Basic nitrogen

Unlike the products of condensation of 1,2-diaminoethane and 1-amino-2-hydroxyethane with aminobutynones, which exist almost exclusively in the enole form, benzoxazoles 359,361 and benzothiazoles 360,362 are present in the solution as a tautomeric mixture of the ketone (359, 360) and enole (361,362) forms. This seems to be related to weakening of the imine nitrogen basicity due to adjacent oxygen and sulfur atoms. 

Table 2) as taken from CO-stretching frequencies, vqq (measured in the presence of excess L 0.12-0.13 M solutions of L in CHBr3 Perkin-Elmer 521 (90)] and compared with the nitrogen basicities of the corresponding porphyrins or ligands... 

Also, due to the stronger d -donor ability of Ru11 and Os11, equilibrium (2) can be set up for M = Ru, Os and L = EtOH. The dicarbonyls, e.g. Ru(CO)2(OEP) (97) and Os(CO)2(OEP) (78, 79), can be isolated, but one of the CO molecules is easily displaced, e.g. by H20, and the dynamic tram effect is still operative. Qualitatively, the stability of these dicarbonyls increases with the decrease of the 7r-acceptor capacity (or with the increase of the nitrogen basicity) of the attached porphyrin ligand, as expected from the porphyrin cis effect which is documented in an appropriate variation of the CO-stretching frequencies (see Sect. 7.2, Table 15). 

There remain in this Section to be considered p-aminobenzyl-ideneaniline and />-aminoazobenzene and their derivatives. In these molecules two nitrogen basic centres are conjugated through a benzene ring, and the two systems are isoconjugate. 

Another heteroatom in the feed which affects performance and product quality is nitrogen. Basic nitrogen in the feed tends to lower cracking activity by adsorbing onto the acid sites of the surface of the cracking catalyst. The work of Wu and Schaffer (5), showed that not all nitrogen compounds were equally harmful. They... 

These are related to the relative ring nitrogen basicities ... 

With the exception of semi-empirical models, all models provide very good descriptions of relative nitrogen basicities. Even STO-3G performs acceptably compounds are properly ordered and individual errors rarely exceed 1 -2 kcal/mol. One unexpected result is that neither Hartree-Fock nor any of the density functional models improve on moving from the 6-3IG to the 6-311+G basis set (local density models are an exception). Some individual comparisons improve, but mean absolute errors increase significantly. The reason is unclear. The best overall description is provided by MP2 models. Unlike bond separation energy comparisons (see Table 6-11), these show little sensitivity to underlying basis set and results from the MP2/6-3IG model are as good as those from the MP2/6-311+G model. 

Aminothiazole and its 4-methyl derivative react with the superelectrophilic 4,6-dinitrobenzofuroxan at C(5) to form, for example, (1) in spite of them exhibiting higher nitrogen basicity than aniline.7 In the case of 4,5-dimethyl-2-aminothiazole, however, attack did occur at nitrogen. 

From the reasoning above one could also expect the occurrence of alkyl derivatives of vinylamine which have very similar carbon and nitrogen basicities. 

TABLE 1. Carbon versus nitrogen basicity of enamines10... 

TABLE 3. Nitrogen basicities of some /i-cyano enamines (H20, 30 °C)20... 

A critical reader would perhaps note that the proton affinities of the individual amino acids are not directly relevant to peptides, since the basic amino groups of amino acid are incorporated in amide bonds, for which the nitrogen basicity is far lower. For whole peptides or proteins, even more basic sites are found at the termini of side chains, as in the cases of lysine, histidine and arginine. However, as we will see below, the basicity of the free amino group created during peptide bond dissociation is crucial in determining which of the two dissociation products that will end up with the transferable proton, and thereby the charge. 

Round-bottom flask (250 mL) with septum port syringe 5 mL D2O (99-1- percent) calcium carbide (3 g) D2O trap and 1-L storage flask with stopcocks two Dewars Dry Ice/isopropanol slurry liquid nitrogen basic alumina (optional). 

Since the first structure determination of tri(silyl)amine, which has shown the molecule to have a planar configuration at nitrogen [21], the unexpected structural features of silylated amines have attracted considerable interest. The planar structure is associated with a low nitrogen basicity and with poor donor properties of the silylated amines. Pertinent conclusions had to be drawn from rather limited structural... 

A group of very interesting naturally occurring compounds are known which are nitrogenous basic substances and which are related to uric acid. They are ... 

Intramolecular cyclizations are not restricted to attack by a nucleophilic nitrogen (basic amino or acidic amido group). They can also be catalyzed by a nucleophilic oxygen as found in a carboxylate, phenolic, or alcoholic group. Illustration of the catalytic role of a carboxylate group can be found in hemiester prodrugs of phenol (taken as model compound) or paracetamol (Fig. 6 R = H or NHCOCH3, respectively). In addition to enzymatic hydrolysis, three mechanisms of chemical hydrolysis were seen, namely, acid-catalyzed, base-catalyzed, and an intramolecular nucleophilic attack. 

Phosphazene bases represent a class of non-ionic materials which exhibit exceptionally high degrees of basicity, this being dependent upon the structural composition of the molecules [1, 2]. The core structural unit of non-ionic phosphazene bases is derived from a nitrogen basic center double-bonded to a pentavalent phosphorus (PI unit). This peralkylated triaminoiminophosphorane, through oligomerization, can result in a structurally diverse range of phosphazene bases (Fig. 1). 

Migration to nitrogen, basic media example (in this example, the migration is followed by Nu attack on the heterocumulene. Section 8.9.3, and then decarboxylation. Section 8.9.2) ... 

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