Nitrogen, Atomic Number

Nitrogen, N, composes 78% by volume of air in the form of diatomic Nj molecules. The atomic mass of nitrogen is 14.0067, and the nuclei of nitrogen atoms contain 7 protons and 7 neutrons. Nitrogen has 5 outer electrons, so its Lewis symbol is 

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Number of nitrogen atoms Number of aromatic atoms Number of rotatable bonds Number of hydrogen bond acceptors Sum of van der Waal surface areas of basic atoms... 

Only one divalent hetero atom can be incorporated into a simple five-membered, aromatic heterocycle. These systems are named with the non-nitrogen atom numbered as 1, and the positions of the nitrogen atoms shown with reference to the divalent atom. 

Figure 6.25 A comparison of mean molecular weight, number of oxygen atoms, number of nitrogen atoms, number of chiral centers, and the ratio of aromatic atoms to total ring atoms for drugs, natural products, and combinatorial chemistry compounds. Note that in some cases median values were significantly different from the mean, resulting in broad property distributions. (Feher, M., Schmidt, J.M. Property distributions Differences between drugs, natural products, and molecules from combinatorial chemistry. J. Chem. Inf. Comput. Sci. 2003, 43, 218-227.)...

Nitrogen, atomic number 7, has 7 electrons, of which 2 are paired in the b orbital, 2 are paired in the 2s orbital, and 3 occupy singly each of the 3 available 2p orbitals. This electron configuration is designated as ls 2s 2p. ... 

We must now consider which functional groups are involved in the assembly of these compounds. In the case of the formation of a nucleoside, the nitrogen atom number 3 of a pyrimidine base or the nitrogen atom number 9 of a purine base becomes linked to the carbon atom number 1 of the pentose sugar, with the elimination of water. According to the conventions of sugar chemistry the carbon atom number 1... 

These may, for convenience, be divided into a number of topics but all are closely related depending very largely on the presence of the lone pair of electrons on the nitrogen atom. 

The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope. 

A great number of monoaza or polyaza. either symmetrica] or unsym-metrical, mono trimethine thiazolocyainines have been synthesized in order to verify or to obtain semiempirical rules, more or less based on the resonance theory, concerning the relation between the color of a thiazolo dye and the number and place of nitrogen atoms in the chromophoric chain. For example. Forster s rule applies to ionic dyes and stipulates that the will increase with the decreasing tendency of chromophoric atoms lying between the two auxochromes to take up the characteristic charges (90). 

Knott s rule concerns the importance of the place of the nitrogen atom replacing a methine carbon in the conjugated chain when the atom is separated from the active auxochromic atoms by an odd number of conjugated atoms, the shift is bathochromic. It is hypsochromic when there is an even number, Tne importance of the shift could establish a measure of M effect of various heterocyclic nuclei (79. 124). Many papers have been published, and examples have been given to verify these rules (79-84). 

First the peak for the molecular ion M for all compounds that contain only car bon hydrogen and oxygen has an m z value that is an even number The presence of a nitrogen atom m the molecule requires that the m z value for the molecular ion be odd An odd number of nitrogens corresponds to an odd value of the molecular weight an even number of nitrogens corresponds to an even molecular weight... 

When a chain or ring system is composed entirely of alternating silicon and oxygen atoms, the parent name siloxane is used with a multiplying affix to denote the number of silicon atoms present. The parent name silazane implies alternating silicon and nitrogen atoms multiplying affixes denote the number of silicon atoms present. 

Chiral Center. The chiral center, which is the chiral element most commonly met, is exemplified by an asymmetric carbon with a tetrahedral arrangement of ligands about the carbon. The ligands comprise four different atoms or groups. One ligand may be a lone pair of electrons another, a phantom atom of atomic number zero. This situation is encountered in sulfoxides or with a nitrogen atom. Lactic acid is an example of a molecule with an asymmetric (chiral) carbon. (See Fig. 1.13b.)... 

For example, if the exact mass is 177.0426 for a compound containing only C, H, O, and N (note the odd mass which indicates an odd number of nitrogen atoms), then... 

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