Premium
Kinetics of the thermal unimolecular decomposition of hex‐1‐ene‐3‐yne. Heat of formation and resonance stabilization energy of the 3‐ethenylpropargyl radical
Author(s) -
Staker Warren S.,
King Keith D.,
Nguyen Tam T.
Publication year - 1992
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550240903
Subject(s) - chemistry , propargyl , activation energy , bond dissociation energy , resonance (particle physics) , intramolecular force , thermal decomposition , fission , radical , isomerization , kinetic energy , bond cleavage , dissociation (chemistry) , computational chemistry , photochemistry , stereochemistry , organic chemistry , catalysis , physics , quantum mechanics , neutron , particle physics
Abstract 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 C 5 C 6 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 10 16.0±0.3 exp(−300.4 ± 12.6 kJ mol −1 / RT ) s −1 for bond fission and 10 13.2+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 Δ H f 300 °[H 2 CCHCCĊH 2 ] = 391.9, DH 300 °[H 2 CCHCCCH 2 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 CH 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 (CH 2 CH) on the terminal carbon atom has only a small effect on the propargyl resonance energy. © John Wiley & Sons, Inc.