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Substituent effects on the CC bond strength, 19 . Geminal substituent effects, 10 . Radical stabilization enthalpies of α,α‐bis(methoxycarbonyl)alkyl and tris(methoxycarbonyl)methyl radicals
Author(s) -
Rakufs Klaus,
Verevkin Sergey P.,
Keller Manfred,
Beckhaus HansDieter,
Rüchardt Christoph
Publication year - 1995
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.1995199508203
Subject(s) - chemistry , substituent , geminal , standard enthalpy of formation , radical , medicinal chemistry , isodesmic reaction , sublimation (psychology) , alkyl , enthalpy , computational chemistry , organic chemistry , thermodynamics , psychology , physics , psychotherapist
Heats of formation Δ H f 0 ( g ) were determined from enthalpies of combustion Δ H f 0 (c) and enthalpies of vaporization Δ H vap 0or enthalpies of sublimation Δ H sub 0for the eight substituted methanetricarboxylates 2a ‐ h . From these data and from previously determined enthalpies of formation Δ f 0of substituted malonic esters new thermochemical group increments were derived. From these increments and from the recently published improved increments for carboxylic acid esters the gem. interaction enthalpies of two and three COOR groups were calculated. The radical stabilization enthalpies RSE of α,α‐bis(methoxycarbonyl)alkyl (18.2 kJ mol −1 , 1a ) and tris‐(methoxycarbonyl)methyl radicals (5.2 kJ mol −1 , 1b ) were derived from kinetic data obtained by means of our previously developed protocol. They were corrected for the gem. interaction energies of the ester groups in the ground state and are satisfactorily explained by an additive stabilizing effect of the ester substituents and by dipolar substituent interactions in the radicals. The dipolar energies were taken from MM2 calculations.