Trapping of allylic radicals from the gas phase pyrolysis in the adamantane matrix - Isotropic ESR spectra at 77 K

Abstract

A simple device has been developed and tested for trapping radicals from the gas phase onto a cold finger kept at 77 K. The yields of allylic radicals obtained by pyrolysis of biallyl hydrocarbons were studied by ESR spectroscopy in dependence on the temperature and pressure of pyrolysis, both in the absence and presence of adamantane. The co-deposition of the radicals with adamantane increased considerably the radical yields and afforded isotropic ESR spectra of allyl radicals (ΔHmin = 0.21 mT) even at 77 K. The adamantane matrix formed from the gas phase appeared to be less rigid than the crystalline one, as the allylic radicals decayed already at 160-177 K. Yields of the trapped allyl radicals were also compared with the radical yields measured by mass spectrometry using analogous pyrolytic device.