N-H protons

The chemical shifts of O—H and N—H protons are temperature and concentration dependent... 

The chemical shift of the N—H proton of amides appears m the range 8 5-8 It IS often a very broad peak sometimes it is so broad that it does not rise much over the baseline and can be lost m the background noise... 

Reaction of free-base porphyrin compounds with iton(II) salts in an appropriate solvent results in loss of the two N—H protons and insertion of iron into the tetradentate porphyrin dianion ligand. Five-coordinate iton(III) porphyrin complexes (hemins), which usually have the anion of the iton(II) salt for the fifth or axial ligand, ate isolated if the reaction is carried out in the presence of air. Iron(II) porphyrin complexes (hemes) can be isolated if the reaction and workup is conducted under rigorously anaerobic conditions. Typically, however, iton(II) complexes are obtained from iton(III) porphyrin complexes by reduction with dithionite, thiolate, borohydtide, chromous ion, or other reducing agents. 

Nuclear Magnetic Resonance. The nmr spectmm of aromatic amines shows resonance attributable to the N—H protons and the protons of any A/-alkyl substituents that are present. The N—H protons usually absorb in the 5 3.6—4.7 range. The position of the resonance peak varies with the concentration of the amine and the nature of the solvent employed. In aromatic amines, the resonance associated with N—CH protons occurs near 5 3.0, somewhat further downfield than those in the aliphatic amines. 

The n + 1 mle should be amended to read When a proton coupled to H , Hj, etc., and J b Jac Jad etc., the original signal for H, is split into n + 1 peaks by n H , protons, each of these lines is further split into n + 1 peaks by n protons, and each of these into n + 1 lines by n protons, and so on. Bear in mind that because of overlapping peaks, the number of lines actually observed can be less than that expected on the basis of the splitting rule. 

Base abstracts a weakly acidic N-H proton, yielding a hydrazone anion. This anion has a resonance form that places the negative charge on carbon and the double bond between nitrogens. 

In addition to their behavior as bases, primary and secondary amines can also act as very weak acids because an N-H proton can be removed by a sufficiently strong base. We ve seen, for example, how diisopropylamine (pK-A 40) reacts with butyilithium to yield lithium diisopropylamide (LDA Section 22.5). Dialkylamine anions like LDA are extremely powerful bases that are often used... 

Abstraction of the remaining N-H proton by base gives a resonance-stabilized bromoamide anion. . . ... 

Although pyrrole is a much weaker base than most other amines, it is a much stronger acid (p/C, 15 tor the pyrrole versus 35 for diethylamine). The N—H proton is readily abstracted by base to yield the pyrrole anion,... 

A histidine deprotonates the acetyl-CoA enol, which adds to the ketone carbonyl group of oxaloacetate in an aldol-like reaction. Simultaneously, an acid N-H proton of another histidine protonates the carbonyl oxygen, producing (S)-citryl CoA. 

In the case of the smaller macrocycle [13]aneN4, six configurational isomers exist for [Ni([13]aneN4)]2+ due to the orientation of the N—H protons above or below the plane of the macrocycle. X-ray crystallography and NMR spectroscopy, respectively, revealed that the R,iS,7 ,iS -[Ni([13]aneN4)]2+ form (trans- ) is the preferred one both in aqueous solution and in the solid state.1 43... 

Almost all the reported compounds have been characterized with the help of various nuclear magnetic resonance (NMR) techniques. For previous studies of the compounds, refer to CHEC-II(1996) <1996CHEC-II(8)713>.The H NMR spectrum (300MHz) of 2,3,7-trirnethyl-3a,9a-dihydro-1,8-dithiaMa,5,9-triazacyclopenta[3]naphthalene-4,6-dione 47 <2000JHC1161> showed the presence of one quartet at 8 4.23 corresponding to the CH. Another broad singlet corresponds to the presence of the N-H proton. 

When treated with DBU at elevated temperature, l-[(benzotriazol-l-yl)methyl -2-aminopyridine salts 741 eliminate rather the N-H proton than the C-H one. Intermediates 742 can be trapped with aromatic aldehydes to create betaines 743. The consecutive cyclocondensation and elimination of benzotriazole results in formation of imidazolo[l,2-rz]pyridines 744 in good yields (Scheme 117) <2000JOC9201>. Aldehydes with enolizable a-protons fail to give bicyclic systems 744, producing corresponding enamines instead. 

Amino groups may act not only as proton acceptor, but also as proton donor. Acidic N—H protons interact with basic solvents. In these cases an ortho-nitro group in an aniline system competes with the solvent by an internal hydrogen bond66, as depicted in 12. The stretching frequencies (by IR spectra in carbon tetrachloride) of vnh of complexes between A-methylaniline or diphenylamine (and some nitro-anilines66) and solvents depend on the proton accepting ability of the solvent (which is a moderate base)67. The frequency shifts are linearly related to the solvent s donor number (DN)3. 

The assignment of the resonances is also shown in Figure 7, in agreement with the proposed structure, including the fraws,fraws-divinylidene conformation. However, the integration of the amine (N—H) protons of the ring was not very accurate due to the rapid... 

Von Runge and Triebs used a solution of dinitrogen pentoxide in chloroform for the N-nitration of both amides and imides. Solutions of dinitrogen pentoxide in chlorinated solvents are not neutral nitrating agents when amides and imides are nitrated - the presence of acidic N-H protons in these substrates leads to the formation of nitric acid. Sodium fluoride acts like a base towards nitric acid and so its addition to these reactions can increase product yield. Sodium acetate has been used for the same purpose during the nitration of n-butyl-V, V -dimethylurea. The effectiveness of dinitrogen pentoxide for the V-nitration of ureas is further illustrated by its use in the conversion of 2-imidazolidinone to N, V -dinitro-2-imidazolidinone in 90 % yield. In the presence of sodium fluoride the yield for this reaction exceeds 90 %. 

The N-H protons of primary and secondary amides are slow to exchange and require heating or base catalysis and this is one way an amide functional group can be distinguished from other functional groups. 

Porphyrins can be lithiated by replacement of the two N—H protons. Dialkali metal salts have been synthesized and characterized by XRD crystallography. The hole-in-the-middle... 

The Shapiro reaction occurs when a tosylhydrazone 86, easily prepared from a ketone and tosylhydrazine, is treated with 2 equivalents of an ethereal solution of n-butyllithium 87, resulting first in the removal of the N—H proton to give the anion 88 and then of a one proton from the less-substituted a position to give the dianion 89. Elimination of lithium p-toluenesulfinate in the rate-limiting step gives the lithium aUtenyldiazenide 90, which suffers loss of nitrogen to afford the alkenyllithium 91 (equation 31) ° . ... 

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