Studies in photochemistry. Part IX. Stilbene analogues which fail to undergo photocyclisation to phenanthrene analogues

Abstract

Stilbene analogues which have low values for the free-valence indices at the atoms between which the new bond would form on cyclisation fail to photocyclise. Similarly, substituents present which promote a high degree of intersystem crossing also prevent photocyclisation. Failure of compounds to cyclise on electron impact is correlated with the failure of such compounds to photocyclise. The photodimerisation of trans-benzylidenephthalide is also discussed.