The principle fragmentation mode is the loss of an H-atom (M – 1) from the carbon next to the CN group due to the resonance stabilization. McLafferty rearrangement can be observed when they have longer chain lengths. The aliphatic nitro compounds normally show weak molecular ion peaks, while the aromatic nitro compounds give a strong peak. Common degradation mode is loss of NO+ and NO2+. Electrospray and atmospheric pressure chemical ionization have different rules for spectrum interpretation due the different ionization mechanisms.