Connectivity line formula

Bond-line formula (Section 1.7) Formula in which connections between carbons are shown but individual carbons and hydrogens are not. The bond-line formula... 

For more electropositive elements, which have an inferior number of valence electrons in the first place, and which in addition have to supply electrons to a more electronegative partner, the number of available electrons is rather small. They can gain electrons in two ways first, as far as possible, by complexation, i.e. by the acquisition of ligands and second, by combining their own atoms with each other. This can result in the formation of clusters. A cluster is an accumulation of three or more atoms of the same element or of similar elements that are directly linked with each other. If the accumulation of atoms yields a sufficient number of electrons to allow for one electron pair for every connecting line between two adjacent atoms, then each of these lines can be taken to be a 2c2e bond just as in a common valence bond (Lewis) formula. Clusters of this kind have been called electron precise. 

The alkane series is also called the saturated hydrocarbon series because the molecules of this class have carbon atoms connected by single bonds only, and therefore have the maximum number of hydrogen atoms possible for the number of carbon atoms. These substances may be represented by the general formula C H2,I + 2 and molecules of successive members of the series differ from each other by only a CH2 unit. The line formulas and names of the first 10 members of the series, given in Table 21-2, should be memorized because these names form the basis for naming many other organic compounds. It should be noted that the first parts of the names of the later members listed are the... 

The constitution is customarily represented by constitutional formulas, i.e. by labelled graphs whose nodes are the atoms, and whose connecting lines are the bonds. Nodes are labelled by chemical element symbols and can carry further symbols for electrons and electrical charges. 

In line formulas, each line segment represents a C-C bond, and C-H bonds are not shown (see Sec. 1.10). There are a number of acceptable line structures for Ch Ch Ch, three of which are shown here. The orientation of the line segments on the page is not important, but the number of line segments connected to each point is important. 

If the bond valence b calculated from (13.4.1) and (13.4.2) for a cluster M matches the number of connecting lines drawn between pairs of adjacent atoms in a conventional valence bond structural formula, the cluster is termed electron-precise. ... 

Constitutional formulae were designed "on paper", primarily to be "in harmony" with known chemical properties and without pretension to "represent the symmetrical or spatial arrangement of the atom in a compound" [22], Not only was this stipulation gradually relaxed to represent three-dimensional structures, but the connecting lines were also soon after assumed to represent definite electronic links between atoms. This assumption opened the door for the introduction of semi-empirical quantum-mechanical characterization of chemical bonds. It is important to realize that chemical bonds have never been observed in any experiment and that they only exist as conjectures to interpret primitive molecular graphs. Their value as heuristic aids in the study of chemical change and composition is beyond dispute, but as a basis for the theoretical understanding of chemical cohesion they are of little value. 

Reminder Simple chemical structures can often be represented by a line formula or by the systematic name of the compound, but complex chemical structures depend on structural representations exhibiting the atom-atom connectivity, including the order and stereochemistry of the bonds. 

A structural formula gives partial or complete information about the way in which the atoms in a molecule are connected and arranged in space. In simple cases, a line formula that is just a sequence of atomic symbols gives structural information provided the reader knows that the formula represents the order of the atoms in the linear structure. 

Figure 5.2. A contour plot for the same region of the 2D COSY spectrum of thebaine as shown in Figure 5.1. This spectrum allows interconnections to be established between all groups of coupled signals (see partial formula), for example a (9-H) to d(10 cc-H), b(Wp-H) to d(lOa-H), d to a and b c(axial 16-H) to g(equatorial 15-H),f(axial 15-H) and e(equatorial 16-H). Connecting lines are drawn to show this last set. Resonances d and e overlap.

Structural formulas serve a key role as devices to facilitate communication of chemical information, but it is important to recognize at the outset that the relationship of a structural formula to molecular structure is a symbolic one. The current system of structural formulas arose largely as a result of chemistry done in the last half of the nineteenth century. Elemental analyses, interrelation of various compounds, and systematic investigation of the reactivity of various functional groups permitted organic chemists to deduce correctly much information about molecular structure. For many molecules, it became possible to draw conclusions as to which atoms were directly connected. Lines drawn between atoms were used to represent direct connections or bonds. These structural deductions predated modern concepts of atomic and molecular structure and of the nature of the forces that bind atoms. With the advent of quantum mechanics and new experimental techniques for accurate determination of such basic structural parameters as bond lengths and bond... 

The most common type of structural formula used by organic chemists, and the fastest to draw, is the bond-line formula. (Some chemists call these skeletal formulas.) The formula in Fig. 1.3 is a bond-line formula for propyl alcohol. The sooner you master the use of bond-line formulas, the more quickly you will be able to draw molecules when you take notes and work problems. And, lacking all of the symbols that are explicitly shown in dash and condensed structural formulas, bond-line formulas allow you to more quickly interpret molecular connectivity and compare one molecular formula with another. 

A structural formula shows the relative placement and connections of atoms in the molecule. It uses symbols for the atoms and either a pair of dots (electron-dot formula) or a line (bond-line formula) to show the elec-H-O-H tron pairs in bonds between the atoms. In water, each H atom is bonded to the O atom, but not to the other H atom. 

BRCT = Beilstein Registry Connection Table BRN = Beilstein Registry Number CAS = Chemical Abstracts Service CNOC = Commission on the Nomenclature of Organic Chemistry CT = connection table ICRS = Index Chemicus Registry System ISI = Institute for Scientific Information RN = CAS Registry Number SCN = Structure Code Number SSSR = smallest set of smallest rings WLN = Wiswesser Line-formula Notation. 

SMILES (simplified molecular-input line-entry specification) a way of specifying a molecular formula and connectivity, but not the three-dimensional geometry... 

A power system is connected to a number of power supply machines that determine the fault level of that. system (e.g. generators and transformers). The impedances of all such equipment and the impedances of the interconnecting cables and overhead lines etc. are the parameters that limit the fault level of the system. For ease of calculation, when determining the fault level of such a system it is essential to consider any one major component as the base and convert the relevant parameters of the other equipment to that base, for a quicker calculation, to establish the required fault level. Below we provide a few common formulae for the calculation of faults on a p.u. basis. For more details refer to a textbook in the references. 

Reihen-anordmmg, /. (Elec.) series connection, -bilder, n.pl. pictures in a series, apecif. motion pictures, -fertigung, /. assembly-line production, -folge, /. sequence, order, succession. -formel,/. series formula, -nummer, /. serial number, -schaltung, /. (Elec.) connection in series. 

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