The barrier to internal rotation about the C(2)-C(3) bond in pentadienyl radicals was measured by lineshape 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 t o 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.
Hydrogen abstraction from 2-halogenoethylamines is followed by dehydrohalogenation to give 1 -aza-ally1 radicals which show significantly greater spin density at the CH2 terminus than do ally1 radicals.1and 2-aza-ally1 radicals are the archetypes for all delocalised radicals containing nitrogen and have consequently been sought experimentally and studied theoretically.1 Several diaza-ally1 radicals (1) have been observed by e.s.r. spectro-scopy2J and some substituted triazenyl radicals (2) were detected recently.4>5 Neither the 1-aza-ally1 (3) nor the 2-aza-ally1 radicals (4) had been observed prior to the present work, although some cyclic and acyclic derivatives of the latter were examined by e.s.r. spectroscopy6~7 and three 4,4dimethyloxazolinylmethyl radicals (5) have been reported?Hydrogen abstraction from primary amines by photochemically generated !-butoxy radicals gives mainly 1aminoalkyl radicals, RCHNH2,G10 which can be observed over a wide temperature range by e.s.r. spectroscopy.ll Some abstraction of the amino hydrogens may occur to give aminyl radicals12J3 but alkylaminyls are not in general detectable by e.s.r. in solution.12.14The photochemical reaction of 2-fluoroethylamine with di-t-butylperoxide in hydrocarbon solvents gave the e .s.r .spectrum shown in Figure 1.t Two radicals were observable in the range 160 to 290 K, their concentration ratio being 2.5 : 1 at 262 K. The same two radicals were detected when 2-
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