Topological aspects of molecular interactions in liquid mixtures of non-electrolytes
It has been shown that activity coefficients of the components of an Ci+j) mixture have a simple topological base and that t he same (as well as G'(T,XL) and HE(T,xi data) can be welb predicted, on the strength of graph-theoretica l arguments when only H (T,xL=0.4 and 0.5) data f or the binary m ixture, of almost e qual sized components, are available. For Ci+j) mixtures that a re characterized by the presence of 1:l or 1:l and 1:2 molecular complexes or have components that differ appreciably in molar volumes the approach has been modified to well reproduce the activity c oefficients d ata when datum alone is available for the mixture. The versatility of graph-theoretica l arguments have further been made evident by rationalizing volumetric and ethalpic e ffects in (i or ifS) fi.e. i saturated with a salt (S)) fi+j) mixtures to yield worthwhile insight into i) the molecular state of i and or j for of the salt S in i and the influence of j on it) and ii) the energetics of molecular interactions that characterize these mixtures. Solution non-ideality has been attributed (ref.1) to either physical intermolecular forces or to chemical reactions between the components of Ci+j) mixtures. S ince laws of limited validity (ref. 2) have been employed to describe intermolecular potential functions that characterize interactions between the components of these mixtures, almost all the present theories (ref. 3-91 of solutions of non- electrolytes have limited applicability. Again the process of binary mixture formation may trigger inter or intramolecular changes in either one or both the components and this must begreflected in the molar excess volume VE and molar excess e nthalpy H data. In this regard a lthough, a few recent approaches (ref. 10-13) address themselves specifically to this aspect of molecular interactions, yet t hey require that the molecular states of the pure components be known and that a proper itinery be maintained of the various entities that exist in these mixtures; this may not be possible always. This calls for an alternative. approach. Topological aspects of the activity coefficients of the components of a (i + j) mixture: conceptual aspects of approach and results The structural formula of chemists is actual1 a molecular graph (ref.14)characterized by vertices (atoms) and edges (bonxs) G(e,v). If the pure i and j are represented by Gt (e~ ,y4 1 (or G; 1 and G. (e. v. 1 (or G. 1 respectively, then the fi+j) mixture formation dwodlh 'be charadterized by interactions between i and j in the GLx Gi molecular graph (ref. 15). As activity c oefficient of, say, the i th component