Modulating the thermal isomerization barriers of quadricyclane to norbornadiene through cross-conjugative patterns

Computations show that thermal isomerizations of quadricyclane to norbornadiene can be modulated by heteroarene substitution. Heteroarenes that are non-cross-conjugated to the norbornadiene double bond increase delocalization of the transition state structure and lower the thermal activation enthalpy (Δ<i>H</i>^‡), while cross-conjugated analogs increase Δ<i>H</i>^‡ without significantly impacting the storage enthalpy (Δ<i>H</i>_storage).