Electron-impact mass spectrometry for location of epoxide position in long chainvic-dialkyl and trialkyl epoxides

Plots of percent abundance vs m/e for selected series of ions (differing by 14 mass units) obtained by low resolution mass spectrometry allowed the epoxide position to be located in 30 C₁₇?C₂₁vic-dialkyl and trialkyl epoxides. Major diagnostic fragmentations are as follows. In thevic-dialkyl epoxides of the study, fragments useful for determining epoxide position result from α-cleavage, and epoxide position may be recognized by the maxima obtained in a plot of percent abundance vs m/e values in the C_nH_2n?1O series (113, 127, 141 ….); a similar plot of percent abundances vs m/e values in the C_nH_2n?2 series (110, 124, 138 ….) also shows maxima for ions corresponding to those obtained by transannular cleavage plus water elimination. In the trialkyl epoxides, fragments most useful for locating epoxide position are those obtained from ions corresponding to α-cleavage plus H-transfer; epoxide position may, thus, be recognized by the maxima obtained in a plot of percent abundance vs m/e values in the C_nH_2nO series (72, 86, 100 ….). Transannular cleavage with H-transfer produces C_nH_2n+1O products (m/e 115, 129, 143….), with the fragment containing the methyl substituent being much more abundant.