Question

b Rank by arenium ion stability. The arenium ion that is the lowest in energy (most stable) is I, while the arenium ion that is highest in energy is 5. HN NH HN Br Br H Br H Br

Please fully explain how to get the answer and any/every rule to help determine the ranking of arenium ion stability. Thank you!

Answer 1

On basis of M effect and inductive effect and high Electron density at ring of benzene

On basis of M effect and inductive effect and high Electron density at ring of benzene S = Substituent rightarrow In case of Orth's pear attack positive charge reaches at carbon which bonded with external substituent in meta attack positive charge does not reach at carbon which bonded with external substituent during the Resonance implies Arenium Ion possess positive charge so it's require e^negativity density for Higher stability. Implies S implies e^negativity donating group (ERG) or EDG Pear attack > ortho attack > Meta attack > Normal Arenium Ion S implies EWG implies e^negativity withdrawing group Normal Arenium > Meta attack > Pear attack > ortho attack Inductive effect proportional to 1/distance I-effect strength implies ortho > Meta > Pear implies Mesmeric effect only present at ortho and Para position not at Meta. + M implies Increase e^negativity density at ortho spear position -M implies Decreases e^negativity density at ortho spear position implies stability of alpha + M alpha + I