Contribution of groups

This approach is obviously simplified but can only be improved when there is much more data available than in this specific case. This enriched approach was not possible given the poor bibliographical source. It was made possible because of availability of current databases. The rules presented here are nevertheless sufficient since the published AfT are not very accurate. The table below gives the contributions of groups that could be determined. It is Impossible to have access to all types of structures since some of them are not well documented enough for the time being. 

From the retention volume for some compounds consisting of different number of the same groups it is possible to determine the contribution of groups to the retention by solving system of linear equations (1). 

The contribution of groups or fragments to the retention volume at different temperatures (Vai) can be calculated from the retention volumes of compounds at the same temperatures (Va) and then the contribution of groups to the heat of adsorption from equation ... 

On the other hand the heat of adsorption of compound can be presented as sum of the contribution of groups to the heat of adsorption. 

The contributions of groups or fragments of molecules to the retention volume (Vai, cm /m )... 

Contribution of Group Adsorption Energies to Sample Adsorption. The Martin Reiationship... 

Contribution of Group Adsorption Energies to Sample Adsorption. 

UNIFAC is an extension of UNIQUAC, in which the interaction parameters are estimated by means of contributions of groups. Firstly, the molecules are decomposed in characteristic structures, as functional groups and subgroups. Some small molecules are considered separately for more accuracy. Then the parameters involved in UNIQUAC-type equations are determined, as follows ... 

The UNIQUAC method requires complete calculation in each specific case. Now, though, we are going to examine the concept of the contribution of groups, which can be used to calculate certain properties of the molecules a priori, using relatively small databases, and the application to a model to calculate the excess Gibbs energy a priori. 

The concept of the contribution of groups is based on the idea of additivity. Some of the properties of a molecule can be expressed by a weighted linear combination of the contributions of the groups of atoms making up the molecule. 

Solubility parameter theory was advanced first by Hildebrand and Scott. Small developed a method for calculating the parameters from the contributions of groups within the molecule. Bunell, Hansen, and Crowley et al. were especially successful in utilizing the concept for the formulation of solvent-based... 

The effect of a para substituent reflects both inductive and resonance contributions to the carbon atom bearing the carboxyl group. The effect of a meta substituent results only from inductive effects. The contribution of groups ortho to the carboxyl group is not easily interpreted because of steric effects on the conformation of the carboxyl group as well as solvation effects. 

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