Structure-property relationships in organic solid forms : structures and melting points

Ding, Yuanxin (2007) Structure-property relationships in organic solid forms : structures and melting points. University of Southampton, Doctoral Thesis.

Abstract

An exploration of the correlations between melting point and molecular and crystal structures has been made.  The research was based on a training set with 100 compounds in which the molecular structures contain one common, core unit with two various  terminal groups.  Previous work by Dr Gelbrich of our group confirmed that the crystal structures of the training set comprise 56 different structure types containing nine different types of hydrogen bonding arrangements.

The investigation was divided in three main parts which focused on (1) the effect of molecular structures on melting point, (2) the influence of different crystal structures on melting point and (3) a statistical approach to the correlation of melting point with chemical descriptors derived from molecular and crystal structures.

Part one focused on exploring how the two terminal groups affect a compound’s melting point.  The result showed that NO₂, CN and I groups at both R₁ and R₂ positions cause a high meting point whilst MeO, H and F are related to the low melting point samples.

In part two, the crystal structures of compounds with two dominant types of H-bond were explored.  The detailed analysis involved attempting to identify and assess all potential intermolecular interactions.  Moreover a two-dimensional fingerprint plot generated from Hirshfeld surface has been used to give a better understanding on intermolecular interactions within a crystal structure.

In part 3, three melting point prediction equations based on molecular descriptors (R²=41.70%, S=28.5056), crystal structure descriptors (R²=37.00%, S=29.1297) and combined descriptors (R²=54.10%, S=25.4277) respectively.

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