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Thermische Stabilität von 9,9′‐Bixanthen und 9,9′,10,10′‐Tetrahydro‐ 10,10,10′,10′‐tetramethyl‐9,9′‐bianthracen Stabilisierungsenergie planarer Benzhydryl‐Radikale [2]
Author(s) -
Herberg Clemens,
Beckhaus HansDieter,
Rüchardt Christoph
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19941271032
Subject(s) - chemistry , radical , kinetics , medicinal chemistry , standard enthalpy of formation , enthalpy , stereochemistry , organic chemistry , thermodynamics , physics , quantum mechanics
The thermal cleavage of the central CC bonds in the title compounds was investigated. The activation parameters were obtained from kinetics and the equilibrium enthalpies and entropies from the temperature dependence of the equilibrium radical concentrations, determined by quantitative ESR. Δ H ≠ and Δ H Diss are nearly identical but not ΔS ≠ and Δ S Diss , as expected. The radical stabilisation enthalpies RSE obtained from these data (RSE: 7a = 17.9 ± 1.3; 7b = 15.6 ± 1.4 kcal/mol) correspond closely to twice the RSE of α‐phenylethyl radicals (8.0 ± 1.5 kcal/mol) determined previously. The smaller RSE of the benzhydryl radical (12.9 ± 0.9 kcal/ mol), therefore, must be due to its nonplanarity.