Carbon atomic symbol

To insert non-carbon atomic symbols, the user depresses the stylus on the desired atom at the bottom of the display. The tracking cursor disappears and is replaced by a copy of the selected atomic symbol. This can then be moved into position in the developing molecule by depressing the pen at the appropriate position, causing a new atom to be created or a previously existing atom to be converted to the new atom type. Attached bonds are automatically shifted back slightly to make room for the new atom symbol. 

Figure 5.13 shows the way in which the molecules are visualised, their chemical symbol, and the names of the first three members of the series. The carbon atom has four bonds that can join with either one or more carbon atoms (a unique-property) or with atoms of other elements, such as hydrogen. Hydrogen has only one bond, and can therefore join with only one other atom. 

The ROSDAL syntax is characterized by a simple coding of a chemical structure using alphanumeric symbols which can easily be learned by a chemist [14]. In the linear structure representation, each atom of the structure is arbitrarily assigned a unique number, except for the hydrogen atoms. Carbon atoms are shown in the notation only by digits. The other types of atoms carry, in addition, their atomic symbol. In order to describe the bonds between atoms, bond symbols are inserted between the atom numbers. Branches are marked and separated from the other parts of the code by commas [15, 16] (Figure 2-9). The ROSDAL linear notation is rmambiguous but not unique. 

Usually only the indices of the carbon atoms are written, not the symbols hydrogen atoms can have, but do not need, an atom number... 

Another scheme for estimating thermocheraical data, introduced by Allen [12], accumulated the deviations from simple bond additivity in the carbon skeleton. To achieve this, he introduced, over and beyond a contribution from a C-C and a C-H bond, a contribution G(CCC) every time a consecutive arrangement of three carbon atoms was met, and a contribution D(CCC) whenever three carbon atoms were bonded to a central carbon atom. Table 7-3 shows the substructures, the symbols, and the contributions to the heats of formation and to the heats of atomization. 

We can now assign the four carbon p-orbitals, one to each carbon. For simplicity, we will label them with the subscript corresponding to the number of the carbon atom to which the AO belongs. We will use the symbol p to denote AOs and P for MOs. We can now write the Hiickel matrix as a square matrix involving the AOs as shown in Figure 7-20. 

The ring form can be written in a simpler way, showing the hydrogen atoms attached to carbon atoms by lines only and omitting the symbols for the ring carbons ... 

The valence atomic orbitals which are available to form the orbitals of a CC single bond, directed along the x axis, are the 2s and 2px atomic orbitals on each carbon atom. Their admixture—in proportions which depend on the number of neighbors at each carbon and on the subsequent hybridization—creates two (s, p ) hybrids on each atom. One of these hybrids points away from the other atom and can be used for bonding to additional atoms. The pair of hybrids which point at each other overlap and interact in the conventional fashion [we symbolize the non-interacting orbitals by an interruption of the bond axis (Fig. 1)]. The two bond orbitals which are formed in this manner both have [Pg.3]

If the pair of carbon atoms shown above each have only two neighbors so that they are doubly-bonded in the conventional sense, there is an extra p orbital available on each atom. These p orbitals point along the (z) direction, perpendicular to the plane of the molecular fragment. The interaction of these two atomic orbitals via overlap creates a new pair of bond orbitals with local tt symmetry (Fig. 2, where again we have symbolized the non-interacting or-... 

Organic chemists have found a way to draw complex molecular structures in a very simple way, by not showing the C and H atoms explicitly. A line structure represents a chain of carbon atoms by a zigzag line, where each short line indicates a bond and the end of each line represents a carbon atom. Atoms other than C and H are shown by their symbols. Double bonds are represented by a double line and triple bonds by a triple line. Because carbon almost always forms four bonds in organic compounds, there is no need to show the C—FI bonds explicitly. We just fill in the correct number of hydrogen atoms mentally compare the line structure of 2-chlorobutane, QT3C1TC1CF12C]T3 (3a), with its structural form (3b). Line... 

A biradical is a molecule with two unpaired electrons. The unpaired electrons are usually on different atoms, as depicted in (20). In that biradical, one unpaired electron is on one carbon atom of the chain and the second is on another carbon atom several bonds away. In some cases, though, both electrons are on the same atom. One of the most important examples is the oxygen atom itself. Its electron configuration is He]2s22/ x.22py12pzl and its Lewis symbol is -O. The O atom has two unpaired electrons, and so it can be regarded as a special type of biradical. 

As examples we may discuss CO, CN, Nj and NO. CO might be composed of normal or excited atoms, or even of ions. A neutral oxygen atom can form only two bonds. Hence a normal carbon atom, 3P, which can also form two bonds, is at no disadvantage. We can write the following reaction, using symbols similar to those of Lennard-Jones29 and Dunkel,30 whose treatments of the electronic structure of simple molecules have several points of similarity with ours... 

Here symbols in parentheses represent unshared electrons attached to C and O, respectively, and those in braces represent shared electrons. An excited carbon atom 6S lies about 1.6 v. e. above the normal state, but can still form only a double bond with oxygen, so that the resultant molecule should be excited. We write... 

The anomeric symbol a or p, followed by a hyphen, is placed immediately before the configurational symbol D or L of the trivial name or of the configurational prefix denoting the group of chiral carbon atoms that includes the anomeric reference atom. 

Note. In carbohydrate nomenclature, substitution at a heteroatom is normally indicated by citing the locant of the attached carbon atom, followed by a hyphen, and then the italicized heteroatom element symbol, e.g. 2-0-methyl, 5-N-acetyl. Substituents on the same kind of heteroatom are grouped (e.g. 2,3,4-tri-0-methy 1), and substituents of the same kind are cited in alphabetical order of heteroatoms (e.g. 5-N-acetyl-4,8,9-tri-0-acetyl). The alternative format with superscript numerical locants (e.g, N5,(/,(), ( -tetraacetyl), used in some other areas of natural product chemistry, is unusual in carbohydrate names. 

Note 2. In the last four examples, new asymmetric centres have been introduced at the carbonyl carbon atom of the aldehyde or ketone that has reacted with the saccharide. When known, the stereochemistry at such a new centre is indicated by use of the appropriate R or S symbol ([13], Section E) placed in parentheses, immediately before the locants of the relevant prefix. 

Different fields within chemistry have developed their own specialist forms of symbolism. Organic chemistry uses a range of symbols in representations that learners need to make sense of For example, minimal structural representation in organic chemistry (where stractiues may be extensive) uses a formalism that a fine represents two carbon atomic centres joined by a single covalent bond, and saturated with hydrogen except where shown otherwise. 

As the name implies, an amino acid is a bifunctional molecule with a carboxylic acid group at one end and an amine group at the other. All proteins are polyamides made from condensation reactions of amino acids. Every amino acid in proteins has a central carbon atom bonded to one hydrogen atom and to a second group, symbolized in Figure 13-31 as R. 

The number of protons in the nucleus determines the chemical properties of the element. That number is called the atomic number of the element. Each element has a different atomic number. An element may be identified by giving its name or its atomic number. Atomic numbers may be specified by use of a subscript before the symbol of the element. For example, carbon may be designated 6C. The subscript is really unnecessary, since all carbon atoms have atomic number 6, but it is sometimes useful to include it. Atomic numbers are listed in the periodic table and in Table 3-1. 

For even more convenience in representing the structures of organic compounds, particularly in printed material, line formulas are used, so-called because they are printed on one line. In line formulas, each carbon atom is written on a line adjacent to the symbols for the other elements to which it is bonded. Line formulas show the general sequence in which the carbon atoms are attached, but in order to interpret them properly, the permitted total bond orders of all the respective atoms must be kept in mind. Again referring to the compounds (a) to (e) described above, the line formulas are as follows ... 

Carbon, chemical symbol C, has six protons and six electrons. Two electrons fill the inner K energy shell, and there are four electrons in its outer L shell. Since this is exactly halfway to the number eight, which would fill the outer shell, carbon has little tendency to gain or lose electrons. Instead, carbon usually combines by sharing electrons with two, three, or four other atoms. 

Since each line connecting two chemical symbols represents 2 electrons being shared in a bond, we can see that each carbon atom seems to share 4 pairs of electrons with its neighbors. An oxygen atom seems to share 2 pairs of electrons and a hydrogen atom only shares 1 pair of electrons with its neighbor. 

Applying it to glucose, whose absolute configuration has been determined, the molecule is represented as follows with the symbols R and S specified at various asymmetric carbon atoms. 

As seen in the above structures, carbon atoms with exocyclic C=W bonds (where W symbolizes an electron-withdrawing group such as O, NR, or S) count as Z-type atoms. Indeed, 4//-pyrone 56 and tropone 57 (Scheme 27) may be considered to be normal... 

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