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Mass spectral fragmentations of aminoketones in which charge is not localized exclusively on nitrogen
Author(s) -
Wagner Peter J.
Publication year - 1970
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210031010
Subject(s) - chemistry , fragmentation (computing) , ion , mass spectrum , electron ionization , aminoketone , ionization , excited state , molecule , mass spectrometry , delocalized electron , photochemistry , stereochemistry , organic chemistry , atomic physics , physics , chromatography , computer science , operating system
The low resolution mass spectra of α‐dimethylaminoacetophenone and γ‐dimethylaminobutyrophenone are compared to those of δ‐methylhexanophenone and dimethyl n ‐butylamine as well as to those of α‐dimethylaminoacetonitrile and γ‐dimethylaminobutyronitrile. Analysis indicates that significant fractions of the fragmentations of the aminoketones are directed by the carbonyl. In particular, McLafferty rearrangement of the γ‐aminoketone is favored over α‐cleavage from nitrogen at ionizing voltages below 15 eV. Although the overall fragmentation patterns are presumably determined both by the distribution of charge and by the relative rates of the fragmentation processes available to the two ionized groups, the intrinsic rates for α‐cleavage at ionized nitrogen and at ionized carbonyls appear to be very similar. Kinetic analysis suggests that 26% of the charge resides on the carbonyl in the γ‐aminoketone molecular ion. The extent of delocalization of charge in any aminoketone may be partially controlled by the extent of spatial overlap of the two groups. Correlations of mass spectral behavior with photochemical behavior are thus limited because electronic excitation is more localized in the lowest excited states of molecules than charge is in electron‐impact produced molecular ions.