The e.s.r. spectrum of the homoallylic radical (C) is observed when a mixture of di-t-butyl peroxide and a cyclopropylcarbinol (A; R = H or alkyl) is photolysed at low temperature, but near room temperature the spectrum shows that the enolic hydrogen has been transferred to the alkyl radical to give the enoxyl radical (D). Studies of the thermolysis of di-t-butyl peroxide or of di-t-butyl hyponitrite in the presence of 1 -cyclopropylethan[~H]ol confirmed that deuterium was located in the &position of the pentan-2-one which was formed. The same sequence 8 e of radicals (B) (0) (R = Me) occurs when cyclopropyl methyl ketone is photolysed in the presence of 1 -cyclopropylethanol. Aryl(cyclopropyl)methanols (A; R = Ar) yield only the radical (B). and no ring opening could be detected. 2-( Hydroxymethy1)oxiran shows the formation of the 3-hydroxyprop-2-enoxyl radical, consistent with the occurrence of ring opening and hydrogen transfer from enolic oxygen to oxygen, but no evidence could be found for transfer of hydrogen from lactim oxygen to carbon, or from enolic oxygen to nitrogen. in the reactions of 1or 2-hydroxyalkylaziridines.
(C)THE ability of phenols to donate their hydroxylic hydrogen to a variety of radicals is well known, and is exploited in , for example , the stabilisation of alkenes against polymerisation , or of hydrocarbons against autoxidation.1 Alcohols, on the other hand, do not usually transfer hydroxylic hydrogen homolytically, although it has recently been shown2*8 that such hydrogen transfer can occur from alcohols to alkoxyl radicals when the alcohols are not hydrogen b0nded.tThis difference in behaviour between phenols and alcohols is attributed to the thermodynamic and kinetic stabilisation of the phenoxyl radical which occurs when the unpaired electron is delocalised over the aromatic ring.No comparable work appears to have been reported on the ability of simple enols to donate hydroxylic hydrogen, doubtless because the enols could not be prepared and handled uncontaminated by the corre-sponding keto-compounds. We have now made use of the ring-opening reactions of cyclopropylhydroxymethyl, (hydroxy) oxiranylmet hyl, and aziridinylhydroxymethyl radicals (I; X = CH,, 0, or NR') to form the pure enols in sitzc, and have established by e.s.r. spectroscopy that, for the first two classes of compound, transfer of the hydroxylic hydrogen to the radical centre X . (X* = CH,. or 0.) does occur, in all probability by a l,6-shift [equation (l)] .s ( 1 ) Similar work on the cyclopropylhydroxylmethyl radicals (I; X* = CH,.) has recently been carried out independently by Itzel and Fischer,g with very similar results and conclusions. t The assumption that hydrogen bonding always reduces the 4 M. Simonyi, J. Kerdos, I. Fitos, I. I(ov&s, a d J. PosP~,~& hydrogen-donating ability of a hydroxy-group has recently been discounted.'
