Linear Solvation Energy Relationships. 12. The dδ Term in the Solvatochromic Equations

The solvatochromic equation, XYZ = XYZ0 + (π + db) is used to correlate nonhydrogen bonding solvent effects on a number of chemical properties. It is shown that d = 0 for two p - ir* electronic spectral transitions of uncharged indicators and that d is finite and negative in sign for the electronic spectral transition energy of a betaine indicator, a 19F NMR shift, a nitrogen hyperfine splitting constant in an ESR spectrum, an infrared ∆vp-spectral shift (in solvent relative to gas phase), and in a fluorescence spectrum. It is suggested that d = 0 for p ↖ π spectral transitions is a limiting condition (i.e., d is seldom, if ever, positive). The empirically derived solvatochromic parameters are related to more fundamental properties of the solvents. © 1981, American Chemical Society. All rights reserved.