Very low-pressure pyrolysis (VLPP) of penta-1,3-dienes. Kinetics of the unimolecular 1,4-hydrogen elimination from cis-penta-1,3-diene

The thermal unimolecular reactions of cis- and trans-penta-1,3-diene (c-PTD and t-PTD) have been studied over the temperature range of 1002–1235 K using the technique of very low-pressure pyrolysis (VLPP). c-PTD decomposes via 1,4-hydrogen elimination analogous to that previously reported for cis-but-2-ene. RRKM calculations incorporating a six-center transition state show that the experimental rate constants are consistent with the following high-pressure rate expression at 1100 K: where θ = 2.303RT kcal/mol, and the A factor was assumed to be the same as that for cis-but-2-ene. The activation energy is in excellent agreement with that obtained for cis-but-2-ene. t-PTD also undergoes decomposition by H₂ elimination presumably via the prior rapid isomerization to c-PTD the results are in exact agreement with those for c-PTD.