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Study of the thermochemistry of the C/sub 2/H/sub 5/ + O/sub 2/ in equilibrium C/sub 2/H/sub 5/O/sub 2/ and t-C/sub 4/H/sub 9/ + O/sub 2/ in equilibrium t-C/sub 4/H/sub 9/O/sub 2/ reactions and of the trend in the alkylperoxy bond strengths

Conference · · J. Phys. Chem.; (United States)
OSTI ID:5698527
; ;

The gas-phase equilibria involving the reactions of ethyl and tert-butyl radicals with molecular oxygen to form the corresponding alkylperoxy radicals have been studied over limited temperature ranges: 336-381/sup 0/C for the C/sub 2/H/sub 5/ + O/sub 2/ system and 277-307/sup 0/C for the t-C/sub 4/H/sub 9/ + O/sub 2/ reaction. The radicals were generated homogeneously in a tubular reactor by the pulsed 248-nm photolysis of C/sub 2/H/sub 5/Br (C/sub 2/H/sub 5/) or the 193-nm photolysis of 4,4-dimethyl-1-pentene (t-C/sub 4/H/sub 9/). The relaxation of the alkyl radical to equilibrium in the presence of O/sub 2/ was monitored in real-time experiments using photoionization mass spectrometry. The experiments yielded at least one value of the equilibrium constant at each temperature studied. The enthalpy changes for both R + O/sub 2/ in equilibrium RO/sub 2/ equilibria were obtained by using a third law procedure combining the measured equilibrium constants with calculated or estimated entropy changes for the same reactions. The thermochemical information obtained on these equilibria, combined with that determined earlier for R = CH/sub 3/ and i-C/sub 3/H/sub 7/, indicates that the R-O/sub 2/ bond strength (-..delta.. H/sub 298//sup 0/) increases from 32 to 37 kcal mol/sup -1/ as the size of the alkyl group increases from CH/sub 3/ to t-C/sub 4/H/sub 9/. 41 references, 2 figures, 3 tables.

Research Organization:
Illinois Institute of Technology, Chicago
OSTI ID:
5698527
Journal Information:
J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 90:3; ISSN JPCHA
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKYL RADICALS
BINDING ENERGY
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
ELEMENTS
ENERGY
ENTHALPY
ETHYL RADICALS
EXPERIMENTAL DATA
FORMATION HEAT
FREE ENTHALPY
HIGH TEMPERATURE
INFORMATION
KINETICS
MEETINGS
NONMETALS
NUMERICAL DATA
OXYGEN
PEROXY RADICALS
PHYSICAL PROPERTIES
RADICALS
REACTION HEAT
REACTION KINETICS
THERMODYNAMIC PROPERTIES