Structural notation

The cP4-AuCu3 type an example of the use of alternative and complementary structural notations and symbols... 

It has become increasingly popular to represent [C5H5]- by the structure shown in Fig. 6d. This representation is a valence bond structure notation it is intended to represent the five equivalent resonance structures (three of these are shown as Figs. 6c, /, and g the other two are similar), in which the negative charge is located at each carbon in turn. Each double bond is thus only a partial double bond and, if the usual notation of writing a partial double bond by a dashed line were applied, the structure would be written as 6h. The solid circle (6d) is a rapid way to write the 66 structure. In a completely analogous... 

The Lewis structure notation is useful because it conveys the essential qualitative information about properties of chemical compounds. The main features of the chemical properties of the groups that make up organic molecules, ... 

Some years ago in a continuing effort to understand phase diagrams, I had discovered [3] the following empirical rules among more than 300 binary phase diagrams reported in the literature (Hansen, Elliot Shunk) [4,5,6], The metallic radii, Ra, Rb, used are from INTERATOMIC DISTANCES (The Chemical Society, London, 1958) [7] and the structural notation follows that described in Handbook of Lattice Spacing and Structure of Metals (Pearson, 1958) [8]).. 

Goodwin has provided a useful summary of the structural chemistry applicable to the retinoids of vision36. However, the book is not as comprehensive as needed to address all of the types of Vitamin A. He also refers to a separate essay on the structural notation he uses37. Taylor Ikawa have provided additional nomenclature, more semisystematic names and excellent information on laboratory evaluation techniques38. 

However, it is not significant in the natural formation of the molecules. If the number 11 carbon of the suggested serial systematic notation (number 5 carbon of the -ionone ring using the structural notation of the IUPAC) is considered a member of the isoprene chain for the purposes of synthesis, the material in Spom et. al. relative to modifications to the Chain is probably useful. 

In order to calculate a physicochemical property, the structure of a molecule must be entered in some manner into an algorithm. Chemical structure notations for input of molecules into calculation software are described in Chapter 2, Section VII and may be considered as either being a 2D string, a 2D representation of the structure, or (very occasionally) a 3D representation of the structure. Of this variety of methods, the simplicity and elegance of the 2D linear molecular representation known as the Simplified Molecular Line Entry System (SMILES) stands out. Many of the packages that calculate physicochemical descriptors use the SMILES chemical notation system, or some variant of it, as the means of structure input. The use of SMILES is well described in Chapter 2, Section VII.B, and by Weininger (1988). There is also an excellent tutorial on the use of SMILES at www.daylight.com/dayhtml/smiles/smiles-intro.html. 

Two facts stand out from all experience in notation and nomenclature the urgent necessity for a rigid systematic nomenclature for organic compounds and the essentiality of a one-one correspondence between structure, notation, and nomenclature. Perhaps no system of notation or nomenclature will be other than a dead letter unless it follows the natural line of thought of the user, and does not depart too much from his common habits of expression. Th at great scientist, Lord Rayleigh, said ... 

All structural notations attempt to give some indication of the real-life arrangement of the atoms within the molecule in question. The notations fall into two categories two-dimensional and three-dimensional. The former type portrays the molecule as though it were flat, and leaves unresolved any explicit information about the three-dimensional structure. This type only indicates the connectivities of the component atoms to each other. In contrast, the latter type sets out to give as much information as is possible on a flat sheet of paper of the spatial configuration of the constituent parts of the molecule in question. 

This structural notation is very cumbersome. It is used only when it is necessary to illustrate the origin of each electron in a covalent bond. A dot is used to indicate an electron originating from one type of atom, while a cross is used for an electron originating from a different type of atom. It is used only for very simple molecules. 

Polystyrene is the name of a homopolymer made from the single monomer styrene. When the name of a monomer comprises two or more words, the name should be enclosed in parentheses, as in poly(methyl methacrylate) or poly(4-bromostyrene) to identify the monomer more clearly. This method can result in several names for a given polymer thus, poly(ethylene glycol) , poly(ethylene oxide) and poly(oxirane) describe the same polymer. Sometimes, the name of a hypothetical monomer is used, as in poly(vinyl alcohol) Even though a name like polyethylene covers a multitude of materials, the system does provide understandable names when a single monomer is involved in the synthesis of a single polymer. When one monomer can yield more than one polymer, e.g. 1,3-butadiene or acrolein, some sort of structural notation must be used to identify the product, and one is not far from a formal structure-based name. 

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