Stereo chemical descriptor

The fundamental principles of CAS nomenclature and the systematic CA Index Names will be briefly explained using two examples. Index Names are primarily arranged under the heading of the fiinctional parent compound, followed by the substituents in alphabetical order, the name modification to the parent compound and, finally, the stereo chemical descriptor, when necessary. The parent compound, characterized by its functional group, of the substance... 

The CAS Registry Number is shown in square brackets after each substance name and each stereo chemical descriptor. Thus the Chemical Substance Index is a rapid and inexpensive tool for ascertaining the CAS Registry Number of a particular substance in order to carry out an online search. 

Consecutive Registry Numbers are awarded to each new substance registered in the CAS Registry database. Although they contain no inherent information about the chemical composition or structure of the substance, they represent a unique identification tag for each substance and its stereo chemical descriptor. E.g. different CAS Registry Numbers are assigned to isomers, chemicals marked with isotopes or ions with different valences. It is important to know that unspecific chemicals also have a unique number ... 

Stereo-chemical molecular features (Pelosi and Persaud 2000), olfactory bulb images (Johnson and Leon 2000), and organoleptic descriptors (Dravnieks 1985). However, as rightly pointed out by Sell (2006), the complexity of the problem might make such relationships hard to uncover. 

Quantum-chemical methods (Dewar and Thiel, 1977 Dewar et al, 1985 Stewart, 1989) may be applied to obtain a large variety of stereo-electronic descriptors such as ionization potential, polarizability, electron affinity, dipole moment, charge densities, HOMO- and LUMO-energies or atomic charges using semi-empirical or ab initio calculations (Table 1.4). 

Molecular descriptors derived solely from D, E, B, and R discriminate between different basic graphs. They do not, however, differentiate between molecules such as I, II, and III with the same basic graph but with differences in their types of atoms, bonds, or stereo- and quantum-chemical features. In the remaining part of this section, a few approaches that extend basic graph descriptors to chemically informed descriptors are introduced. 

CD/ChemSketch is a freeware for drawing chemical structures including organics, organometallics, polymers, and Markush stmctures [31]. It has options for structure cleaning, viewing and naming, inch conversion, stereo descriptors etc. For freeware, no technical support is provided and the functionalities are less compared to the commercial version which has structure search capabilities (Fig. 1.5). 

Figure 13 represents a chemical structure record as It Is Input to the system. The L-number In the upper left Is the registration number. This Is followed by the molecular formula, then any stereo descriptors, reference to source, and finally the chemical structure. This Is a typical single record. The file contains approximately 135,000 such records. The year of registration Is added to the record automatically at the time of Its Input to the system. 

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