Protonation equation

The cyclopropane cyclizations by elimination of triflinic acid (CF3S02H) are readily effected by basic treatment of triflones (trifluoromethyl alkyl sulfones) with activated /-protons (equations 46 and 47)39. The cyclopropane diesters 45 are formed on treatment of 44 with potassium hydride in DMSO or sodium methoxide in methanol (equation 48). In contrast, the monoester 46 failed to give the desired cyclopropane40. Addition of carbanions derived from /f, y-unsaturated phenyl sulfones to a, /i-unsaturated carboxylic esters and subsequent elimination of benzenesulfinate ion give cyclopropanes possessing the unsaturated side chain and the ester function in trans positions (equation 49)41. 

S-C sMes)Ir1"(L)C1]1 complexes (L = bpy and phen derivatives) form stable hydrides upon oxidative addition of a proton to the doubly reduced [(775-C5Me5)Ir1(L)]° intermediate (Equations (14) and (15)),23 24 26 28 which have been characterized by absorption spectroscopy and H-NMR spectrometry. Additional electrochemical activation is thus required for efficient H2 evolution, by either spontaneous decomposition (Equation (17)) or protonation (Equation (18)) of the reduced hydride complex (ECE mechanism) 24,26,28... 

There are different ways to ionize a molecule (M, Scheme 2.1) extraction of an electron from gas phase molecules (Mg), yielding radical cations [Equation (2.1)], as occurs in electron ionization, or addition of one [Equation (2.2) Cl, MALDI, etc.)] or more protons [Equation (2.3) ESI]. Similarly, molecules can be ionized by the formation of negative ions due to single [Equation (2.4)] or multiple proton abstraction [Equation (2.5)]. 

Alkenes are not acidic enough for their acidities to be measured in terms of the usual solution definition of dissociation into anion and proton (equation 2). 

Imura and Suzuki36 have prepared labelled organotin compounds from artificial tin isotopes produced in a cyclotron. The carrier-free tin-113 radioisotope was produced by irradiating indium-115 oxide with 40-MeV protons (equation 33). 

An ethynylcerium reagent was effectively utilized in the last step for the total synthesis of desogestrel 17.12 Desogestrel was isolated in 92% yield from the corresponding ketone 16, bearing acidic a-protons (Equation (2)). 

The vinyl metal intermediate arising from intermolecular nucleophilic addition of an oxygen nucleophile to a metal-alkyne complex has been harnessed for further transformations prior to protonation. An example is the ruthenium-catalyzed benzannulation of 1,5-enedyines that occurs through a tandem sequence involving hydroalk-oxylation, carbometallation, and protonation (Equation (82)).293... 

Equation (6.27) demonstrated how the concentration of the solvated protons equates to the concentration of a mono-protic acid from which it derived but, from Equation (6.28), the concentration of the solvated protons will be twice the concentration if the parent acid is di-protic. These different stoichiometries affect the pH, as demonstrated now by Worked Examples 6.6 and 6.7. 

By analogy with the basicity towards protons (equation 5) the basicity towards monocharged metal ions (Table 4) is defined by means of the thermodynamics of the reaction ... 

Matsson and coworkers have measured the carbon-1 l/carbon-14 kinetic isotope effects for several Menshutkin reactions (equation 35) in an attempt to model the S/v2 transition state for this important class of organic reaction. These isotope effects are unusual because they are based on the artificially-made radioactive carbon-11 isotope. The radioactive carbon-11 isotope is produced in a cyclotron or linear accelerator by bombarding nitrogen-14 atoms with between 18- and 30-MeV protons (equation 36). 

In solution, certain complexes are observed to undergo an envelope-flip from one face of the diene ligand to the other. The XH NMR spectra of Cp2Zr(s-cis diene) complexes (11 R = R" = H) at ambient temperatures indicate a fluxional process which equilibrates the Cp signals as well as the terminal protons (equation 4). At lower temperature, signals for a... 

Tertiary amides bearing epoxide and other labile moieties can be converted to the corresponding ketones (400a and 400b) in good yields, by treatment with alkyl- or aryllithiums followed by the usual quenching with a proton (equation 108). Furthermore, if the quenching is done with a peracid the amide is transformed to an ester (401, equation 109). Both processes leave the epoxy function unscathed. ... 

A similar type of substitution, which clearly shows the electrophilic character, occurs in vinylidene carbenoids. In an early example of this reaction, Kobrich and AnsarP observed that the aUcene 70 results when the fi-configurated vinyl lithium compound 68 is treated with an excess of butyllithium and the fithioafkene 69 formed thereby is protonated (equation 41). Obviously, the nucleophilic attack of the butyl residue on the carbenoid takes place with inversion of the configuration. 

On the contrary, a-lithiated epoxides have found wide application in syntheses . The existence of this type of intermediate as well as its carbenoid character became obvious from a transannular reaction of cyclooctene oxide 89 observed by Cope and coworkers. Thus, deuterium-labeling studies revealed that the lithiated epoxide 90 is formed upon treatment of the oxirane 89 with bases like lithium diethylamide. Then, a transannular C—H insertion occurs and the bicyclic carbinol 92 forms after protonation (equation 51). This result can be interpreted as a C—H insertion reaction of the lithium carbenoid 90 itself. On the other hand, this transformation could proceed via the a-alkoxy carbene 91. In both cases, the release of strain due to the opening of the oxirane ring is a significant driving force of the reaction. 

A related scheme can be applied to indole synthesis, with the aromatization being the result of elimination of Pd(0) and a proton (equation 27) (76JA2674). This scheme has been put into practice for AT-alkyl-o-allylanilines, a few aryl-substituted analogs and methyl-substituted allyl groups. The requisite o-allylanilines were obtained from o-bromoanilines and allylnickel. Provided the requisite starting materials can be constructed, the mild conditions of this cyclization would seem to recommend it for sensitive molecules. 

The chemistry of the reduction of NAD+ has been solved most elegantly (Chapter 8, section Bi).2 Oxidation of the alcohol involves the removal of two hydrogen atoms. One is transferred directly to the 4 position of the nicotinamide ring of the NAD+, and the other is released as a proton (equation 16.1).3,4 It is generally thought that the hydrogen is transferred as a hydride ion H , but a radical intermediate cannot be ruled out. For convenience, we shall assume that the mechanism is the hydride transfer. 

These are not accessible from coordinated dinitrogen and the preparative routes involve alkylation (equation 172) or protonation (equation 173) of hydrazido(2—) precursors or direct use of the hydrazine with elimination of hydrogen halide (equation 174). 

Heterolytic cleavage. This leads to formation of a metal hydride with release of a proton (equation 1). The formal oxidation state of the metal does not change. This mode of hydrogen activation is common in hydrogenation by complexes of ruthenium(II). 

The acid-catalyzed reactions proceed through a carbocation intermediate formed by protonation of the double bond, followed by nucleophilic attack of HN3 and subsequent loss of a proton (equation 181). 

At pH values near neutral, a pH-independent rate of ketonization is frequently observed, which may be attributed to several different mechanisms (see section Mechanism of the Uncatalyzed Reaction ) carbon protonation of E by water or a concerted transfer of the enol proton to carbon through one or more solvent molecules, and carbon protonation of Ee by the proton, Equation (7). For pH << pAE, the right-hand expression becomes independent of cH . 

When an acidic solution (pH = 3.6) containing 2.5 x 10-s m Ct and 2.0 x 10-2 m Co(CN) - is irradiated at 365 nm, most of the incident light is absorbed by Ct (Figure 23), which undergoes photoisomerization to Cc. Since the pH of the solution is sufficiently acidic, Cc is rapidly protonated (Equation 2), with the consequent appearance of the absorption band with its maximum at 434 nm (Figure 24) and of the emission band characteristic of the AH+ species, with its maximum at 530 nm (Figure 6). 

We calculate the dipolar terms giving more of the detail for the proton (equation (11.62)) we have... 

All the behavior in the pH ranges mentioned so far is attributed to rate-controlling C-protonation (equation 15). Taking A-protonation into account, the rate law for this mechanism is equation 20. The factor involving K H+ represents the fraction of enamine in the free, unprotonated form. The first plateau (alkaline region) and the rise in ks x with decreasing pH occur in pH ranges where K H+ > [H+], hence k/s 1 = h2o + h+[H+]. At the second plateau [H+] K%H+, the enamine is rapidly... 

A further PLP reaction involving enamine chemistry has to do with / -elimination reactions, that probably commences analogously to the well-characterized transamination reaction. Instead of hydrolysis of the Schiff base, these reactions result in proton abstraction, this time at the / rather than the a carbon of the amino acid. The intermediate iminium ion is the electron sink that helps to acidify the / proton (equation 14). 

The photocatalytic Cr(Vl) reduction is more feasible at low pH because the net reaction consumes protons (Equations (18) and (19)), but use of neutral or alkaline conditions can be more convenient because Cr(lll) can be precipitated as the hydroxide and immobilized, avoiding expensive separation steps after the photocatalytic process, an adequate acid or strong basic treatment easily separates Cr(lll) from the catalyst (Lin et al., 1993). 

Finally, a heteroatom-substituted carbene can be converted in a two-step process to an analog lacking the electron-donating substituent by hydride addition and subsequent protonation (equation... 

Rh(CO)(/u.-DPPM)2Mn(CO)3 also forms dimetallated olefin complexes, which can be converted to vinyl derivatives by protonation (equation 30 (R = CF3, C02Me)). 

If production of an oxidizing hole in the da orbital is the important factor in the photochemical reaction, then electrochemical veneration of such a hole should produce a highly reactive intermediate mat would mimic the initial step in the 3(da po) photoreaction. Several of the binuclear complexes undergo reversible one-electron oxidations in noncoordinating solvents (22-24). The complex Rh2(TMB)42+ possesses a quasireversible one-electron oxidation at 0.74 V (Electrochemical measurements for [Rh2(TMB)4](PF6)2 CH2CI2/TBAPF6 (0.1 M), glassy carbon electrode, 25°C, SSCE reference electrode). Electrochemical oxidation of Rh2(TMB)42+ in the presence of 1,4-cyclohexadiene exhibits an enhanced anodic current with loss of the cathodic wave, behavior indicative of an electrocatalytic process (25). Bulk electrolysis of Rh2(TMB)42+ in an excess of 1,4-cyclohexadiene results in the formation of benzene and two protons (Equation 4). 

The main factor which allows observation of the NMR signals is the rather small magnitude of hyperfine couplings involved. Small A values will not greatly affect the transverse relaxation time T2 of the proton [equation (18)] and thus the NMR bandwidth will not be greatly increased. Byers and Williams (56) have studied some dimeric cupric complexes which are models for copper dimer units in proteins. Interest was particularly centred around the possibility that, if appreciable copper(ii) interactions occur, a mechanism for mutual fast relaxation is provided which in turn may lead to much narrower linewidths and measurable paramagnetic shifts. The systems are illustrated in [6]. 

Nelsen et al. have discovered that simple alkyl diazo compounds, which are normally not dienophiles, will react in a Diels-Alder fashion if protonated (equation 67). " It was suggested that protonation facilitates the reaction thermodynamically, since hydrazines are much stronger bases than azo compounds. 

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