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 = 2.303 RT 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 H 2 elimination presumably via the prior rapid isomerization to c ‐PTD the results are in exact agreement with those for c ‐PTD.