Influence of the size of the formed cycle on the reactivity of free radicals in cyclization reactions

Numerous experimental data for the cyclization of free radicals (CH2)-H-circle(CH2)(n)CH=CH2 --> cyclo-[(CH2)(n+1)[CH((CH2)-H-circle)], and (CH2)-H-circle(CH2)(n)CH=CHR--> cyclo-[(CH2)(n+1)(circleHCHR)-H-C] were analyzed in the framework of the parabolic model. The activation energy of thermoneutral (DeltaH(e) = 0) cyclization E-e0 decreases linearly with an increase in the energy of cycle strain E-rsc: E-e0(n)(kJ mol(-1)) = 85.5-0.44E(rsc)(n) (n is the number of atoms in the cycle). The activation entropy of cyclization DeltaS(not equal) also depends on the cycle size: the larger the cycle, the lower DeltaS(not equal). A linear dependence of DeltaS(not equal) on the difference between the entropies of formation Sdegrees of cyclic hydrocarbon and the corresponding paraffin was found: DeltaS(not equal) = 1.00[Sdegrees(cycle)-Sdegrees(CnH2n+2)]. The E-e0 values coincide for cyclization reactions with the formation of the six-membered cycle and the bimolecular addition of alkyl radicals to olefins.