Identification of n-hepta- and n-octadienes by high-resolution gas chromatography using structure-retention correlations and mass spectrometry

Concentrated dehydrogenation product mixtures of n-heptane and n-octane were separated on squalane capillary columns. All n-heptadienes and n-octadienes were identified, with the exception of those with cumulated double bonds. Because of a lack of standards, retention data and mass spectra, the problem of identification was solved by using structure-retention correlations derived from available retention data for alkenes. The identification was then confirmed by using the ageing effect of a squalane column, which gives rise to characteristic changes in selectivity for different classes of unsaturated hydrocarbons. Confirmation was also made by determination of dI/dT values and by gas chromatography-mass spectrometry. The anomalous behaviour of compounds containing C=C---C---C---C structural elements, as noted before for alkenes, alkynes and alkylbenzenes, was found to occur also with n-alkadienes