Amino nitrogen resonance

All other resonances of 3 AMP are shifted downfleld during protonation of N1 (Fig.3). It seems that the aromatic character of the adenine ring Increases, which Induces a deshleldlng of all nitrogen atoms except N1. In addition, the rather strong downfleld shift of the amino nitrogen resonance Indicates that a partial double-bond character of the C6-NH2 bond also Increases when a proton Is bound to N1. 

The amino nitrogens of N-nitroso compounds are deshielded substantially more than those of electronically analogous amides, and well separated resonances frequently can be detected65, where geometrical isomerism is possible. 

Using the data of Wilson and Cannan (18), Cleaves (81) was able to show that the rate of formation of pyrrolidone carboxylic acid from glutamic acid in aqueous solution depends directly on the concentration of the ionic species of glutamic acid in solution. Thus, the reactive species are (I), (II), and (IV), while (III) is relatively unreactive. Protonation of the amino group and dissociation of the y-carboxyl group thus makes these groups less reactive carboxylate ion resonance apparently hinders nucleophilic attack by the amino nitrogen. 

Preston, C. M., Rauthan, B. S., Rodger, C., and Ripmeester, J. A. (1982). A hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of p-benzoquinone polymers incorporating amino nitrogen compounds ( synthetic humic acid ). Soil Sci. 134,277-293. 

Proton loss. The side-chain anions from 2- and 4-aminopyridines are stabilized by resonance 761. Aminoazines are thus weak acids their anions react with electrophilic reagents preferentially at the amino nitrogen. 2-Aminopyridine 745 is thus converted by NaNH2/MeI to the 2-methylamino- 763 or 2-dimethylamino-derivatives 764. With EtONO/NaOEt, a sodium diazotate 762 is formed which will couple with phenols. 

Intermediate 3-33 reacts by a route completely analogous to the previous steps to give 3-35, a tautomer of the product. That is, the proton removed from the amino nitrogen of 3-33 leads to a resonance-stabilized anion, 3-34. (The anion formed by removal of a proton from the imide nitrogen would not be resonance stabilized.) The nucleophilic anion, 3-34, adds to the remaining ester carbonyl. Elimination of ethoxide then gives 3-35. 

Figure 3. Phi (p) and Psi ( /) torsional angles. Free rotation can occur around the bonds between the a-carbon of an amino acid and the carbonyl carbon (ly), and between the a-carbon and the nitrogen ((()). Resonance with the carbonyl group makes the peptide bond planar.

Moreland and Hill attribute the weaker inhibiting effect of polycyclic ureas to their higher lipophilicity, their less favourable special configuration, and to the absence of resonance interaction between the ring system and the amino nitrogen. 

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