The mass spectra of mono-and dimethylbicyclo[3,3,l]nonanes have been studied. In addition to the fragmentation of the bicyclic form of the molecular ion, the latter appears to dissociate from its monocyclic form. Structural isomers and stereoisomers with essential differences in thennodynamic stability may be identified by the quantitative differences in their mass spectra. Stereoisomers with a 'boat' conformation of one of the cyclohexane rings have been showu to differ from the stereoisomers with a 'chair' conformation of both rings by virtue of higher intensity of odd-electron ions for the former.Continuing our studies of the application of mass spectrometry to structural and stereochemical problems in the chemistry of saturated cyclic hydrocarbons,' we have investigated the mass spectra of monoand dimethylbicyclo[3.3. llnonanes. The stereochemistry and equilibrium correlations of these hydrocarbons have been studied p r e v i o~s l y .~~~ 1: R, = R, = R, = R,= R, = R 6 = H 2: R,= CH,; R, = R, = R, = R, = R 6 = H 3: R, = CH,; R, = R, = R, = R , = R , = H 4 R, = CH,; R, = R, = R, = Rs = R,=H 5: R, = CH,; R, = R, = R, = R, = R,= H 6: R, = R, = CH,; R, = R, = R,= R,=H 7: R, = R, = CH,; R, = R, = R, = R, = H 9 ' i.;.; R, 3
