Shape Geometric, Conformational, Topological, and Steric Properties of Drug Molecules

3 SHAPE (GEOMETRIC, CONFORMATIONAL, TOPOLOGICAL, AND STERIC) PROPERTIES OF DRUG MOLECULES 

The concept of conformational isomerism is central to any consideration of molecular shape. Molecules that are flexible may exist in many different shapes or conformers. Conformational isomerism is the process whereby a single molecule undergoes transitions from one shape to another the physical properties of the molecule have not changed, merely the shape. Conformational isomerism is demonstrated by compounds in which the free rotation of atoms around chemical bonds is not significantly hindered. The energy barrier to the transition between different conformations is usually very low 

Observations emphasize the need for extreme caution in proposing geometry-based hypotheses when dealing with drug conformations and their correlations with receptor structure, especially when the drug contains flexible acyclic hydrocarbon segments and 

Although cyclohexane is more conformationally rigid than an acyclic hydrocarbon, there are several ways to additionally stabilize or freeze the conformation of a cyclohexyl ring. 

By electrostatic repulsion of two adjoining substituents (e.g., in 1,2-dichlorocyclohexane, a diaxial conformation is forced). 

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