Abstract
Numerous experimental data for the cyclization of free radicals C·H2(CH2)nCH=CH2 → cyclo-[(CH2)n+1CH(C·H2)], and C·H2(CH2)nCH=CHR → cyclo-[(CH2)n+1C·HCHR] were analyzed in the framework of the parabolic model. The activation energy of thermoneutral (ΔHe = 0) cyclization Ee0 decreases linearly with an increase in the energy of cycle strain Ersc: Ee0(n) (kJ mol–1) = 85.5 – 0.44Ersc(n) (n is the number of atoms in the cycle). The activation entropy of cyclization ΔS# also depends on the cycle size: the larger the cycle, the lower ΔS#. A linear dependence of ΔS# on the difference between the entropies of formation S° of cyclic hydrocarbon and the corresponding paraffin was found: ΔS# = 1.00[S°(cycle) – S°(CnH2n+2)]. The Ee0 values coincide for cyclization reactions with the formation of the six-membered cycle and the bimolecular addition of alkyl radicals to olefins.
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