ISSN:
0009-2940
Keywords:
Heats of formation
;
Bond cleavage
;
C—C
;
kinetics of
;
Radicals
;
stability of
;
Correlation between heats of vaporization and solvent-accessible surfaces
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
From thermochemical measurements the heats of formation ΔH0f(g) forfluorene (1), 9-methylfluorene (2), 9,9′-bifluorenyl (5), and 9,9′-dimethyl-9,9′-bifluorenyl (6) were determined. The homolytic cleavage of the dimers 5 and 6 to 9-fluorenyl (3) and 9-methyl-9-fluorenyl radicals (4), respectively, was studied in mesitylene with thiophenol as trapping agent and found to follow first-order kinetics. The activation parameters ΔH≠(5) = 212.6 (±2.1) kJ mol-1, ΔS≠(5) = 70.3 (±4.2) J mol-1 K-1 ΔH≠(6) = 164.9 (±0.7) kJ mol-1, and ΔS≠(6) = 88.2 (±1.9) J mol-1 K-1 were obtained. For 3 and 4 the radical stabilization energies RSE(3) = 67 (±7) kJ mol-1 (relative to isopropyl) and RSE(4) = 64 (±8) kJ mol-1 (relative to tert-butyl) were determined by a comparison with the activation parameters of the thermolysis of alkanes possessing the same strain enthalpy. The heats of formation for 3 and 4 and the C-H bond dissociation energies for the C-H bond in the 9-position of 1 and 2 were determined to be ΔH0f(g,3) = 300 kJ mol-1, Δ0f(g,4) = 268 kJ mol-1, BDEC—H(1) = 343 and BDEC—H(2) = 338 kJ mol-1 (estimated errors correspond to those of the RSE values). A good correlation between the heats of vaporization of 37 aromatic hydrocarbons and their calculated solvent-accessible surfaces was demonstrated. Hence, a new method to estimate heats of vaporization was established.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19941270619
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