Tris (methylidene)-cyclopropane (“[3]Radialene”) Part 1. Enthalpy of formation and strain energy

✍ Scribed by Thomas Bally; Helmut Baumgärtel; Ulrich Büchler; Edwin Haselbach; Wolfgang Lohr; John P. Maier; Jürgen Vogt

• Publisher: John Wiley and Sons
• Year: 1978
• Tongue: German
• Weight: 713 KB
• Volume: 61
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19780610222

✦ Synopsis

Abstract

The enthalpy of formation of tris(methylidene)‐cyclopropane (“[3]radialene”, 1) has been determined as Δ__H__ = 396 ± 12 kJ mol^−1^ from three fragmentation reactions of its molecular ion 1^+^ formed from 1 by photoionisation using synchrotron radiation. Comparative electron impact measurements using conventional mass spectrometry were also performed. A treatment of the latter data is described which leads to satisfactory agreement with the photoionization data. The experimental value of Δ__H__(1) is compared with various theoretical estimates. The strain energy of 1 is calculated to be 226.3 kJ mol^−1^. Linear extrapolation of this quantity from the increase of strain in passing from cyclopropane to methylidenecyclopropane yields 282.4 kJ mol^−1^. The discrepancy between these values, already predicted by Dewar and Baird ten years ago from theoretical calculations, is discussed on the basis of maximum overlap considerations. The enthalpy of formation of bis(methylidene)cyclopropane is predicted to be ΔH= 309 kJ mol^−1^.