Audier-Stevenson rule

The Audier-Stevenson rule allows an analyst to predict which side of the bond will keep the charge in case of bond cleavage. Consider an ionized molecule A-B+-. One must compare the ionization potentials of the radicals A and B to establish which of A or B will carry the charge in the case of the cleavage of the A-B bond. The charge will be carried by the entity whose ionization potential is the lowest. 

FIGURE 9.18 Audier-Stevenson rule applied to ionized acetone. 

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This chapter is composed of three parts. The first covers principles of thermochemistry that are fundamental to the comprehension of the mechanisms involved in spectral interpretation electronegativity, chemical bonds, acidity and basicity, inductive and mesomeric effects, the Audier-Stevenson rule, and stability rules for radicals in the gas phase. 

Figure 9.18 illustrates the Audier-Stevenson rule in the case of ionized acetone. Will the rupture of the CH3OC-CH3 bond lead to the CH3CO+ ion and to the radical CH3 (pathway a) or to the CH3+ ion and to the radical CH3CO (pathway b) The ionization potential of the radical CHjCO- (680 kJ/mol) is inferior to that of the radical CH3 (946 kJ/mol) so the latter will be ionized. 

Stevenson s Rule (Stevenson-Audier). A simple cleavage of a chemical bond in an odd electron ion may result in two pairs of ions and neutrals ... 

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