General Quantitative Structure-Property Relationship Treatment of the Refractive Index of Organic Compounds

The refractive index (n) is one of the most important optical properties that is frequently employed to characterize organic compounds.1 The refractive index is defined as a ratio of the velocity of light in a vacuum to the velocity of light in the substance of interest. It has been used as an indicator of the purity of organic compounds, but the relationship of refractive index to other optical, electrical, and magnetic properties has more significance. The relationships between refractive index and polarizability, critical temperature, surface tension, density, boiling point, among other properties, have been reviewed by Partington.2 Refractive index is also widely used in material science to evaluate materials.3 Most theoretical treatments for the prediction of refractive index (n) have been developed in terms of molar refraction, which quantifies the intrinsic refractive power of the basic structural units of a material. Alternative definitions of molar refraction (R) have been proposed by Lorentz and Lorentz4,5 (eq 1), by Gladstone and Dale6 (eq 2), and by Vogel7 (eq 3).