Amines protonation

Section 22 19 The N—H stretching frequency of primary and secondary amines appears m the infrared m the 3000-3500 cm region In the NMR spectra of amines protons and carbons of the type H—C—N are more shielded than H—C—O... 

The chemical shift of the amine nitrogen is 55 ppm and shows a clear 3-bond correlation to the aromatic proton giving a fine doublet at 7.49 ppm. There is also a strong, and in this case, very useful, 1-bond correlation to this nitrogen from the amine proton itself. Note that whether or not you see 1-bond correlations depends largely on how broad the -NH signal is in the proton domain. The sharper the -NH, the more likely you are to see them. As with 13C HMBC, 2-bond correlations can sometimes be quite weak and that is so in this case as there is no obvious correlation to be seen from the methylene protons adjacent to the amine. 

Eiden, L. E., Schafer, M. K.-H., Weihe, E. and Schiitz, B. The vesicular amine transporter family (SLC18) amine/proton antiporters required for vesicular accumulation and regulated exocytotic secretion of monoamines and acetylcholine. Eur. J. Physiol. 447 636-640, 2004. 

The sorption processes for cobalt complexes can be complicated by hydrolysis reactions of the complex in solution, surface induced ligand loss processes, sorption of hydrolysis products of either amine, protonated amine, or mixed amine/aquo cobalt complexes, and oxidation/reduction processes associated with cobalt. The principal objective of the XPS studies was to evaluate, the chemical state of cobalt and amine ligands, the surface concentration of the respective elements, and the ligand to cobalt ratio as indicated by the surface nitrogen to cobalt atomic ratio. 

Aniline may complex (as a proton donor) not only with tertiary amines (proton acceptors) such as 7V,7V-dimethylaniline, pyridine or A,A-diethylcyclohexylamine, but also with apparently neutral molecules such as CCI492, benzene93 or chloroform, which acts as proton donor toward amines94. 

A regioselective deprotonation with amide base by preferential abstraction of the a-methylene hydrogen syn to the phenylaziridyl moiety in 116 and subsequent decomposition of the resulting monoanion furnishes, with extrusion of styrene and nitrogen, the alkyllithium 118. After abstraction of the amine proton, the c -alkene 117 is formed with regeneration of the lithium amide base for further use in the catalytic cycle. 

When a molecule contains several potential acidic and/or basic sites, as do those treated in this chapter, the relative /s,mm can help to rank them and also to clarify possible ambiguities. For example, hydroxylamine, H2N—OH, has a reported pK of 5.94 . Does this correspond to the loss of the hydroxyl proton, or an amine proton Or is it telling us that the nitrogen, or the oxygen, has pA"b = 14.00 — 5.94 = 8.06 ... 

The orientation of lone electron pairs at heteroatoms can affect H and 13C chemical shifts substantially. This has been studied in conformationally rigid cyclic amines. Protons in piperidines are shielded significantly if they are antiperiplanar to the nitrogen lone pair70-72. 

Ellipsoidal cryptands can also be synthesized by direct alkylation procedures <77AG(E)720,80CB1487), obviating the need for a diborane or lithium aluminum hydride reduction step. In the case of [l.l.l]cryptand (15a) yields of the final amine alkylation step are enhanced by the amine proton itself acting as a template (81CC777). 

Fig. 15. Conceptualization of processes leading to amine protonation and gel swelling at swelling front. Initially proton attached to carrier diffuses from outer solution (I) to vicinity of front (II). Transfer of proton to amine occurs when amine is still in unhydrated region (III) this represents a transition state. Upon protonation the amine moves into hydrated portion of gel (IV). Plotted is the free energy G at different stages. Activation free energy is AG. This figure illustrates case where proton is attached to a monoacidic buffer. Proton can also be in form of hydronium ion, with accompanying counterion.

Tanaka and Mika 42) suggest that the higher basicity of amine relative to epoxide makes the formation of an amine-proton donor adduct more likely, and they proposed the following equations as an alternative to Eqs. (3-12) and (3-13). 

The need for the presence of at least one amine proton in the substrate and a wealth of experimental evidence support a mechanism in which the lyate ion (or even the solvent itself) acts as a base to remove a proton from a suitably placed amine group, thereby generating a substitutionally labile amido species. There is strong evidence to support the idea that the mode of activation of this species (at least in the case of the Co111 species) is dissociative, but there is still disagreement as to whether the stoichiometric mechanism is dissociative (Z)) or interchange (7d). The distinction between these mechanisms rests upon the presence or absence of an identifiable five-coordinate intermediate that has lost all memory of its origins. 

Other systems are ambiguous and require a careful consideration of the magnitudes of the derived rate constants before a conclusion can be drawn. An extreme case can be found in the pH dependence of the solvolysis of m-[Co(en)2(H20)Cl]2+.330 The rate is independent of pH in the range 7—9, where the complex is almost entirely in the form of ris-[Co(en)2(OH)Cl]+ and it is usually, and probably correctly, assumed that the pH independent rate constant is that for the uncatalyzed aquation of this species.180 However, consideration ought to be given to the possibility that the observed process is the base catalyzed hydrolysis of the aquo complex in which a primary amine proton is removed. Problems of this sort are discussed in ref. 301, p.84. 

In the absence of pKA data for the individual amine protons in these substitutionally labile complexes it is not possible to evaluate k2 and thereby measure precisely the amount by which deprotonation increases the lability of the complex. Even if such data were available it would be difficult, in complexes containing more than one type of amine proton, to be sure whether the two quantities related to the same proton. In spite of this major drawback it is possible to estimate orders of magnitude. The evidence suggests that in Co111 complexes the amido conjugate base can be between 105 and 1013 times more labile than the amine complex from which it was derived.301 The effect is far less marked in equivalent complexes of Crm, Ru111 and Rh111352-353 and, so far, there... 

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