On Solvent Basicity:  Analysis of the SB Scale

The solvent basicity (SB) scale, introduced by Catalán et al. in 1996, was compared with theoretical data (V min and εmo(Vmin)), calculated at the HF-SCF 6-31G** level, and with experimental data (ΔH f of Arnett, δΔH solv of Laynez, ΔΔν̃(1)−(2) and ΔΔν̃(3)−(5) of Laurence, and ΔH g→solvent for SO2 and I2 of Benoit and Louis). The fact a SB scale is a family-independent scale results in no grouping of the solvents in parallel lines. As also shown by the results, a basicity scale constructed around a standard phenolic Brönsted acid (R-OH) such as 4-nitrophenol or 4-fluorophenol is more correct than one based on an unsubstituted amine such as 4-nitroaniline. The SB scale has a near-unity covalent-to-electrostatic ratio, so it is sensitive to both covalent and electrostatic interactions and hence approaches closely the requirements for a general basicity scale.