Problem -

Find which carbon is most susceptible to electrophilic attack (among carbons numbered $1$ to $6$): enter image description here

Answer given (may not be the correct one) -


My question -

$1.$ I know that $\ce{-CCl3}$ group exerts a negative hyperconjugation effect, hence acting as a deactivating and meta-directing group. If $\ce{-CF3}$ has a similar effect (which dominates over $\mathrm{-I}$ effect), then in that case phenyl ring D will be more electron-rich as compared to ring B - since the ring B, being attached at para of the main ring A, will participate in resonance due to the negative hyperconjugation of $\ce{-CF3}$ group. Since resonance does not result in a positive charge at the meta carbon of ring A, so I feel ring C should be more susceptible to electrophile. Within ring C, I expect only inductive effect to operate, so the carbon farthest from ring A will be richest in electrons. Accordingly my answer in this case will be $5$.

$2.$ If $\ce{-CF3}$ does not exert negative hyperconjugation - then in that case, only inductive effect will decide the electron density and consequently the carbon farthest from $\ce{-CF3}$ group will be most electron-rich. My answer in this case will be $6$.

In either case, I don't see how $2$ can be the answer. Is the answer key wrong? If yes, then which of my two reasonings is correct? If no, then what am I missing?

  • $\begingroup$ @Ashish Ahuja - it does, it's the same question from the same test paper! $\endgroup$
    – TRC
    Jul 22 '21 at 6:34
  • $\begingroup$ If you don't mind, can you tell me whether, the paper mentioned is for mains or adv? $\endgroup$
    – Rishi
    Jul 22 '21 at 9:21
  • $\begingroup$ @Rishi Advanced - and their answer key to this one was wrong btw, the correct answer is 4. $\endgroup$
    – TRC
    Jul 22 '21 at 13:31