Breakdown graphs have been constructed from charge exchange data for the ephneric 2-methyl-, 3-methyland 4-methyl-cyclohexanols. Although the breakdown graphs for ephneric p a h are essentialIy identical above -12eV recombination energy, significant M e r e n c a are observed for the epimeric 2-methyl-and 4-methyl-cyclohexanols at low internal energies. For the 2-methylcydohexanols the ratio (W-H,O]'?
M")J([M-H+O]"/M+'),, is 3.2 in the [c.&]+' charge exchange mass spectra. This is attributed to both energetic and conformational effects which favour the stereospecific cis-1,4-H2O elimination for the cis epimer. Tbe breakdown graph for trans-4-methylcyclohexanol shows a sharp peak in the abundance of the ]" ion at -lOeV recombination energy which is absent from the breakdown graph for the cis epimer. This peak is attriiuted to the stereospecific cis-1,4-elimination of water from the molecular ion of the trans isomer; the reaction appears to have a low critical energy but a very unfavourable frequency factor, and alternative modes of water loss common to both epimers are observed at higher energies. As a result, in the [GF61+' charge exchange mass spectra the (F1-H,01"/F11+9~/~F1-H201"/F11+'), ratio is -24, compared to the value of 13 observed in the 70 eV E l mas spectra. No dillereare observed in either the metastable ion abrmdances or the associated kinetic energy releases for epimeric molecules.