Abstract
A rule of mass shift, which accounts for mass shifts in fragmentations of even-electron organic ions, is exemplified in detail. The term “mass shift” is defined as a mass difference between the mass of an observed ion and the mass calculated from the corresponding part of the structural formula of a sample molecule. According to the nature of the cleaved bond, the mass shift is either 0, +1, +2, or even +3 for positively charged fragment ions, and 0, -1, or -2 for negative ions. Rationalization of the rule is made on the basis of structural requirement of stable even-electron organic ions. The rule is shown to be valid not only for ordinary reactions of positive or negative ions but also for collision-induced dissociations and charge-remote fragmentations. Some mechanistic implication of fragmentations related to the rule is also discussed.
