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Four aryl chlorides, (I) chlorobenzene, (II) 1-chloro-4-nitrobenzene, (III) 1-chloro-2,4-dinitrobenzene and (IV) 2-chloro-1,3,5-trinitrobenzene, are treated with sodium methoxide in methanol. The correct order of decreasing rate is

  1. AIV III II I
  2. BI II III IV
  3. CIII IV II I
  4. DIV II III I

Answer: A

The rate of SNAr increases with the number of nitro groups at ortho and para positions. These are 0, 1 (para), 2 (ortho, para) and 3 (two ortho, one para) for I, II, III and IV. Each extra activating group stabilises the Meisenheimer complex more. The order is IV III II I.
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