82614-49-1Relevant articles and documents
Substituent Effects on the Strength of C-C Bonds, 13. - Kinetic and Thermodynamic Stability of α-alkylated α-Amino Acid Esters - Energy of Stabilization of α-Amino-α-(ethoxycarbonyl)alkyl Radicals
Schulze, Rainer,Beckhaus, Hans-Dieter,Ruechardt, Christoph
, p. 1031 - 1038 (2007/10/02)
Thermolytic cleavage of 1a-c and 2a-c into radicals in solution are clean first-order processes.The activation parameters for C-C bond homolysis were determined.Compared with the corresponding data for hydrocarbons of equal strain a decrease of bond strength of 14.4 kcal/mol results by the combined interaction of the amino and the ethoxycarbonyl substituents.The heat of formation of 5 was determined by combustion calorimetry c(l) = -1207.75 +/- 0.20 kcal/mol> combined with the heat of vaporization (ΔH0v = 13.31 +/- 0.10 kcal/mol).Compared with the additive behaviour of group increments the resulting heat of formation (ΔH0f(g) = -112.02 +/- 0.24 kcal/mol> suggests a synergetic, geminal destabilization of Hsyn = 1.9 +/- 1.4 kcal/mol.Combination of the kinetic data of bond homolysis of 1a-c and 2a-c with the synergetic ground-state destabilization leads to a synergetic, capto-dative radical stabilization of Hsyn(rad) = 6.7 kcal/mol.Key Words: C-C Bond cleavage, kinetics of / Heat of formation / Radicals, stability of / Capto-dative effect / Geminal substituents, energetic interaction of
