Three Nitrogen Atoms

Triazines, reactions of ring N-atoms with electrophiles 88AHC(43)127. 

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Azacarbocyanines. A cyanine containing three carbon atoms between heterocychc nuclei is called a carbocyanine (n = 1 in (46)). Replacing these carbon atoms by one, two, and three nitrogen atoms produces azacarbocyanines, diazacarbocyanines, and triazacarbocyanines, respectively. Dyes of these three classes are important yellow dyes for polyacrylonitrile, eg. Cl Basic Yellow 28 [52757-89-8J (Cl 48054) (47). 

Diacylhydrazines (32) on heating with a primary amine undergo cyclization to the 1,2,4-triazole derivative (38). It is assumed that the amidrazone (37) is an intermediate in the reaction. Most practical syntheses of 1,2,4-triazoles now utilize an amidrazone or a derivative of this alicyclic intermediate containing three nitrogen atoms, and these variations are discussed in Chapter 4.12. 

Among the azafulvalenes, those possessing three nitrogen atoms in the cross-conjugated system are the smallest group to date.Tliere are a number... 

The following compound contains three nitrogen atoms. Rank them in order of increasing basicity. 

Histamine, whose release in the body triggers nasal secretions and constricted airways, has three nitrogen atoms. List them in order of increasing basicity, and explain your ordering. 

RING SYSTEMS CONTAINING THREE NITROGEN ATOMS... 

The only reported structure of a stannanimine (entry 4, Table V), shown below, was found to have a trigonal-planar arrangement of the three nitrogen atoms about the tin atom.88 The Sn=N double bond is significantly shorter than the two Sn—N single bonds (1.921(2) versus 2.015(2) and 2.030(3) A). 

Na has an oxidation number of +1. Therefore, the total charge on the three nitrogen atoms is -1 and the average charge, which is equal to the oxidation number, is - (Three nitrogen atoms, times - each, have a total of oxidation numbers equal to an integer, — 1.)... 

Among the five-membered heterocycles with three nitrogen atoms, triazoles and benzotriazoles are of significant practical importance. In the case of ben-zotriazole, the aromaticity of the benzenoid 1H-benzotriazole (90A, R = H) has been considered to be greater than that of the quinonoid 2/7-benzotria-zole (90B, R = H) (Scheme 43).134 However, the difference in aromaticity between tautomers is greatly dependent on the dielectric constant of the medium. 

In the deoxygenated form, each Cu(I) centre is coordinated to three nitrogen atoms of three histidines. The great Cu/Cu separation (4.62 A) foreshadows the presence of a cavity able to host a dioxygen molecule. In fact, in the oxygenated form, the oxygen molecule is planarily positioned according to a p-rj2 r]2 peroxo coordination, and the Cu/Cu separation decreases (—3.5 A). 

The structural features of the linear R-Cu-R arrangement are identical to those observed for other [R2CU] anionic units discussed previously (cf. Fig. 1.31). The [Li2CN(THF)2(PMDTA)2] cationic unit consists of a central cyanide moiety, to which two lithium atoms are bound in end-on fashion. Coordination saturation at each lithium atom is achieved by coordination of the three nitrogen atoms of the PMDTA molecule and one THF molecule, rendering each lithium atom penta-coordinate. Recent H, Li HOESY experiments showed that this ionic structure found in the solid state is probably retained in polar solvents such as THF [140]. 

This may be studied in either direction by adjusting the pH and reactant concentrations. Substantial evidence exists for a mechanism in which three nitrogen atoms of the polyamine bind to the metal (10) before the rds of M-N eleavage, which leads to the final products. See also Refs. 17 and 119. 

In the 6-NH2 deprotonated radical, an unpaired electron can be delocalized over only three nitrogen atoms. These are single nitrogen of the group NH and two nitrogens of the six-membered ring. An unpaired electron can also be delocalized over two carbon atoms (one by one of the six- and five-membered rings). This part of delocalization is depicted in Scheme 1.24. 

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