Protonated organic compounds

Organozinc addition reactions to unsaturated systems lead to an intermediate zinc compound which is in most cases further hydrolyzed to give the corresponding protonated organic compound. This intermediate can also be trapped by reaction with electrophiles (see Electrophile) (E+) such as aldehydes, acyl chlorides, organic halides, silyl halides, and so on. Depending on the nature of the electrophile (see... 

The electrochemistry of a protonated organic compound differs in many cases from that of the neutral molecule, and the strength of the acid necessary for protonation of the substrate must be considered. Sulfuric acid and acetic acid, often containing some water, have generally been used. When high acidities are desired, fluorosulfonic acid may be used. 

In many acids the acidic proton is bonded to oxygen Such compounds can be con sidered as derivatives of water Among organic compounds the ones most closely related to water are alcohols Most alcohols are somewhat weaker acids than water methanol IS slightly stronger... 

Instead of measuring chemical shifts m absolute terms we measure them with respect to a standard—tetramethylsilane ( 113)481 abbreviated TMS The protons of TMS are more shielded than those of most organic compounds so all of the signals m... 

The measurements of concentration gradients at surfaces or in multilayer specimens by neutron reflectivity requires contrast in the reflectivity fiDr the neutrons. Under most circumstances this means that one of the components must be labeled. Normally this is done is by isotopic substitution of protons with deuterons. This means that reflectivity studies are usually performed on model systems that are designed to behave identically to systems of more practical interest. In a few cases, however (for organic compounds containing fluorine, for example) sufficient contrast is present without labeling. 

Most organic compounds are bases, that is, they are capable of accepting a proton. The best-studied organic bases are the moderately strong ones, which will receive a proton in dilute aqueous solutions amines are the most important examples. The pKa value of the protonated base, referred to the infinitely dilute aqueous solution, is the usual measure of base strength, and the pH of the solution is a quantitative measure of solvent acidity, or ability to transfer a proton. 

Several types of proton transfer reactions can be studied conveniently by a neutral product analysis. Until now, the most extensive investigations have been concerned with (1) proton transfer from H3+ and CH5 + to various hydrocarbon molecules, and (2) the transfer of a proton from carbonium ions to larger olefins or other organic compounds. 

Aerobic respiration. Many organisms carry out aerobic respiration in which enzymes remove electrons from organic compounds and pass them through a chain of carriers including flavoproteins and cytochromes located in intracellular membranes (Fig. 3-4) until finally they are used to reduce oxygen to produce water. ATP is produced by an enzyme called ATPase, that is located in the cell membrane, and the process is driven by a proton gradient across the membrane. 

There remains one topic to be discussed in our survey of chemical bonding in organic compounds. For most compounds, all the molecules have the same structure, whether or not this structure can be satisfactorily represented by a Lewis formula. But for many other compounds there is a mixture of two or more structurally distinct compounds that are in rapid equilibrium. When this phenomenon, called tauto-merism, exists, there is a rapid shift back and forth among the molecules. In most cases, it is a proton that shifts from one atom of a molecule to another. 

Numerous colorless organic compounds with extended jt-electron systems can be converted to colored cations or anions with polymethyne chromophore by protonation or deprotonation. The intense coloration of the corresponding salts is usually attributable to the fact that the lone pairs of electrons of the heteroatoms participate in the mesomerism of the conjugated n-electron systems [4]. 

Besides water, the most common weak base is ammonia, NH3, whose proton transfer equilibrium with water appears in Section 16-. Many other weak bases are derivatives of ammonia called amines, hi these organic compounds, one, two, or three of the N—H bonds in ammonia have been replaced with N—C bonds. The nitrogen atom in an amine, like its counterpart in ammonia, has a lone pair of electrons that can form a bond to a proton. Water does not protonate an amine to an appreciable extent, so all amines are weak bases. Table 17-4 lists several examples of bases derived from ammonia. 

When the Au(I) complex [Au(CGF5)(tht)j reacts with lithium l-methylimidazol-2-yls the organic compound is protonated or alkylated and the carbene complexes are obtained [67] (see Figure 3.3). 

Electron impact ionisation (El) stands for extensive fragmentation, but also produces molecular ions. The other ionisation methods shown in Table 6.10 mainly generate quasi-molecular ions for various compound classes. Protonation of organic compounds is one of the most fundamental processes of Cl, FAB and ESI mass spectrometry. Apart from electrospray (ESI), which... 

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