Bildungsenthalpie und Stabilisierungsenergie des Pentamethylcyclopentadienyl-Radikals

✍ Scribed by Roth, Wolfgang R. ;Hunold, Frank

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 336 KB
• Volume: 1995
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1995199506151

✦ Synopsis

Heat of Formation and Stabilization Energy of the Pentamethylcyclopentadienyl Radical

From the thermolysis of 1 in the presence of 1–60 bar oxygen between 70 and 100°C the activation energy for its dissociation is found to be 27.9 kcal · mol^−1^. Combining this result with the enthalpy of formation of 4 and a forcefield value for 1 leads to DH° (Me~5~C~5~‐H) = 74.1 kcal · mol^−1^ and ΔH (2) = 16.1 kcal · mol^−1^, which differs by 5.4 kcal · mol^−1^ from a value published recently by Walton^[1]^. The low dissociation enthalpy of 1 is caused only by the relieve of 28 kcal · mol^−1^ of strain. With an intrinsic radical stabilization energy (IRSE) of 17.3 kcal · mol^−1^ for 2 there is no justification for an extra stabilization due to cyclic conjugation.