Stereochemistry terminology

Every new class of reactions (additions, eliminations, substimtions, etc.) has its own terminology for stereochemistry. As you learn each of these classes of reactions, keep a watchful eye on what terminology is used to describe the stereochemistry. Then, look at the mechanism of each reaction within each class, and try to understand how the mechanism explains the stereochemistry. 

In addition to the regiochemistry, there is also special terminology used to describe the stereochemistry of a reaction. As an example, consider the following simple alkene ... 

JP Moss. Basic terminology of stereochemistry. Pure Appl. Chem. 68, 2193, 1996. 

Basic Terminology of Stereochemistry hitp //www,chem.qmut.ac.uk/iupac/siereo/ Enzyme Nomenclature http //www.chein.qimil.ac.uk/iubmb/enzyme/... 

Within the commonly accepted terminology of stereochemistry, molecular shape is understood as being the three-dimensional arrangement of formal chemical bonds. Most approaches toward the visualization of stereochemical arrangements of atoms... 

Before we attempt to answer the above questions, we need to examine briefly the terminology relevant to a discussion of chiral drugs. Specifically, the definition and usage of two important terms need to be clarified. Chiral was defined in one recent leading monograph on stereochemistry as follows Not superposable. .. with its mirror image, as applied to molecules, conformations, as well as macroscopic objects, such as crystals [3]. Mislow gave a shorter but essentially equivalent definition An object is chiral if and only if it is not superposable on its mir-... 

In the diamond stmcture, carbon atoms are present in sp hybridization, with a tetrahedral stereochemistry and a face-centered cubic stmcture that is shown in Fig. 2.1. Besides natural diamond, synthetic diamond has been produced since General Electric first announced its successful high-pressure synthesis in 1955. Sintered polycrystalline diamond, different types of diamond films, and diamondlike carbon are other types of diamond-related synthetic materials, some of which are noncrystalline [13, 19] these solids have their own terminology [10, 20]. Unhke other carbonaceous solids, diamond has a rather limited and specific relevance to adsorption. Indeed, ever since the publication of a pioneering work... 

The terminology and notation that have been used to describe coordination compounds have been derived with one notable exception from the terms and symbols developed to describe the stereochemistry of carbon compounds. The terms ois, trans endo, exo dextro, d, D, (+) and leva, l, L (-) all have been used to describe the stereochemistry of coordination compounds in a close analogy with organic compounds (see Figure 1). As the descriptions of the chemistry and structures of coordination systems have become more varied and complex, the meanings of these terms have become less precise, as in the example of a ois or trans tricarbonyl octahedral compound (see Figure 2). The terms fao and mer were coined to indicate the facial and meridional disposition of substituted octahedral structures. 

Geometric isomers of linear quadridentate ligands on octahedral compounds are recognized to exist in one trans and two ois forms (see Figure 3). The ois compounds are generally referred to as the a and B forms. In these examples we can see that the terminology developed to denote the relatively simple tetrahedral and planar carbon stereochemistry is not adequate when applied to the stereochemistry of octahedral compounds. 

The relative ranking of ligands for the description of the stereochemical properties of a molecule is the most utilized and accepted principle throughout stereochemical nomenclature. This is not yet the practice, however, in discussing the stereochemistry in coordination and inorganic chemistry. In the context of coordination and inorganic chemistry, stereochemical information is either presented in the more traditional terminology, or more often by means of a stereospecific structural representation. 

Most organic molecules in living organisms contain asymmetrical centers (i.e., they are chiral). (The terminology of stereochemistry has been reviewed by Moss.1) For example, amino acids that are incorporated into proteins are L and sugars in carbohydrates are D. It is understandable that the three-dimensional structures of the receptors in proteins for small molecules will favor only one optical isomer (i.e., the one that fits sterically, hydrogen bonds properly, and so on). Most compounds made for use by plants and animals will have to be single optical isomers. 

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