Proton generalized scheme

As indicated in the general scheme below, butatrienes are the first products from base-induced 1,4-elinination of hydrogen and a suitable leaving group. The butatriene in general very readily undergoes isomerization into enynes, if sufficiently "acidic" protons are available (see Chapter 11 in Ref. 3a). In aprotic media cumulenic ethers are fixed as their lithio derivatives if an excess of alkyllithium is applied... 

How to Construct Proton- and Ion-Sensitive Analytical Probes Principles and General Scheme of Use... 

Fig. 3.1. General scheme for chemical hydrolysis of carboxylic acid esters and amides. Pathway a Proton (general acid) catalyzed hydrolysis. Pathway b HO (general base) catalyzed...

Protons are in general indispensable for the dismutation of superoxide (Eq. (4)). Also in the case of its dismutation catalyzed by a metal center, two protons are needed for the dissociation of the product (H2O2) from the metal center (Scheme 9). Therefore, a complex which can accept two protons upon reduction and release them upon oxidation is an excellent candidate for SOD activity. The studies on proton-coupled electron transfer in Fe- and Mn-SODs 48), demonstrated that the active site of MnSOD consists of more than one proton acceptor (Scheme 10). Since the assignment of species involved in proton transfer is extremely difficult in the case of enzymatic systems, relevant investigations on adequate model complexes could be of vast importance. H2dapsox coordinates to Fe(II) in its neutral form, whereas in the case of Fe(III) it coordinates in the dapsox form. Thus, oxidation and reduction of its iron complex is a proton-coupled electron transfer process 46), which as an energetically favorable... 

The methylcarbamate insecticides are particularly suitable to derivatization owing to the availability of the replaceable proton on the methylcarbamyl nitrogen atom. The proton may be replaced by a wide variety of groups to give reasonably stable products, as indicated by the general scheme below... 

General considerations on the mechanism of C3Hg reaction over HZSM-5 and Ga- HZSH-5. The products obtained from the reaction of C2 C5 alkanes over H-ZSM-5 zeolites were nicely interpreted (3-6) according to the classical carbenlum ion theory and the non-classical theory developed for reactions occurring in superacid media where an alkane is protonated to form the carbocation species. The general scheme proposed for propane reaction over H-ZSM-5 is ... 

In the ionic mechanism, H2 is added up to the substrate as the sum of one H+ and one H in separated steps (53,54). A key feature of this reaction mechanism is that the insertion step of the substrate into the M-H bond is not needed. This mechanism takes place with the general scheme shown in Scheme 11. The first step of the ionic mechanism involves a proton transfer generating a neutral metallic intermediate. In the next step there is a hydride transfer giving rise to the hydrogenated product. 

A general scheme showing how electron transport can result in proton translocation. A, B, D, and E are electron carriers that bind protons when they are reduced. A and D undergo reduction to AH2 and DH2 on the matrix side of the membrane, picking up protons from the solution on this side. They then transfer protons along with electrons to B and E. BH2 and EII are reoxidized on the opposite side of the membrane, releasing protons here. Electrons move without protons from BH2 to D. 

The possible mechanistic pathways can be shown using horizontal changes for electron transfer and vertical ones for proton transfer (Scheme 1). This scheme has been generalized and truncated to show only the reduction of A to AH2. Pyridine reduction would be extended from this scheme to reflect the six electrons and six protons involved. Of course, protonated monocationic species would probably be important only in acidic electrolytes, whereas dianions would normally be formed only in aprotic electrolytes at high junction potentials. The dication, AH22+ is an unlikely species when A is pyridine. 

The difficulty of fitting NH3 into a general scheme of acids and bases was solved in 1923 by Johannes Bronsted and Thomas Lowry, who defined an acid as a proton donor and... 

Scheme J (A) General scheme of HD-exchange in structure S. The D and H in brackets refers to the deuterated and protonated species, respectively. (B) A simplified folding scheme with unfolded (U), folded (N for native) and one intermediate (I) state with H-D exchange considered. Adapted from Ref. 89.

Spectra are usually recorded with complete decoupling of protons by broadband noise decoupling. The general scheme of the sequence for a routine spectrum is illustrated in Fig. 5.4.5a and a set of recording values are listed in Table 5.4.2. 

As discussed above, monomer molecules are capable of functioning either as it-electron donors and n-electron acceptors (e.g. C=C double bond containing compounds), respectively, or as n-electron donors (e.g. epoxides). Therefore, their ground or excited states can interact with donor or acceptor molecules, which are unable to polymerize. For that interaction the general Scheme 3 holds, too. Clearly, in these cases only a homopolymerization of the monomer used takes place. The mechanism of that reaction depends on the electronic properties existing (e.g. monomer acts as donor or acceptor), and on the structural conditions in both molecules. Again, in some cases a proton transfer reaction could occur. 

There are two cases where the general base catalysis observed for an azo coupling reaction is not due to a rate-limiting proton transfer from the cr-complex (51) but to deprotonations of the coupling component when the species which enters the substitution is formed. These reactions follow the general scheme (56-58). 

Cationic polymerization is one of the most fundamental methods for synthesizing polymers.A general scheme for the cationic polymerization of vinyl monomers having a cation stabilizing group (R) is shown in Scheme 9.4. In general, proton acids or carbocations generated from their precursors by acid-promoted ionization reactions are used as... 

Figure 6.1. The four general schemes to produce 2D heteronuclear shift correlation spectra. The relative sensitivities of these approaches are compared for proton correlation experiments with phosphorus-31, carbon-13, and nitrogen-15.

The difference of reactivity between neutral and acidic solvents could only lie in the fact that the aromatic sulphonyl chloride is protonated and consequently reduced more easily in its protonated form. A potential shift of about 0.5 V for the main reduction step (Figure 10b) can be observed in the voltammetries. The general Scheme 951 fits the two possible routes according to the acidity of the medium. 

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