Linear-formula notation

Wiswesser line notation The Wiswesser line-formula notation (WLN) is a method for expressing the more usual graphical structure of a chemical compound as a linear string of symbols. The resulting alternative notation is unambiguous, short and particularly suitable for computer processing and retrieval but can also be understood easily by chemists after minimal training in its use. 

There are several linear canonical notations for the input of chemical structures into the computer notable among these are the Wiswesser line notation [226] and the IUPAC notation [227], which are used in industrial information systems. In order to achieve a canonical notation, a large number of rules are necessary, more than three hundred in the Wiswesser line notation [226]. Furthermore, the resulting notation is quite arbitrary and very far from the usual practice of a chemist for example, acetone is 1V1 in the Wiswesser notation. In conclusion, both coding a formula and reading a coded formula in the Wiswesser notation require highly trained chemists. 

WLN. (Wiswesser Line-Formula notation). A system for converting chemical structural diagrams to a linear string of symbols of letters and numbers. 

There are a great number of so-called linear notations, some of them dating back to 1954 and some of them as recent as 1995, in which a chemical structure is coded as a sequence of alphanumeric characters. Only the Wiswesser Line-formula Notation (WLN) enjoys an established and widespread use within the chemical community. Its predominant role among many notational schemes is mainly because of the concerted efforts of its users to standardize and regulate the notation. Besides, WLN is easily adapted to computer processing, both for index production and structure and substructure searching. 

The summation notation formula for calculating the intercept (k(j) of a linear regression line given a set of X, Y paired data is as equation 61-24. 

The input of chemical species into the computer by means of a linear notation necessitates only standard computer devices (such as perforated cards), but requires a preliminary coding of the chemical formulae. The methods of coding will be classified according to their increasing sophistication. 

Vogin et al. [235] have created a program for the computer design of a free radical reaction mechanism in the gas phase, in agreement with the rules formulated in Sect. 2.5.3. An algorithm has been devised to transform by the computer the formula of a compound, written in the linear notation described in Sect. 6.2.1 [182], into a canonical notation. Thus, the system both preserves the flexibility of a simple natural language and gains the sophistication of a canonical notation. 

Access to all this information is provided by the Index Chemicus Registry System (ICRS), which contains records of new compounds and associated data on magnetic tape (6). Structures are described by the Wiswesser Line Notation (7), a system for describing chemical formulas in terms of a linear groups of symbols. A recent development is the ICRS Substructure Index (G5), which enables manual searches to be made for new chemical information, and is based on the occurrence of fragments of structures, the most common of which are illustrated as conventional structural diagrams. 

Formulae (13.23) form a system of linear partial differential equations of motion of a homogeneous isotropic elastic medium. These equations can be presented in more compact form using vector notation. 

In tills very general formula we are using the notation of Bishop [5], where conventionally (linear polarizability), (first-order hyperpolariz-... 

From the point of view of a computational chemist, one of the most appreciated strengths of the polarization propagator approach is that, although being generally applicable to many fields in physics, it also delivers efficient, computationally tractable formulas for specific applications. Today we see implementations of the theory for virtually all standard electronic structure methods in quantum chemistry, and the implementations include both linear and nonlinear response functions. The double-bracket notation is the most commonly used one in the literature, and, in analogy with Eq. (5), the response functions are defined by the expansion... 

Fischer projections choose the cyclic and planar, //-eclipsed conformation of the carbon skeletons of sugars as a basis, then pull the cycle straight to form a line and orient it so that the more highly oxidized end Cl is located at the top. This projection procedure remained alive for almost a century because inherent symmetry properties in carbohydrates become apparent here in the most simple way. Always remember Fischer projection formulas are the short notations of a/l-eclipsed cyclic conformations, although they look linear (Fig. 4.2.1). The terminal chiral center, C5 in hexoses, is usually R- or, in the Fischer notation, D-configured. 

The SMILES notation is a means by which certain chemical structures can be described using a series of simple letters and numbers expressed in linear fashion, even for complex cyclic structures. This approach is particularly useful as input for computer models when chemical names and CASRN are unknown. As mentioned above, SMILES is an important tool in hazard and exposure modeling used in EPA s voluntary Sustainable Futures Program [1]. It can also be used to identify substances under REACH, and examples are shown in the nomenclature Technical Guidance Document (TGD) along with molecular and structural formulas. 

Briefly, notation systems attempt to record full, multidimensional structural descriptions in a linear form, by the use of more comprehensive symbols than atoms and bonds (e.g. symbols for particular chains, rings, functional groups). Thus, more information is recorded implicitly, in Uie rides of the notation, and less is recorded explicitly in the notations for individual compounds. The rules can therefore be quite complicated, in order to ensure the notations are unique and unambiguous. For the Wiswesser Line Notation, the rules are given in Smith, E. G. The Wis-wesser Line-Formula Chemical Notation. New York McGraw-Hill 1968. In this notation, for example, saturated carbon chains are simply indicated by an arable numeral equal to the number of carbons in the chain, branch-... 

The efforts in computer technology were based on non-graphic business applications, so it was most practical for the chemical information systems to be made to adapt to the standard business computer. Systems evolved that were based on linear representations of graphical formulas, such as Wiswesser Line Notation, WLN (see Figure 3), or standard chemical nomenclature. But the linear representations were one step further removed from the 2-D structure that the chemist so depended on, and involved learning what in essence was a foreign language. The chemists found themselves more and more alienated from their own literature, and information intermediaries found their place in the sun. 

Figure 3. Linear representations of graphical formula standardized chemical nomenclature and Wiswesser Line Notation ...

The chemical notation most frequently used in this work is a linear or monodimensional (ID) notationL This type of representation has been chosen as it allows the detailed chemical formulae of the molecules and of the free radicals and the equations of reaction to be conveniently entered into the computer, and also to be printed in the same format. 

The essential characteristics of the EXGAS linear notation follow on from a simple principle an EXGAS formula must be as close as possible to a classical semi-developed formula. 

These linear alkanes are followed by the equivalent of 1 + 10, 2 -l-10, 3 + 10, etc. The prefixes are undec (11), dodec (12), tridec (13), tetradec (14), pentadec (15), hexadec (16), heptadec (17), octadec (18), non-adec (19), and icos (20). By this system, a 12-carbon straight-chain alkane is called dodecane. The seven-carbon straight-chain alkane is heptane and the 20-carbon straight-chain alkane is called icosane. The structures and names of the first 20 alkanes are shown in Table 4.1 the structures are drawn using the CH3(CH2) CHg formulas—known as condensed notation. 

---