Structural Aspects

The various polymorphs of an organic compound (e.g. those shown schematically in Figure 1(A)-(C)), are characterized by different sets of intermolecular interactions (e.g. van der Waals forces, hydrogen bonding, X-H interactions, where X = C, N, O typically). For molecules containing hydrogen bond donor and acceptor groups, the incidence of polymorphism generally increases owing to the variety of ways in which such molecules can self-

assemble to form supramolecular arrays. Figure 6 shows portions of the crystal structures of two poly-morphs of the drug paracetamol. Despite similar molecular conformations, the intermolecular relationships differ very significantly as a result of the different hydrogen bonding arrangements adopted. Ultimately, it is these features which determine all the observed differences in the physical properties of these polymorphic forms.

Prediction of the crystal structure (or rather, of the family of possible polymorphic structures) of an organic compound from a knowledge of the molecular structure alone is considered a highly desirable goal, but the current state of knowledge of the nature of intermolecular interactions generally prevents its achievement. As to prediction of the outcome of polymorphic crystallization, it would be necessary to invoke additional considerations of thermodynamic, kinetic and solvent effects. These problems are currently being addressed by computational methods with moderate success.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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