Rotational barriers in pentadienyl and pent-2-en-4-ynyl radicals

Abstract

The barrier to internal rotation about the C(2)–C(3) bond in pentadienyl radicals was measured by line-shape analysis of the e.s.r. spectrum in the temperature range 320–420 K. The energy difference between the trans- and cis-conformers of pent-2-en-4-ynyl radicals was obtained from the temperature variation of their equilibrium concentration ratio and the barrier to interconversion was determined by e.s.r. line-shape analysis in the range 375–450 K. The rotational barriers and the corresponding stabilisation energies were in good agreement with previous estimates.