Zigzag Natta Projection

FIGURE 8.1 Linear text notation vs. Natta zigzag for 3-ethyl-3-hexanol. 

There are no formal rules for the representation of chemical compounds, although a few special cases such as steroids and carbohydrates have evolved a preferred style. This chapter will outline the revised drawing conventions used in the Combined Chemical Dictionary (CCD) (see Section 1.2.1), which other chemists may wish to follow. (CCD diagrams have, however, been added continuously over a period of nearly thirty years. This description is of best current practice.) These rules, when followed, will result in a drawing style that is consistent and unambiguous to the reader. 

The conventions adopted for CCD closely follow the International Union of Pure and Applied Chemistry (lUPAC) recommendations on graphical representation standards for chemical structure diagrams (Pure Appl. Chem., 80, 227-410, 2008) and graphical representation of stereochemical conhgurations (Pure Appl. Chem., 78, 1897-1970, 2006). Both of these publications are recommended reading for all chemists and can be downloaded via the lUPAC website. 

Organic Chemist s Desk Reference, Second Edition 

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The effective communication of chemical structure is essential for all chemists. Over the years many different types of structure representation have been developed. Before the use of computers, chemists drew structures manually, often using a linear text notation. As more sophisticated methods for drawing have become available, the trend has been toward two-dimensional stick structures, such as the zigzag Natta projection (Figure 8.1). 

Linear macromolecules having a constitutional repeating unit such as -CH2-CHX- (X 7 H) show two further stereoisomerisms, i.e., optical isomerism and tacticity. The stereoisomerism named tacticity has its origin in the different spatial arrangements of the substituents X. When we arrange the carbon atoms of the polymer main chain in a planar zigzag conformation in the paper plane, X is either above or below that plane ( Natta projection ). If the substituents X of the vinyl polymer are either all above or all below that plane (case I), the polymers are... 

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