RADICAL STABILIZATION ENTHALPIES OF ALPHA ,ALPHA-BIS(METHOXYCARBONYL)ALKYL AND TRIS(METHOXYCARBONYL)METHYL RADICALS

Heats of formation Delta H-f(0)(g) were determined from enthalpies of combustion Delta H-f(0)(c) and enthalpies of vaporization Delta H-vap( 0) vap or enthalpies of sublimation Delta H-sub(0) for the eight subst ituted methanetricarboxylates 2a-h. From these data and from previousl y determined enthalpies of formation Delta H-f(0) of substituted malon ic esters new thermochemical group increments were derived. From these increments and from the recently published improved increments for ca rboxylic acid esters the gem. interaction enthalpies of two and three COOR groups were calculated. The radical stabilization enthalpies RSE of alpha,alpha-bis(methoxycarbonyl)alkyl (18.2 kJ mol(-1), 1a) and tri s(methoxycarbonyl)methyl radicals (5.2 kJ mol(-1), 1b) were derived fr om kinetic data obtained by means of our previously developed protocol . They were corrected for the gem. interaction energies of the ester g roups in the ground state and are satisfactorily explained by an addit ive stabilizing effect of the ester substituents and by dipolar substi tuent interactions in the radicals. The dipolar energies were taken fr om MM2 calculations.