ISSN:
0009-2940
Keywords:
C—C Bond cleavage, kinetics of
;
Heats of formation
;
Radicals, stability of
;
Capto-dative effect
;
Geminal substituents, energetic interaction of
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Substituent Effects on the Strength of C—C Bonds, 14[1]. - Kinetic and Thermodynamic Stability of 2,3-Bis(dialkylamino)-1,4-diketones - Energy of Stabilization of α-Dialkylamino α-Carbonylalkyl Radicals with Capto-dative SubstituentsProf. Dr. H.-G. Viehe zum 65. Geburtstag gewidmet.The equilibrium constants and rate constants for the dissociation of the 2,3-bis(dialkylamino)-1,4-diketone diastereomers meso- and DL-7a and 7b were measured over a temperature range of 40°C. From the enthalpies of dissociation ΔHDiss and enthalpies of activation ΔH≠ and the strain enthalpies of 7 the bond dissociation enthalpies BDE(C—C) of 7 were determined. By comparison with the dissociation enthalpies of Ct-Ct alkanes[21] the change of these BDEs(C—C) by the cap-to-dative substitution was determined to be 85.4 kJ mol-1 (20.4 kcal mol-1). The heats of formation ΔHof (g) of a series of amino ketones 8 were determined from their heats of combustion and their heats of evaporation. From the ΔHof(g) values in combination with MM2 calculations of their strain enthalpies strain-free increments CHn[N, CO, C2 - n] with n With n = 0, 1, 2 were derived and geminal interaction enthalpies in the ground states were obtained thereof. The radical stabilization enthalpy RSE of 6 was deduced from the ΔBDE(C—C) values and the ground state effect to be 73.6 kJ mol-1 (17.6 kcal mol-1). From these data and the radical stabilization enthalpies RSE of α-aminoalkyl radicals (4.2 kJ mol-1) and α-carbonyl radicals (28.9 kJ mol-1) a synergetic radical stabilization enthalpy of 40.5 kJ mol-1 (9.7 kcal mol-1) is deduced. This number combines “extra” resonance stabilization and general inductive or anomeric geminal substituent interaction in the radicals. The crystal structure of meso-7a has been determined by X-ray diffraction methods.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19941270420
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