This reaction is forbidden. The symmetries of the orbitals are such that one interaction isbonding and the other is antibonding.The same answer is obtained if the HOMO of allyl cation and the LUMO of ethylene areexamined.(b)In this part of the exercise we consider the LUMO of allyl cation and the HOMO of 1,3-butadiene.This reaction is allowed by the Woodward–Hoffmann rules. Both interactions are bonding.The same prediction would be arrived at if the HOMO of allyl cation and LUMO of 1,3-buta-diene were the orbitals considered.10.39Since oxygen has two unpaired electrons, it can abstract a hydrogen atom from the allylic positionof cyclohexene to give a free-radical intermediate.The cyclohexenyl radical is resonance-stabilized. It reacts further via the following two propagation
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