Why is 1-bromotriptycene inert to nucleophilic substitution? According to my textbook, 1-bromotriptycene is inert to any nucleophilic substitutions.



Due to steric hinderance we can say SN2 reactions cannot occur, but I think SN1 reactions should be favoured as formed carbocation will be resonance stabilised.

Can someone explain why it doesn’t undergo SN1 reactions?
Sn1 reaction proceed through carbocation intermediate which has planar structure. The structure of 1-bromo triptycene  is cage like structure so the bridgehead carbon cannot assume planarity , hence,the formation of a carbocation at the bridgehead position does not take place. Consequently 1-bromotriptycene is inert to sn1reaction.