ISSN:
0009-2940
Keywords:
1,2,5-Hexatriene, 4-methyl-, thermal isomerisation
;
Kinetic measurements
;
Thermal isomerisations
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
4-Methyl-1,2,5-hexatriene (13) has been prepared and subjected to gas-phase pyrolysis. Above 220°C, 13 rearranges reversibly to both trans-5-hepten-1-yne (14) and its cis-isomer 15. Formation of 14 is faster than that of 15. These isomerisations are accompanied by a slower irreversible rearrangement to 1-methyl-4-methylene-1-cyclopentene (16) and 1-methyl-3-methylene-1-cyclopentene (17). Rate constants and Arrhenius parameters have been obtained for all these reactions which were shown to be homogeneous and unimolecular. For the processes 13 ⇄ 14 and 13 ⇄ 15 the data are consistent with [3,3] Cope-type sigmatropic rearrangements. For the process 13 → 16 + 17, a rate-determining formation of the 1-methyl-3-methylenecyclopentane-2,5-diyl diradical is proposed. The rearrangements form a consistent pattern with other known examples. - The equilibrium data are shown to be in good agreement with thermodynamic estimates based on Group Additivity. The additivity scheme of Benson required extension to provide values for two new group contributions.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19921250326
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