \(\text{CH}_3\text{CH(CH}_2\text{Cl)}_2\) the two Cl atoms are on different carbons, so the product would be \(\text{CH}_3\text{CH(CH}_2\text{C}_6\text{H}_5)_2\), with the rings on two different carbons, not G.
• D is wrong: wrong reagent (as in C) and wrong catalyst (as in B).