The behaviour of a number of deuterated imidazoles upon electron-impact has been studied. Loss of H' from the molecular ion occurs specifically at the 4(5)-position. Loss of HCN is less specific, the order being 2 > 4(5) > 1.

[C,H,N]? ions generated from a number of different precursors have been studied by high kinetic energy ion-molecule reactions. It has been shown that at least four distinct stable species occur, of which acetonitrile and methyl isocyanide retain their original structure. With imidazole or pyrazole as precursors, a mixture of open chain radical cations, not identical to the above species and probably interconvertible via the 1H-azirine radical cation, is formed. From butyronitrile, pyrrole, crotonitrile, ally1 cyanide, methacrylonitrile and cyanocyclopropane a fourth species, probably the vinylidenimine ion, is formed

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The mass spectra of aU isomers of methylnibopyrazoles are reported. Generally, the spectra are charactenstic of nitropyrazoles. In some cases however, o d o eñects occur, recognizable by primary losses of, for example,

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Abstract. Nitration of 2-tert-butyl-and 2,7-di-tert-butylpyrene affords molecules with severely hindered nitro groups. A nitro group ortho to a tert-butyl group is twisted at least 82" out of the plane of the aromatic nucleus. The lack of interaction between the hindered nitro group and the aromatic system is reflected in the chemical behaviour, as well as in the spectroscopic properties, of these nitro derivatives. Upon fragmentation in the mass spectrometer, the tert-butyl group is always replaced by a hydrogen atom. Nitro groups are only replaced by a hydrogen atom if they are ortho to a tert-butyl group.

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