Group Additivity Principle Research Articles

Freezing temperatures and enthalpies of dilution of aqueous solutions of amides. Gibbs energies and enthalpies of interaction of the N,N-dimethylamide group in aqueous solutions

Enthalpies of dilution, freezing temperatures, and densities of aqueous solutions of N,N-dimethylacetamide and N,N-dimethylpropionamide have been measured. Freezing temperatures of dilute aqueous solutions of formamide and N,N-dimethylformamide have also been measured. These data yield the pairwise molecular Gibbs energies and enthalpies of interaction: these have been treated according to a group additivity principle to give pairwise functional group Gibbs energies and enthalpies of interaction. The results indicate that substitution on the amide nitrogen may increase the Gibbs energy and enthalpy of interaction of the amide group with itself in an aqueous environment but the effect if present is small.

Paper chromatography and chemical structure : VII. The separation of meta- and para-derivatives of benzene

The separation of m- and p-disubstituted benzene derivatives has been studied in four systems. It is shown that the R M values of these compounds cannot be correlated with the existence of charge separations or with the vectorial dipole moment. The p-isomers generally obey the group additivity principle, whereas m-isomers, when they differ, depart from this principle. The separation of m- and p-isomers is explained in terms of a competition between intra- and intermolecular hydrogen bonding. It is shown how in m-isomers, the presence of an ortho/para-directing group can affect hydrogen bonding by inducing a fractional negative charge on the para-carbon atom. Benzene derivatives containing two meta-directing groups appear to be inseparable by partition chromatography, and this is discussed. Certain compounds, such as substituted anilines, have anomalous R M values and may contain, in hydroxylic solvents, small amounts of compounds of the type, RNH 3+OH−. The chromatography of halophenols shows no influence of the inductive effect of the halogens; they separate according to their molar volume. There was no ortho-effect in halophenols in the reversed phase system studied, confirming that this effect is not spatial but mainly polar in origin.

Paper chromatography and chemical structure: VII. The separation of meta- and para-derivatives of benzene

The separation of m- and p-disubstituted benzene derivatives has been studied in four systems. It is shown that the RM values of these compounds cannot be correlated with the existence of charge separations or with the vectorial dipole moment. The p-isomers generally obey the group additivity principle, whereas m-isomers, when they differ, depart from this principle. The separation of m- and p-isomers is explained in terms of a competition between intra- and intermolecular hydrogen bonding. It is shown how in m-isomers, the presence of an ortho/para-directing group can affect hydrogen bonding by inducing a fractional negative charge on the para-carbon atom. Benzene derivatives containing two meta-directing groups appear to be inseparable by partition chromatography, and this is discussed. Certain compounds, such as substituted anilines, have anomalous RM values and may contain, in hydroxylic solvents, small amounts of compounds of the type, RNH3+OH-. The chromatography of halophenols shows no influence of the inductive effect of the halogens; they separate according to their molar volume. There was no ortho-effect in halophenols in the reversed phase system studied, confirming that this effect is not spatial but mainly polar in origin.