Amido protonation

Figure 2.10 (a) 2D H- N HETCOR correlation spectrum of fully N-labeled complex [(=SiO)2Ta(=NH) (NHj)] and [=Si- NH2] and comparison with 2D double quantum (b) and triple quantum (c) correlation spectra. An exponential line broadening of 100 Hz was applied to all the proton dimensions before Fourier transform. The dotted gray lines correspond to the resonances of the tantalum NH, NH2 and NH3 protons. The dotted circles underline the absence of auto-correlation peaks for the imido proton in the double quantum spectrum (b), and for the amido proton in the triple quantum, spectrum (c) (from Reference [9]). 

An example of the use of NMR in forensic science is the identification of four 5-ethyl-5-alkyl substituted barbiturates, butobarbitone, pentobarbitone, secbutobarbitone, and amylobarbitone. The proton spectra of all four barbiturates show a very broad signal at around 5 8 ppm to 5 10 ppm which is characteristic of amido protons. The useful region of the spectrum for the differentiation of these barbiturates lies between 5... 

Amino- and amido-functionalized monomers can also be polymerized directly with metal catalysts. Living radical polymerization of 2-(dimethylamino)-ethyl methacrylate (FM-5) was achieved with 1-31 (X = Br)/CuBr/L-29 in dichlorobenzene at 50 °C.314 Its ammonium salt (FM-6) was polymerized from the surface of a cross-linked polystyrene latex with CuBr/ L-l in water at 80 °C to generate hydrophilic shells, although there were no data for polymer molecular weight.248 As described above (section II.C.6), (methacrylamides with at least their amido protons unprotected (FM-7, FM-8, and FM-9) can be polymerized with copper-based systems,117168,217,218 but a further optimization seems to be necessary. 

L. Poppe and H. van Halbeek, Nuclear magnetic resonance of hydroxyl and amido protons of oligosaccharides in aqueous solution. Evidence for a strong intramolecular hydrogen bond in sialic acid residues, J. Am. Chem. Soc., 113 (1991) 363-365. 

The presence of the two amido protons in 3 also provides the opportunity to generate heterobimetallic clusters by reaction with organoalkali reagents. The magnesiated cubane 53 is produced in 69% yield from the reaction of dibutylmagnesium with 3 in hot THF. The reaction of 3 with two equivalents of butyllithium at -78 °C in THF generates 54 in 39% yield. The structure of the solvent-separated ion pair 54 is analogous to that of 41. 

Two-dimensional NMR methods that yield a two-dimensional frequency spectrum have not yet been attempted successfully to study metal interactions with HS, although instances of successful applications of these approaches can be found in the study of metalloproteins (Kingery et al., 2001). Mononuclear ( H) two-dimensional NMR experiments, such as total correlation spectroscopy (TOCSY), can show H- H coupling throughout the complete spin system, and exchange protons can provide information on sites to which metal attach. For example, N-containing units in HS that bind the metal can be identified since the amido protons from these structures will exchange and disappear from the spectrum. 

According to its IR spectrum 193 is a secondary benzamide with at least one hydroxyl but no keto group. The PMR spectrum displayed the presence of five aromatic protons, one amido proton with hindered rotation about the C—N bond, one proton adjacent to a secondary hydroxyl, two hydroxymethyl protons, two A-methyls, three tertiary (7-methyls, one secondary (7-methyl, and a cyclopropyl methylene. 

Kupchan et al. 88a) derived the structure of A-benzoylcycloxo-buxidine-F from the following observations. The UV spectrum showed that 195 is a secondary benzamide having the carbonyl group conjugated with the cyclopropane ring. The IR spectrum revealed its close relationship to A-benzoylcycloxobuxine-F (197) (see p. 50). The PMR spectrum showed the presence of aromatic protons, one amido proton, and other substitution pattern practically identical with that mentioned above 88a). 

In an oi-helix each carbonyl oxygen is hydrogen-bonded to the amido proton on the fourth residue up the helix. Thus, if one includes the hydrogen bond, a loop of 13 atoms is formed, as shown in Figure... 

The amido proton of the backbone linkage 119-120 and Gln-11 both act to increase phosphorus electrophilicity by coordination with phosphate oxygens ... 

NMR hardware and pulse sequences have made it possible to detect and quantify previously unobservable NOEs and long-range heteronuclear coupling constants. A potentially highly useful innovation has been the detection of NOEs involving hydroxyl and amido protons in aqueous solution7 i 2 it seems now that there are more tools than ever with which to experimentally probe the conformation of this challenging class of molecules. 

In contrast to the tantalum compounds considered above, the niobium complexes can exist as conformers of different stability at low temperatures. For example, in the H NMR spectrum of complex 4, the intensity ratio between the signals of the conformers is about 3 1 [ 32 ]. The crystal structures of the bis-amido compound 5 and the methylamido compound 6 all show that the lone pair of the amido ligand lies preferentially in the equatorial binding plane of the cyclopentadienyl and imido ligands, a conformation due to the ir bonding interaction of the lone pair with the niobium centre. If rotation about the Nb-Namido bond becomes slow on the NMR time scale then two conformers will be observed, one with the amido proton oriented toward the cyclopentadienyl ring and one with it oriented away. It is supposed that the major conformer is that with the amido proton oriented toward the cyclopentadienyl ring, which minimizes the steric interactions present [32]. 

Crystallographic data on a penicillin sulfoxide should provide more accurate interatomic distances than the Dreiding models used in the early NMR work. The X-ray data on penicillin V sulfoxide could not be refined to an R factor much better than 20%, but the cloxacillin sulfoxide data clearly show that the amido proton is not pointing directly at the sulfoxide oxygen. The interatomic distances for N— H-"0—S and N---0—S are... 

---