Question

Arrange the following compounds in a decreasing order of the rates of electrophilic addition reaction.

• A. $Q>P>S>R$
• B. $S>Q>R>P$
• C. $P>Q>R>S$
• D. $R>Q>S>P$

Answer 1

The correct option is B $S>Q>R>P$

The addition of an electrophile to the double bond generates a benzylic carbocation. So, the stability of the carbocation governs the rate of the reaction. The more electron donating species at the para position stabilises the carbocation.
Hence the order be: $S>Q>R>P$