The mass spectra of some methyl norbornyl chlorides

Abstract

The mass spectra of exo-2-norbornyl chloride, 1-and 2-methyl exo-2-norborny1, exocamphenilyl, apoisobornyl, bornyl and isobornyl chloride, and camphene hydrochloride, a-and bfenchyl chloride and fenchene hydrochloride, and exo-isofenchyl chloride and 2,5,5-trimethyl exo-2-norbornylchloride,andcampheneand a-fenchene have beenexaminedat 12 to 16 and 80 eV and at 30 to 49 and 80", or higher temperatures. Wagner-Meerwein rearrangenients occur very readily in the ion source and compounds reiated by these rearrangenients give very similar fragmentation patterns. Thermal decompositions are important with the tertiary chlorides especially at higher source temperatures. The rates of methanoiysis of some of these chlorides were measured. MANY WORKERS have discussed the mechanism of reactions in ion sources of mass spectrometersl and the relation between gas phase elimination of hydrogen halides from alkyl halides and SKI and El solvolytic reaction~.'".'',~ Many of these gas phase eliminations involve rearrangement of the carbon skeleton, as in the corresponding S O I V O I~S~S~~~,~~ and relative rate sequences are similar in both sets of chemical reactions.Our interest in this problem was stimulated by the analogy drawn by DeJongh and Shrader between the relative intensities of the peak due to the molecular ion, C,H,,Brf and the base peak, C,H,,+ and the rates of solvolysis of exo-and endo-2norbornyl b r~m i d e s .~ According to the kinetic approach to mass spectra using the steady state treatment: the rate of formation of C,H,,+from C,H,,Br+ should be proportional to the ratio of the recorded intensities and the relative rates were in fact similar to those found for the solvolyses, provided that allowance was made for the temperature difference between the two sets of experiments. (This treatment also ignores solvent effects and ion pair return.) Recent work, however, has shown that the ratio of daughter peak to parent depends on the accelerating voltage' and that the simple treatment is only approximate.There has been considerable work done on the fragmentation of bicyclic terpenoids,s to l1 but for the most part the terpenes themselves or their oxygenated derivatives have been studied. The study of the norbornyl bromides has been mentioned5 and it has also been shown that the mass-spectral fragmentation pattern ofendo-and exo-2norbornenyl chloride is dominated by the retro-Diels-Alder reaction.llWe have examined the mass-spectral fragmentation patterns of a number of methyl substituted endoand exo-2-norbornyl chlorides, using an MS-902 double focusing * NDEA Title IV Fellow 1965 to 1968. 81* See Appendix.

Mass spectrometry

“…Wagner-Meerwein rearrangements occur very readily in the mass spectra of several methylnorbornyl chlorides, and compounds related by these rearrangements give very similar fragmentation patterns (429). Dichlorocyclohexanes (430), monochloro alkylcyclohexanes (481) , and 1,1-dichlorocyclopropanes (482) have also been studied.…”