ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The thermal unimolecular decomposition of hex-1-ene-3-yne (HEY) has been investigated over the temperature range 949-1230 K using the technique of very low-pressure pyrolysis (VLPP). One reaction pathway is the expected C5—C6 bond fission to form the resonance-stabilized 3-ethenylpropargyl radical. There is a concurrent process producing molecular hydrogen which probably occurs via the intermediate formation of hexatrienes and cyclohexa-1,3-diene. RRKM calculations yield the extrapolated high-pressure rate parameters at 1100 K given by the expressions 1016.0±0.3 exp(-300.4 ± 12.6 kJ mol-1/RT) s-1 for bond fission and 1013.2+0.4 exp(-247.7 ± 8.4 kJ mol-1/RT) for the overall formation of hydrogen. The A factors were assigned from the results of previous studies of related alkynes, alkenes, and alkadienes. The activation energy for the bond fission reaction leads to ΔHf300° [H2CCHCCĊH2] = 391.9, DH300° [H2CCHCCCH2—H] = 363.3, and a resonance stabilization energy of 56.9 ± 14.0 kJ mol-1 for the 3-ethenylpropargyl radical, based on a value of 420.2 kJ mol-1 for the primary C—H bond dissociation energy in alkanes. Comparison with the revised value of 46.6 kJ mol-1 for the resonance energy of the unsubstituted propargyl radical indicates that the ethenyl substituent (CH2=CH) on the terminal carbon atom has only a small effect on the propargyl resonance energy. © John Wiley & Sons, Inc.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550240903
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