Über Pyridinium‐N‐phenolat‐Betaine und ihre Verwendung zur Charakterisierung der Polarität von Lösungsmitteln, XVI. Bestimmung der empirischen Lösungsmittelpolaritäts‐Parameter ET(30) und AN für 55 substituierte Phenole

Pyridinium N‐Phenoxide Betaines and Their Application for the Characterization of Solvent Polarities, XVI1). – Determination of the Empirical Parameters of Solvent Polarity ET(30) and AN for 55 Substituted Phenols By means of the negatively solvatochromic dyes 1 and 2, the empirical solvent polarity parameters ET(30) and AN (Acceptor Number) are determined for solutions of 55 substituted phenols in 1,2‐dichloroethane as inert solvent (Table 1). The ET(30) values and Acceptor Numbers are compared with each other and with corresponding literature values, determined in neat substituted phenols (Table 2). The influence of the phenolic substituents on both solvent parameters is discussed with respect to their electronic and steric effects as well as to the self‐association of phenols in solution. Polyhydroxybenzenes such as resorcinol and pyrogallol exhibit both high solvent polarity and acceptor properties, whereas substituents in positions 2 and 6 of phenols decrease their polarity and acceptor strength.