Shorthand chemical structures

Another name for isoprene is 2-methyl-1,3-butadiene. When illustrating the reactions of isoprene it is convenient to use the shorthand chemical structure (see Table 2.12),... 

The commercial 2D structure editor. Chemistry 4D-Draw, from Chemlnnovativc Software Inc., includes two additional special modules besides conventional chemical drawing tools. NamExpert provides the interpretation ofa compound name according to the lUPAC nomenclature to create the corresponding chemical structure. The latter can be represented in three different styles the shorthand. Kckulc. or semi-structural formula. In contrast to NamExpert, the Nomenclature module assigns lUPAC names to drawn structures. 

Process Flow Chart. Gives the sequence of reactions in chemical structure terms. Nomenclature. Provides an index linking the chemical structure of the intermediates and API with the shorthand designations used by the company and the Chemical Abstracts Name. 

Although almost any a-amino acid might be used, natural proteins are constructed from only about 20 different amino acids, and the group R is never very large (Table 10.7). The nature and sequence of these amino acids determines the primary (chemical) structure of the protein. A shorthand notation is frequently used to portray this primary structure as, for example, in... 

The following shorthand designation may be used to describe the chemical structure of fatty acids the number of carbon atoms in the chain separated by a colon from the number of unsaturated bonds is followed by a set of parentheses containing the numbers of the double-bond positions and the letters c, t, or a to indicate whether a bond is cis-olefinic, trans-olefinic, or acetylenic. The position of double bonds is numbered from the carboxyl group. 

The systematic name of this compound, is cis-9-octadecenoic acid, also termed in the shorthand nomenclature 18 1 or 18 l(i -9). The chemical structure of oleic acid is depicted in Figure 9.1. 

The diagrammatic representation of chemical structures is a compact and essential communication tool for chemists internationally, and has been employed for centuries as an accurate notational shorthand. Substantial research efforts have been, and continue to be, invested in the development of efficient and effective methods for the computerized storage and retrieval of these structures. In recent years this has grown to encompass the description of the three-dimensional (3D) model of the chemical substance as well as the two-dimensional (2D) structural diagram. 

All of these chemical species have importance in the production of polymeric materials. There are several shorthand techniques for writing down the structures of polymers. The carbon-based polymer molecules using the stick representation are made up of atoms connected by covalent bonds (represented here by the straight lines between the carbon and the hydrogen and the carbon-to-carbon molecules), as shown in Fig. 2.6. To reiterate, carbon is always tetravalent, having four covalent bonds, and a schematic of the paired electrons for two of the incorporated carbon molecules can be seen in the bottom of Fig. 2.6. Thus each stick represents two electrons. For the two highlighted carbon atoms in the polyethylene molecule of Fig. 2.6, the electron representation is shown, where there are four covalent bonds associated with each carbon and each bond is made up of two shared electrons represented by the black dots. This polymer molecule is made up of only carbon and hydrogen with no double bonds, and it represents a linear form... 

In the remainder of this chapter, specific examples of fibrous minerals are presented. The chemical formulas are given as well as the mineral names. A formula is a shorthand notation that describes the elemental composition of the compound plus the specific ion associations, as determined by three-dimensional structure analysis of the species. Because every mineral sample is not completely analyzed, an ideal formula—one that summarizes the chemistry and associations of the ions—is usually presented. 

In the preceding simplified structural formula for benzene the six hydrogen atoms have been omitted. Resonance between the two possible arrangements of the three double bonds1 is indicated by the circle. Chemical shorthand of the following type is used throughout the book. Carbon atoms may be represented by an angle or the end of a line, but other atoms will always be shown. 

The structural formula is also a shorthand notation for the important chemical reactions of lhe compound. Ii can be considered as being built up of a group of organic radicals, i.e.. groups of atoms that retain their individuality in the course of certain reactions. Each radical has reactions which are characteristic of its presence in the molecule. 

Lewis structures can be used to help determine the ratio of the atoms in a compound. To communicate this ratio, chemists use a special kind of shorthand called a chemical formula. A chemical formula provides two important pieces of information ... 

Electron-dot structures Because valence electrons are involved in forming chemical bonds, chemists often represent them visually using a simple shorthand method. An atom s electron-dot structure consists of the element s symbol, which represents the atomic nucleus and inner-level electrons, surrounded by dots representing the atom s valence electrons. The American chemist G. N. Lewis (1875-1946), devised the method while teaching a college chemistry class in 1902. 

A structural formula of a compound is not only a representation of the space relationships of atoms and electrons it is also a shorthand description of methods available for its synthesis and of the chemical and physical properties of the compound. 

The simplest LEED patterns are most frequently characterized by a shorthand notation in which the unit cell of the surface structure is designated with respect to the bulk unit cell. An arrangement of surface atoms (the surface net ) identical to that in the bulk unit cell is called the substrate structure and is designated (1 x 1). For example, the substrate structure of platinum on the (111) surface is designated Pt(lll)-(1 X 1). If the surface structure that forms in the presence of an adsorbed gas is characterized by a unit cell identical to the primitive unit cell of the substrate, the surface structure is denoted (1 x 1)-S, where S is the chemical symbol or formula for the adsorbate. For example, a monolayer of oxygen adsorbed on the (111) face of silicon is denoted Si(l 11)-(1 X l)-0. 

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