Optical rotatory power of organic acids and their derivatives in aqueous and non-aqueous solutions

The rotations of &- (X -n-butyl-propionic acid and its methyl ester have been examined in various organic solvents, and correlated with the refractive indices of the media, in the sense that a relatively high refractive index corresponds to a relatively low rotation. This relationship is subject to constitutional influences: for example rotations of tho ester in solvents of the benzene type are higher than the values expected from refractive index considerations as applied to the methane type of solvent, but in each group separately, the Inverse relationship between refractive index and rotatory power is in general respected. In certain instances the dipole moment of the solvent exerts a modifying influence, a high dipole moment tending to raise the rotation. Examination of those and other factors has led to the conclusion that the dextrorotatory acid and ester possess an L - configuration.In aqueous and aqueous-alcoholic solutions of d- α -n-butyl-propionic acid and its sodium salt, it is considered that the effect due to variation in refractive index is snail in relation to the changes produced by ionisation, association and solvation. Association and solvation are taken as raising the rotation, while ionisation lowers it.The rotations of tartaric acid and Its sodium, ammonium and tetra-ethyl-ammonium salts have also been examined in aqueous and aqueous-alcoholic solutions, and discussed on similar principles. Contrary to d- butyl-propionic acid, the dextrorotatory tart¬ aric acid is associated with a D- configurations ioni3ation now raises the rotation while association and solvation lower it. For the given conditions the effect of the variation in the refractive indices of the media is regarded as negligibly small. The data given for aqueous solutions of salts of tartaric acid have been discussed on the assumption that two main influences act in opposition, one bearing on the relative rotations of undlssociated salt and solvated anion, and the other exemplified by the known effects of positive ions on non-lonisable molecules containing hydroxyl groups