Bases, ionization

Acids differ m the degree to which they ionize Those that ionize completely are called strong acids, those that do not are weak acids Likewise strong bases ionize completely weak bases do not... 

It is believed that a reactive ground-state species, the zwitterion A, is an intermediate and that it rearranges to the observed product. To test this mechanism, generation of species A by nonphotochemical means was undertaken. a-Haloketones, when treated with strong base, ionize to such dipolar intermediates. Thus, the bromoketone 6 is a potential precursor of intermediate A ... 

Kb is also widely called the base ionization constant. 

In the presence of a base B, water acts as an acid by donating a proton, and the equiiibrium constant for the transfer of a proton from water to a base is caiied the base ionization constant (Zjj) ... 

In the above example, the anion (A) functions as a base when it combines with a hydrogen ion. (By definition, any substance that combines with hydrogen ions is a base. Like strong acids, strong bases ionize completely in a dilute aqueous solution.) Thus NaOH dissolves in water to form hydroxide ions, which in turn function as a base when they combine with hydrogen ions to form water, as shown by the general equations... 

KEY TERMS acid-base indicator conjugate base ionization... 

Soreq [41] has developed a nitrogen-rich (31% by weight) N-based ionization detector liquid scintillator based on di-methyl-tetrazole that is resonance sensitive (24% efficient for resonant photons) and is well suited for the explosive detection application. 

Kjj is the base dissociation constant, or base ionization constant, that measures a base s strength. Some values are given for bases in Table 3. 

ADMET Predictor Constitutional, functional group counts, topological, E-state, Moriguchi descriptors, Meylan flags, molecular patterns, electronic properties, 3D descriptors, hydrogen bonding, acid-base ionization, empirical estimates of quantum descriptors 297... 

The activities of many enzymes vary with pH in the same way that simple acids and bases ionize. This is not surprising, since, as we saw in Chapter 1, the active sites generally contain important acidic or basic groups (Table 5.1). It is to be expected that if only one protonic form of the acid or base is catalyti-cally active, the catalysis will somehow depend on the concentration of the active form. In this chapter we shall see that kcM, KM, and kcJKM are affected in different ways by the ionizations of the enzyme and enzyme-substrate complex. 

The charge properties of amino acids are very important in determining the reactivity of certain amino acid side chains and in the properties they confer on proteins. The charge properties of amino acids in aqueous solution may best be considered under the general treatment of acid-base ionization theory. We find this treatment useful at other points in the text as well. 

All spectroscopic lines have a natural line width, and this can be of great use to the kineticist. This natural line width is determined by the lifetime of the excited state of the molecule. If this is short the line width is broad, while longer lifetimes give more sharply defined lines. If reaction occurs, this can alter the lifetime of the excited state and so change the natural line width of the transition. A detailed spectroscopic analysis gives relations between the width of the line, the lifetime of the reacting species and the rate constant for the reaction. This has proved a very important tool, especially for reactions in solution such as proton transfers and acid/base ionization processes. 

In performing a calculation based on an acid or base ionization constant expression such as Eqs. (13-7) or (13-8), there are often many unknowns. Remember that in an algebraic problem involving multiple unknowns, one needs as many equations as there are unknowns. The equilibrium constant expression itself is one equation, and the Kw expression is always available. Two other types of equation are often useful equations expressing... 

Bases are those substances that ionize in water to release OH- ions. NaOH is a strong base, ionizing completely in water to yield Na+ and OH- ions. However, even those hydroxide bases that do not dissolve... 

Bases accept (or take) hydrogen ions. In water, the strongest possible base is the hydroxide ion, OH-. A strong base ionizes essentially 100% to produce the OH- ion, so a strong base is a soluble ionic hydroxide. Like all soluble ionic compounds, ionic hydroxides are strong electrolytes and dissociate completely... 

This same process can be seen in bases. Consider the equilibrium of a weak base ionization, as shown below ... 

At this point, the calculation becomes a little different. Because the benzoate ion is a base, the equilibrium constant expression must be the base ionization constant, Kb. You haven t been given the value of Kb, however, so you will have to generate it using Equation 13.8 ... 

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