Ring-opening of the cyclopropyl radical in the condensed phase: A combined density functional theory/molecular mechanics quasiclassical trajectory study

A combined density functional theory/molecular mechanics quasiclassical trajectory study has been performed to investigate the ring-opening stereochemistry and dynamics of the cyclopropyl radical in both argon and helium condensed phase environments. In a previous theoretical study it was found that the ring-opening of an isolated cyclopropyl radical can occur through both disrotatory and conrotatory pathways. In addition, it was discovered that subsequent rotations of the methylene groups can take place following formation of the allyl radical, altering the reaction stereochemistry. Only at high densities does the environment significantly affect the initial reaction stereochemistry, but does reduce the number of internal rotations in the allyl radical, regardless of solvent density. Analysis of the internal energy and center of mass motion of the solute radical indicate more extensive collisional deactivation in the lower mass He bath, resulting in approximately a 10% increase in the number of disrotatory reactions. This study suggests that the initial stereochemistry of the ring-opening of the cyclopropyl radical is unaffected by collisions with the surrounding gas environment at low inert gas densities.