Solvent polarity scales: determination of new ET(30) values for 84 organic solvents

The solvent polarity parameter ET(30) is newly measured from the solvatochromism of the betaine dye 30 for 84 solvents and re‐measured for 186 additional ones. The results are organized in a database. It is shown that the validity of linear solvation energy relationships used for the determination of secondary ET(30) values is limited to non‐hydrogen‐bond donor solvents. Relationships with the chain length n are given for the determination of tertiary ET(30) values of the homologous H(CH2)nY solvent series. The parameter ET(30) is orthogonal to the function of the refractive index (n2 − 1) / (2n2 + 1). For non hydrogen‐bond donor solvents, this allows to enter ET(30) as an almost pure electrostatic parameter in a new linear solvation energy relationship. Copyright © 2014 John Wiley & Sons, Ltd. By means of solvatochromic betaine dyes, solvent polarity parameters ET(30) of 84 organic solvents are newly determined, and 186 are re‐measured. Linear solvation energy relationships used for the determination of secondary values are shown to be strictly valid only for non‐hydrogen‐bond donor solvents. These findings allow the construction of a database of 270 reliable ET(30) values.