Secondary protons

Most aliphatic ketones can lose a proton from either of two carbon atoms adjacent to the carbonyl. The question of which of the possible carbanions or salts is the effective reagent in a given base-catalyzed reaction depends on the nature of the electrophilic reagent with which the ion subsequently reacts. Thus alkyl methyl ketones lose a primary proton in their reactions with alkali and iodine, alkali and an aldehyde, or alkali and carbon dioxide, but lose a secondary proton in certain other reactions. 

The reactions in which the methyl ketone loses a primary proton are all fast reactions, and the direction of the reaction is determined by the fact that an electron-releasing alkyl group slows down the removal of the secondary proton from the methylene group. On the other hand a slow reaction, like the base-catalyzed reaction of ketones with dimethyl sulfate in ether, gives a product corresponding to the removal of a proton from the more alkylated carbon.418... 

The high energy primary cosmic rays produce many secondary neutrons and protons which in turn are responsible for most of the spallation reactions resulting in radionuclide production in the atmosphere. The formation of these radionuclides occurs at reaction thresholds of 10-40 M.e.v. Because of local ionization losses the secondary protons lose their... 

Immonium salts may be secondary protonation products, ammonium salt formation occurring first. Thus, immonium salts of... 

Let us take the case of adjacent carbon atoms carrying, respectively, a pair of secondary protons and a tertiary proton, and consider first the absorption by one of the secondary protons ... 

The magnetic field that a secondary proton feels at a particular instant is slightly increased or slightly decreased by the spin of the neighboring tertiary proton increased if the tertiary proton happens at that instant to be aligned with the applied... 

For half the molecules, then, absorption by a secondary proton is shifted slightly downfield, and for the other half of the molecules the absorption is shifted slightly upheld. The signal is split into two peaks a doublet, with equal peak intensities (Fig. 13.9). 

It is, in its turn, affected by the spin of the neighboring secondary protons. But now there are two protons whose alignments in the applied field we must consider. There are four equally probable combinations of spin alignments for these two protons, of which two are equivalent. At any instant, therefore, the tertiary proton feels any one of three fields, and its signal is split into three equally spaced peaks a triplet, with relative peak intensities 1 2 1, reflecting the combined (double) probability of the two equivalent combinations (Fig. 13.10),... 

Jy Sec. 13.11) in the doublet is exactly the same as the separation of peaks in the triplet. (Spin-spin coupling is a reciprocal affair, and the effect of the secondary protons on the tertiary proton must be identical with the effect of the tertiary proton on the secondary protons.) Even if they were to appear in a complicated spectrum of many absorption peaks, the identical peak separations would tell us that this doublet and triplet were related that the (two) protons giving the doublet and the (one) proton giving the triplet are coupled, and hence are attached to adjacent carbon atoms. 

Figure 13.14. Nmr spectrum of /i-propylbenzene. Moving downheld, we see the expected sequence of signals a, primary (3H) A, secondary (2H) c, benzylic (2H) and d, aromatic (5H). Signals a and c are each split into a triplet by the two secondary protons Hi,. The hve protons adjacent to the secondary protons—three on one side and two on the other—are, of course, not equivalent but the coupling constants, /ab and Jbo are nearly the same, and signal b appears as a sextet (5+1 peaks). The coupling constants are not exactly the same, however, as shown by the broadening of the six peaks.

Clearly the ammonia-formaldehyde reaction competes with the process but, using an excess of these reagents, the condensation can be made almost quantitative with respect to the tris(ethylene-diamine) complex. The specificity is decided by the chirality of the parent tris(ethylenediamine) complex since this decides the orientation of the gem-diamine and subsequent additions of the amino group to the adjacent imine. Unless the gem-diamine is oriented in the apical position, condensation to give the cap is prohibited. The A or A configuration of the ethylenediamine chelates then decides the orientation of the secondary proton if the amino methylene moiety is required to be apical A(S) or A(R). 

The first sum goes over all target elements i, while the index k in the second sum represents the reaction particle type (primary or secondary proton, secondary neutron). Na is Avogadro s number, Ai the mass number (in amu) of the target element i, q the... 

Figure 2. Comparison of measured (squares) and modelled (solid lines) Ne concentrations in the L/LL chondrite Knyahinya. The measured data are from Graf et al. (1990b), and the two model curves from Leya et al. (2000a) and Masarik et al. (2001). Both models assume a radius of Knyahinya of 45 cm and an exposure age of 39 Myr. Also shown are the individual contributions by primary protons and secondary protons and neutrons (Leya et al. 2000a). Note that even at the surface, most of the Ne is produced by secondary particles.

The next important postulate of Mitchell s theory concerns the consumers of the energy produced by primary pumps and presupposes the presence in the organella membranes of secondary proton pumps which use the transmembrane proton flow for ATP synthesis and a number of other processes. Essential to this theory is the... 

In MALDl (matrix-assisted laser desorption/ionization), the ionization process occurs in two steps an initial primary ionization followed by a secondary reaction [28]. During primary ionization, the ions are formed after the sample has absorbed the energy from the laser beam, and then, upon continuing laser beam irradiation, the analyte undergoes secondary neutralization reactions with free electrons until they become singly charged. Meanwhile, neutral analyte molecules evaporate and are charged by secondary protonation reaction. In this way, they can be detected. 

On the other hand, as might be anticipated, oxiranes (oxacyclopropanes, epoxides) react with mineral acids such as aqueous hydrochloride acid (HCl) under ionic conditions to produce the corresponding halohydrins. With oxiranes (oxacyclopropanes, epoxides) in which one of the carbon termini is primary and the other secondary, protonation is usually followed by an attack at the primary carbon, yielding a secondary alcohol (Equation 8.45). 

Returning to coupled protons, for Rapid and Slow, we have so far considered only the strongly coupled protons. In fact, structure (d) of Scheme 1, rather than structure (a), must represent these species. We have little information as to the nature of the proton-bearing atom, X. Indeed, it is possible that two or more atoms rather than a single atom intervene between the secondary proton and the molybdenum atom. Certainly the possiblity that X is nitrogen is not excluded, nor is its being oxygen or sulfur, but located in a different type of orbital from Y, so as to account for the weaker cou-... 

The mechanism of the chemiluminescent decomposition of secondary peroxy-esters shows similar features [7], in that the loss of the secondary proton allows electron transfer to the activator radical cation. Activators are fluorescent compounds of low ionisation potential. In the example shown below the activator is not consumed, and the products, acetophenone and acetic acid, are formed quantitatively. The unactivated decomposition is very closely related to peroxide decomposition generally, and it is not surprising to find that the quantum yield is very low. 

If electron transfer was occurring from the quinoxaline nucleus in the adduct, then a correlation between the electron withdrawing power of the groups X and the quantum yield should be observed. This was not the case. Although the light emission is absolutely dependent on having a secondary proton available, the details of the excitation step have still to be discovered. 

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