Simple Relationships for the Estimation of Melting Temperatures of Homologous Series

Abstract

The melting behavior of a homologous series is described in terms of the melting of the parent molecule and of the polymer the series eventually forms. For those series characterized by a parent melting below the melting temperature of the related polymer, the melting behavior can be described quantitatively by the hyperbolic functionwhere T f (n) refers to the melting temperature of a compound with n repeat units, T f (∞) is the melting temperature of the polymer, and m and b are two variables used in fitting the data. A plot of [1/(1 -T f (n)/T f (∞))] against n results in a straight line with slope m and intercept b. This linear relationship provided the analytical form of the equation described above. For series with parents exhibiting melting temperatures higher than those of the related polymer, a linear correlation is observed when]. These equations appear applicable for the quantitative evaluation of the melting behavior of any homologous series, provided care is taken to consider compounds characterized by the same symmetry number. Molecules containing odd and even numbers of repeat groups are generally treated separately. The hyperbolic behavior exhibited by the melting temperature in most series appears characteristic of molecules that seem to pack similarly in the solid state. Series with members exhibiting liquid-crystal behavior are successfully modeled by these equations, provided the transition correlated is the temperature at which the liquid becomes isotropic. The usefulness of these equations was tested by selecting three data points from each series to provide values for m and b. The melting temperatures of most compounds in the series were estimated using these parameters. This resulted in a standard deviation of (6.6 K between experimental and calculated values based on a total of 995 compounds.

Odd–even effect in melting properties of 12 alkane-α,ω-diamides

“…As expected, both even and odd terms appear to converge in the limit to the melting temperature of polyethylene [8,40]. Moreover, the hyperbolic behaviour exhibited by the melting temperature in most series seems to be characteristic of molecules that pack similarly in the solid state [40].…”

“…Besides, it is worth noting that T fus of even diamides can be modelled quite well by a hyperbolic function depending on the number of methylene groups in the molecule, as in the case of other homologous series, such as hydrocarbons, cycloalkanes, functionalised alkanes, and symmetrically substituted derivatives [40]. As expected, both even and odd terms appear to converge in the limit to the melting temperature of polyethylene [8,40].…”

Estimating fusion properties for functionalised acids

“…method gives a very large error on the fusion temperature. This can be ascribed to the fact that this method considers T fus as a sum of group contributions -while it is actually not a group property (Chickos and Nichols, 2001)-, resulting in large overestimations for larger molecules (e.g. 275 K for citric acid).…”

Thermodynamics of fenoxycarb in solution

“…More complex methods include classical Quantitative Structure-Property Relationship (QSPR) modelling [8], group contribution methods [9] and correlating similar compounds [10]. Prediction of the solubility at different temperatures is done by the Hildebrand-Scatchard models [11], as well as several methods that involve experimentally obtaining one or more solubility data points [6; 12].…”