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.