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Tris (methylidene)‐cyclopropane (“[3]Radialene”) Part 1. Enthalpy of formation and strain energy
Author(s) -
Bally Thomas,
Baumgärtel Helmut,
Büchler Ulrich,
Haselbach Edwin,
Lohr Wolfgang,
Maier John P.,
Vogt Jürgen
Publication year - 1978
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19780610222
Subject(s) - cyclopropane , chemistry , photoionization , enthalpy , standard enthalpy of formation , bond dissociation energy , fragmentation (computing) , tris , standard enthalpy change of formation , analytical chemistry (journal) , ion , dissociation (chemistry) , thermodynamics , organic chemistry , ionization , ring (chemistry) , physics , computer science , operating system , biochemistry
The enthalpy of formation of tris(methylidene)‐cyclopropane (“[3]radialene”, 1 ) has been determined as Δ H f O= 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 f O ( 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 f O = 309 kJ mol −1 .