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

The solvent polarity parameter E T (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 E T (30) values is limited to non‐hydrogen‐bond donor solvents. Relationships with the chain length n are given for the determination of tertiary E T (30) values of the homologous H(CH 2 ) n Y solvent series. The parameter E T (30) is orthogonal to the function of the refractive index ( n 2 − 1) / (2 n 2 + 1). For non hydrogen‐bond donor solvents, this allows to enter E T (30) as an almost pure electrostatic parameter in a new linear solvation energy relationship. Copyright © 2014 John Wiley & Sons, Ltd.