C-protonation

Hammes-Schiffer, S., Tully, J.C. Proton transfer in solution Molecular dynamics with quantum transitions. J. Chem. Phys. 101 (1994) 4657 667. 

Marrink, S.J., Jahnig, F., Berendsen, H.J.C. Proton transport across transient single-file water pores in a lipid membrane studied by molecular dynamics simulations. Biophys. J. 71 (1996) 632-647. 

Oxidation of a sulfide to a sulfoxide or sulfone is accompanied by a decrease m shield ing of the H—C—S—C proton by about 0 3-0 5 ppm for each oxidation... 

The relative eonfiguration C is derived from the eoupling eonstants of the H NMR speetrum the 11.9 Hz coupling of the phenyl-C//proton [Sh = 3.36) proves its antiperiplanar relationship to the... 

Since the vinyl-C//proton at (<5//= 6.33 shows no additional V////couplings apart from the doublet of doublets splitting (cis and trans coupling), the side-chain is a 1-isoprenyl chain E and not a 1-methylbuta-l,3-dienyl residue F. 

Solutions of unstable enols of simple ketones and aldehydes can also be generated in water by addition of a solution of the enolate to water. The initial protonation takes place on oxygen, generating the enol, which is then ketonized at a rate that depends on the solution pH. The ketonization exhibits both acid and base catalysis. Acid catalysis involves C-protonation with concerted 0-deprotonation. 

In agreement with expectation for a rate-determining proton transfer, the reaction shows general acid catalysis. Base-catalyzed ketonization occurs by C-protonation of the enolate. 

The active acylating agent is presumably the C-protonated enol ester... 

The above assumes that C protonation is not excluded for steric reasons. Thus N protonation takes place with derivatives of dehydroquinuclidine and the alkaloids neostrychnine and trimethylconkurchine (( ). N protonation was also believed to occur in the case of 2-N-hexamethyleneimino-bicyclo[l,2,2]-2-heptene, which was believed to give the nortricyclene derivative (6) on protonation with perchloric acid. Later work, however, showed the salt to be the results of C protonation (15) and to have structure 7. 

Iminium salts are readily available from C protonation of the corresponding enamines (7). Experimentally the procedure is very simple The enamine dissolved in ether or some other solvent is treated with an appropriate acid such as anhydrous hydrogen chloride or 70% perchloric acid. The iminium salt usually separates and is then collected. Protonation at low temperatures... 

In addition to electrophilic attack on the pyrrole ring in indole, there is the possibility for additions to the fused benzene ring. First examine the highest-occupied molecular orbital (HOMO) of indole. Which atoms contribute the most What should be the favored position for electrophilic attack Next, compare the energies of the various protonated forms of indole (C protonated only). These serve as models for adducts formed upon electrophilic addition. Which carbon on the pyrrole ring (C2 or C3) is favored for protonation Is this the same as the preference in pyrrole itself (see Chapter 15, Problem 2)1 If not, try to explain why not. Which of the carbons on the benzene ring is most susceptible to protonation Rationalize your result based on what you know about the reactivity of substituted benzenes toward electrophiles. Are any of the benzene carbons as reactive as the most reactive pyrrole carbon Explain. 

Solution The -OCH3 protons absorb around 3 5 to 4.0 8 because they are on carbon bonded to oxygen. The (CP C- protons absorb near 1.05 because they are typical alkanelike protons. 

Oxidation of the iron occurs at a location out of contact with the oxygen of the air. The surface of the metal acts as an anode in a tiny galvanic cell, with the metal at the outer edge of the drop serving as the cathode, (b) Further oxidation of Fe2+ results in the formation of Fe3+ ions, (c) Protons are removed from H,0 as oxide ions combine with Fe3+ ions to deposit as rust. These protons are recycled, as indicated by the dotted line. 

Another approach to a donor adduct of the methylene phosphenium cation is the addition of a phosphonium cation to the phosphaalkyne. The reaction of the protic cation [HPPhal + lCFaSOa] with CjoHuCP produced a white powder which was identified as the P-phosphonio-substituted phosphaalkene [74]. Alternatively to the elimination reaction the phosphaalkynes were protonated. C-protonation of adamantylphosphaacetylene and ferf-butylphosphaacetylene occurred in superacid media under formation of phosphavinyl cations. From these spirocyclic betaines by reaction of l-Ad-C=P (Ad = adamantyl) withB(OTf)3 a phosphavinyl cation could be detected [75]. 

Figure 43. Probability density of the wavepacket after 30 fs of field-free propagation of the accelerated wavepacket as a function of (a) proton coordinate, (b) N=C bond length, (c) proton momentum, and (d) N=C bond momentum. Taken from Ref. [41].

Gakh, E.G., Dougall, D.K., and Baker, D.C., Proton nuclear magnetic resonance studies of monoacylated anthocyanins from the wild carrot part 1. Inter- and intramolecular interactions in solution, Phytochem. Anal., 9, 28, 1998. 

Fig. 34a-c Proton NMR spectra from the on-flow experiment. FIDs recorded after a 1 min, b 3 min, c 7.5 min... 

Fig.39a-c Silicon-29 and proton spectra of diphenylsilane in C6D6. a INEPT spectrum with complete proton decoupling, b proton-coupled INEPT spectrum ( h 201 Hz) the fine structure is due to coupling with thearomatic protons, c proton spectrum showing 29Si satellites for the SiH protons)... 

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