Nitrogen-hydrogen bond forming reaction

Nitrogen - Hydrogen Bond Forming Reaction N-H bond 1... 

Enamines that would formally be derived from ammonium cannot be formed by any process that would expose the product to either acid or base, since the conversion to the imine is exothermic as both the carbon-nitrogen ir-bond (74 kcal mol" 1 cal = 4.18 J) and carbon-hydrogen bond (99 kcal mol" ) are stronger than the carbon-carbon rr-bond (63 kcal mol" ) and nitrogen-hydrogen bond (93 kcal mol" ). However, ethenamine and several substituted analogs have been prepared for spectral analysis (at low temperature) by retro-Diels-Alder reactions (equation 10). ... 

Hydroxylamine hydrochloride (HO-NHa Cl) is a derivative of ammonia. It can react with the carbonyl carbon to form a carbon-nitrogen double bond. The reaction rate is enhanced by acid. This can be readily seen in the reaction mechanism. The proton attaches itself to the carbonyl oxygen rendering a more positive dipole to the carbon, which is now more susceptible to nucleophilic attack by nitrogen. The mechanism is shown below, R can be hydrogen or alkyl group. 

This latter reaction only occurs when there is at least one monodentate phosphine coordinated to the metal. For the purpose of discussion, the remainder of this section will be divided into reactions that (i) form nitrogen-carbon bonds (ii) form nitrogen-hydrogen bonds and (iii) reactions of polynuclear complexes. 

X-ray crystallographic studies of serine protease complexes with transition-state analogs have shown how chymotrypsin stabilizes the tetrahedral oxyanion transition states (structures (c) and (g) in Figure 16.24) of the protease reaction. The amide nitrogens of Ser and Gly form an oxyanion hole in which the substrate carbonyl oxygen is hydrogen-bonded to the amide N-H groups. 

The reaction of 2,4,6-tribromopyridine with phenoxide ion illustrates, in our opinion, the effect of hydrogen bonding as discussed in Section II, B, 3. Reaction (150°, 24 hr) in water gave approximately equal amounts (18% yields) of 2- and 4-monosubstitution, but in phenol under the same conditions only the 2-phenoxy derivative (in high yield plus a small amount of the 2,6-diphenoxy compound) was formed. In water, reaction at the adjacent 2- and 6-position is hindered by the hydrogen bonding (cf. 61) of the solvent to the azine-nitrogen, compared to reaction at the 4-position. On the other hand, in... 

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