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Abstract-%mass spectra of guanidme and ten of its derivatives have been studied under both high and low resolution conditions. Evidence was detected for themigrationofmethyl groups, the formation of intermediate threemembered ring structures and decompositions involving expulsion of N with release of kinetic energy. INTRODUCTION THERE are no published spectra of guanidine or its derivatives although Loudon, Maccoll and Webb1 have examined the methyl guanidines, measured their ionization potentials, and discussed some of the prominent fragment ions, meta-stable ion transitions and rearrangement mechanisms involved in their fragmentation under electron impact.A detailed study of meta-stable transitions has previously been shown to assist greatly in determining thedissociation processes involved in aromatic nitro compounds8 and cyclic amines., In this present work, therefore, the spectra of guanidine and 10 substituted guanidines were recorded in a double-focusing instrument in such a way that the sensitivity to meta-stable ions was higher than is usually the case. In the mass spectrometer used, the resolving power was adjusted to about 1 part in 800 by using comparatively wide source and collector slits and the gain of the electron multiplier was increased. The composition of each ion species involved in a meta-stable transition was then determined by examination at a resolving power of 1 in 10, OOO and by accurate mass measurement using the peak matching technique.The large numbers of meta-stable transitions detected in this investigation have shown that the fragmentation processes involved proceed along many competing paths. When there is no meta-stable transition linking a prominent fragment ion with any ion of higher mass it is assumed that this ion is produced by very fast processes occurring before the field free region preceding the magnetic analyser, and probably in the ionisation chamber itself.

The n-alkanes, propane to heptane, have been studied in a modified MS-9 mass spectrometer under conditions that enabled the daughter ions, resulting from metastable fragmentation processes occurring in the first field free region, to be observed with high sensitivity. The precursor ions in these fragmentations have been identified unambiguously and a general fragmentation scheme for the n-alkanes is proposed. The mass spectrometer incorporated a variable width monitor slit and narrow settings of this slit improved the energy resolution so that fine structure could be observed in some of the 'metastable peaks'. The implications of this fine structure are discussed. 1009* J. A. Hopkinson, unpublished work.

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