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The Molecular Ion of 5‐Methylene‐1,3‐cyclohexadiene: Electronic Absorption Spectrum and Revised Enthalpy of Formation
Author(s) -
Bally Thomas,
Hasselmann Dieter,
Loosen Klaus
Publication year - 1985
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.19850680209
Subject(s) - chemistry , methylene , ion , photoionization , absorption spectroscopy , standard enthalpy of formation , photochemistry , toluene , pyrolysis , absorption (acoustics) , enthalpy , medicinal chemistry , organic chemistry , ionization , physics , quantum mechanics , acoustics
The title compound ( 1 ) is prepared in situ from 5‐methylenebicyclo[2.2.0]hex‐2‐ene by pyrolysis and subsequent photoionization in a photoelectron spectrometer or by X‐ray irradiation in an Ar matrix where its electronic absorption spectrum is obtained. The results confirm earlier conjectures that the title cation exists as a distinct entity on the C 7 H 8 + hypersurface and can be obtained photochemically from other isomeric ions or by a McLafferty rearrangement. The enthalpies of formation of 1 , its precursor and the corresponding radical ions are compared to the most recent data available for other C 7 H 8 isomers and their ions. It is shown that the thermodynamic stability of 1 + is closer to that of toluene cation than concluded on the basis of earlier results.

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