The Computation of MCB and MCA Scales

The performance of theoretical methods to compute gas-phase cation basicity and/or affinity scales can be evaluated using Equation 6.25  

There are no such systematic theoretical studies concerning a comprehensive series of ligands for the other cations selected in this chapter. The interested reader is referred to the publications listed for these cations in Section 6.5. These papers often combine experimental and theoretical determinations. 

MCA and MCB scales (Tables 6.3-6.15) are the source of numerous structure-basicity relationships in the field of cation/ interactions. The following sequences of basicity (affinity) are observed in the comparison of benzene with  

The last sequence can be made quantitative by means of the field, resonance and polarizability constants of the ring substituents, crp, and a a [215], respectively  

Regression coefficients of expression 6.26 show that the lithium cation/7r interaction is affected almost equally by the field and resonance effect of the ring substituent and that the polarizability effect is smaller, although significant. 

---