Cyclisation of alkoxy radicals. A semiempirical MNDO-PM3 study

Abstract

The reactivity of the butoxy and 3-methylcyclohexyl radicals, as representatives of alkoxy radicals, was studied by MNDO-PM3 semiempirical MO method. In both cases it was found that the oxy radical underwent easily 1,5-H migration giving a δ-hydroxyalkyl radical. The hydrogen abstraction reaction goes through two transition states. The first transition state (TS) with short O–H distance has an energy very similar to, or lower than, the TS for 1,5-H migration. The second TS is of higher energy and is much product-like. The overall cyclisation reaction has a high activation energy (over 40 kcal mol ^–1), and is therefore unlikely to occur spontaneously. Most likely, the cyclisation step needs assistance of some other surrounding molecules to speed up the reaction.