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Thermal Rearrangements, XX^[1]^ The Kinetics of Thermal Isomerisation of 4‐Methyl‐1,2,5‐hexatriene in the Gas Phase by Henning Hopf; Gerhard Wachholz; Robin Walsh is a Chemistry article available to read on EtoBox.

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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.

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Author

Henning Hopf; Gerhard Wachholz; Robin Walsh

Publisher

Wiley (John Wiley & Sons); John Wiley & Sons Ltd.; Wiley (ISSN 0009-2940)

Published

1992

Language

EN

Field

Chemistry (Physical Sciences)