Proton donors water

A term applied to a solvent that can act as a proton donor. Water and ethanol are both protogenic and proto-philic. See Protophilic Amphiprotic... 

As a strong polar proton donor, water is strongly absorbed in most ionic liquids. In the extreme case, it is fully miscible with ionic liquids, such as [BMIM]Bp4 and [BMIMJCFsCOj. Even the hydrophobic ionic liquids can pick up a low concentration of water, resulting in a reduced absorption affinity for some organic compounds (27). The presence of water may, therefore, influence the performance of an ionic liquid in catalytic applications. 

The parallel occurrence of the two reactions at a low concentration of the proton donors (water, alcohols, phenols, acids) can lead to a very complicated kinetics. Thus, in the investigations of the order of the reaction of PhGE with an aliphatic amine (butylamine)31) the reaction order with respect to the amine concentration is a fractional one and depends on the reaction temperature thus, at 12, 28, 42 and 58 °C the values of the order are 1.8, 1.6, 1.4 and 1.2, respectively. In the whole temperature range, the initial rate is well described by a superposition of two reactions, one of which is proportional to the first and the other to the second power of the amine concentration. The contribution of each reaction depends on temperature, for their activation energies are different Et =42kJ-mol 1 and E2 = 25 kJ mol"1, respectively. 

Reduction of propargylic bromides. The reagent reduces propargylic bromides to allenes as the major products in the presence of a proton donor (water). Addition of HMPT suppresses reduction to acetylenes.2 Use of a protonic chiral reagent results in optically active allcncs. Highest inductions have been observed with ( —)-menthol and (— )-bomeol (about 20% ee).J... 

Somewhat more complicated than the complexes discussed earlier is the combination of water with ammonia. The IR spectral characteristics of this complex were calculated using a variety of basis sets and the results are presented in Table 3.49. Also presented in this table are comparable data computed at a correlated (MP2) leveF, for purposes of comparison. The red shift of the proton donor water molecule v. band is 103 cm , quite a bit lower... 

Gtmnal alkylation af ketones. Coates and Sowerby have reported a new method for site-selective geminal alkylation of ketones which involves reduction of the n-butylthiomethylene derivative of the ketone by lithium-ammonia to give a methyl-substituted cnolatc anion which can be alkylated in situ. The ketone, for example cyclohexanone (I), is condensed with ethyl formate and then transformed into the n-butylthiomethylene derivative (2) by reaction with n-butyl mercaptan (2, 53-54). This is then reduced with excess lithium in liquid ammonia at -33° with 2 eq. of a proton donor (water is usually used to avoid ovcralkylation). The lithium cnolate is then... 

When two molecules interact, there is often a small amount of electron flow from one to the other. For example, in the equilibrium geometry of the linear water dimer HO— H... OH2, the water molecule that is the proton acceptor has transferred about 0.05e to the proton donor water (9,10). The attractive energy associated with this charge transfer is the charge transfer energy and can be thought of as a mixing of an ionic resonance structure... 

Logs are also used to calculate the pH of acids and bases. Acids love to donate a positive charge (a proton), and are called proton donors. Water, H20, accepts the charge and becomes HsO+. Can you find the formula that is used to calculate pH Do acids have high or low pH values ... 

From these results, it becomes obvious that only those substrates which can act as proton-donors (water, alcohols, hydroquinone, xylene) can be photo-oxidized by n-conductors, but that the basic aniline cannot. Chemisorbed negative oxygen unites with protons coming from the substrate, and the donor atom in the catalyst gets its electron back from the substrate anion. It is probable that mechanisms similar to that formulated above are involved in all these cases. 

When acetic acid reacts with water, water acts as a base, or a proton acceptor. But in the reaction with ammonia (see the preceding section), water acts as an acid, or a proton donor. Water can act as either an acid or a base, depending on what it s combined with. Substances that can act as either an acid or a... 

It can fairly be stated that water is the bane of the EPR experimentalist s existencel As a solvent, water increases molecular mobility and rates of reaction, redudng radical lifetimes. As a proton donor, water increases the rates of radical quendiing. These two effects seem obvious. Less intuitive, however, is the reduction ct EPR signal intensity by non-iesonant absorption of microwave enmgy tty water. 

On polarograms for diallylaminoethyl esters of acrylic and methacrylic acids in anhydrous dimethylformamide a one-electron reduction wave appears, which gradually increases to the two-electron level when proton donors (water, phenol, propargyl alcohol) are added to the solution [71]. The stronger the proton donors, the lower the concentrations at which the wave increases at the same time, the... 

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... 

Organohthium and organomagnesium compounds are stable species when prepared m suitable solvents such as diethyl ether They are strongly basic however and react instantly with proton donors even as weakly acidic as water and alcohols A proton is transferred from the hydroxyl group to the negatively polarized carbon of the organometallic compound to form a hydrocarbon... 

If the initiation reaction is much faster than the propagation reaction, then all chains start to grow at the same time. Because there is no inherent termination step, the statistical distribution of chain lengths is very narrow. The average molecular weight is calculated from the mole ratio of monomer-to-initiator sites. Chain termination is usually accompHshed by adding proton donors, eg, water or alcohols, or electrophiles such as carbon dioxide. 

Some materials such as water, alcohols, carboxylic acids and primary and secondary amines may be able to act simultaneously as proton donors and acceptors. Cellulose and poly(vinyl alcohol) are two polymers which also function in this way. 

Proton donor/acceptors (amphoteric solvents) water, alcohols. 

On the Brpnsted theory (p. 51), solutions with concentrations of H3O+ greater than that in pure water are acids (proton donors), and solutions rich in OH are bases (proton acceptors). The same classifications follow from the solvent-system theory of acids and bases... 

Acid-base reactions in anhydrous HF are well documented. Within the Brpnsted formalism, few if any acids would be expected to be sufficiently strong proton donors to be able to protonate the very strong proton-donor HF (p. 51), and this is borne out by observation. Conversely, HF can protonate many Brpnsted bases, notably water. 

Strong protonic acids can affect the polymerization of olefins (Chapter 3). Lewis acids, such as AICI3 or BF3, can also initiate polymerization. In this case, a trace amount of a proton donor (cocatalyst), such as water or methanol, is normally required. For example, water combined with BF3 forms a complex that provides the protons for the polymerization reaction. 

However, they can also be prepared by metal exchange from alkali-metal phthalocyanines. If proton donors like hydrochloric acid, water or methanol are added to the reaction mixture of a freshly prepared alkali-metal phthalocyanine, metal-free phthalocyanines (PcH2) are formed (see Section 2.1.4.1,). If, on the other hand, the appropriate metal salt is added to a solution of an alkali-metal phthalocyanine, the product is the metalated compound (PcM) (see Section 2.1.6.). 

Although water was used as a proton donor in this preparation, drying of the liquid ammonia and ether was carried out so that the lithium-ammonia solution would not be exposed to water during preparation and so that the amount of water added could be accurately controlled. 

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