The Amide Ion, NH

Amide ion formation by the reaction NH3 H NH2 +H2 after electron impact on NH3 is less important than the formation via resonance capture of electrons by NH3 as described 

A very small amount of NH2 was identified among the products of the autocatalytical decomposition of NH3 at a Pt filament at 1500 K. The NHJ concentration seems to increase exponentially with temperature above 1500 K [16]. The possible presence of NH2 besides 0 in the products of C2H2-O2-N2 flames was deduced from a signal in the mass spectrum and from the experimentally observed formation of NH3 [17]. 

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Phosphorus, iodine and sulphm which are all insoluble in water are soluble in liquid ammonia. Sinee the amide ion, NH, is a very strong base, liquid ammonia is a good solvent to obtain a strongly basic medium. 

This topic is discussed in detail in Chapter 9 and only an outline is presented here. When simple aryl halides react with strong bases such as the amide ion, NH,, a hydrogen atom adjacent to the C-halogen unit is abstracted by the base. The resulting carbanion acts as a nucleophile... 

When ammonia acts as an acid, it forms the amide ion NH. ... 

The amide ion (NH is a Brpnsted base. Use Lewis structures to represent the reaction between the amide ion and water. 

Ionization of liquid ammonia and water solutions.—Solutions of certain salts in liquid ammonia are good conductors of electricity so that liquid ammonia approaches water in its ionizing power. The effect, however, is largely due to the high speed at which the ions are supposed to travel in the solvent. For example, E. C. Franklin and H. P. Cady1 find that univalent ions travel, at —33°, nearly three lames as fast as in aq. soln. at 18°. Just as the solvent water, in the ionization theory of hydrolysis, is supposed to be ionized H20=0H -f-H, so in ammonolysis, the solvent ammonia is supposed to be ionized NH3==NH2-j-H . Sodamide, NaNH, furnishes sodium ions Na and amide ions NH 2 when dissolved in liquid ammonia, and it is to be considered as a base. It reddens phenolphthalein. The neutralization of this solution results in the union of H ions with NH2 ions to form ammonia molecules, just as the neutralization of bases is regarded as an effect of the union of H and OH ions. Acetamide, CH3.CO.NH2, ionizes in liquid ammonia in an analogous manner CH3.CO.NH2 CH3.CO.NH -f-H, and it thus behaves as an acid. 

The last three, the NH2, NH , and N ions, are found in the salt-like amides, imides, and nitrides of the most electropositive metals, but with the exception of the amide ion the stereochemistry of nitrogen is based on N with no lone pairs and N with one lone pair. These two states of the nitrogen atom correspond to the classical trivalent and pentavalent states, now preferably regarded as oxidation rather than valence states. 

Substituted 4-chloropyrimidine derivatives 4 can be converted into 2,4-disubstituted 1,3,5-tri-azines 5 in 13 to 83% yield when treated with potassium amide in liquid ammonia at — 33 °C.8"10 The reaction presumably proceeds via initial attack of the amide ion at C6 of the pyrimidine ring and subsequent ring cleavage of the C5-C6 bond, an assumption confirmed by H and l3C NMR spectroscopic studies.11 1,3,5-Triazines are not formed from 4-chloropy-rimidines containing a substituent at position 2 which has a directly attached CH or NH group.9 In these cases, 2-substituted pyrimidin-4-amines are obtained, probably by an addition-elimination mechanism. 

It was concluded that enantioselectivity is controlled by different degrees of iminium ion stabilization via H-bonding interactions between the iminium ion NH proton and both the amide carbonyl group and the thiourea-bound cyanide ion. However, distinct structural features responsible for that more effective stabilization are not easy to specify. The 3D structures of TSIU, TS2U, TSlS, and TS2S can be found in the CD. 

In organic chemistry the term refers to compounds containing the NH2 ion or the > NH group. These are prepared by the action of heat on amides or by metathetica reactions in liquid ammonia. The heavy metal imides are explosive. 

Inhibitors as well as substrates bind in this crevice between the domains. From the numerous studies of different inhibitors bound to serine pro-teinases we have chosen as an illustration the binding of a small peptide inhibitor, Ac-Pro-Ala-Pro-Tyr-COOH to a bacterial chymotrypsin (Figure 11.9). The enzyme-peptide complex was formed by adding a large excess of the substrate Ac-Pro-Ala-Pro-Tyr-CO-NHz to crystals of the enzyme. The enzyme molecules within the crystals catalyze cleavage of the terminal amide group to produce the products Ac-Pro-Ala-Pro-Tyr-COOH and NHs. The ammonium ions diffuse away, but the peptide product remains bound as an inhibitor to the active site of the enzyme. 

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