Bronsted -Lowry base strengths

Backbone (protein), 1028 Backside displacement. reaction and.363-364 von Baeyer, Adolf, 113 Baeyer strain theory, 113-114 Bakelile, structure of, 1218 Banana, esters in, 808 Barton, Derek, H. R., 389 Basal metabolic rate, 1169 Basal metabolism. 1169-1170 Base, Bronsted-Lowry, 49 Lewis, 57, 59-60 organic, 56-57 strengths of, 50-52 Base pair (DNA), 1103-1105 electrostatic potential maps of. 

Bronsted-Lowry acid, 49 conjugate base of, 49 strengths of, 50-52 Bronsted-Lowry base, 49 conjugate acid of, 49 strengths of, 50-52 Brown, Herbert Charles. 223 Butacetin, structure of. 833 1,3-Butadiene, 1,2-addition reactions of, 487-489... 

On the above basis it is, in principle, unnecessary to treat the strength of bases separately from acids, since any protolytic reaction involving an acid must also involve its conjugate base. The basic properties of ammonia and various amines in water are readily understood on the Bronsted-Lowry concept. 

Base strength refers to the relative tendency to produce OH- ions in aqueous solution by (1) the dissociation of soluble metal hydroxides or (2) by ionization reactions with water using Arrhenius theory. A more general definition, applying Bronsted-Lowry theory, is that base strength is a measure of the relative tendency to accept a proton from any acid. 

There are several definitions of acids and bases. According to the Bronsted-Lowrv definition, an acid is a proton donor and a base is a proton acceptor. Any compound that has a hydrogen can potentially act as a Bronsted-Lowry acid (although the strength of the acid can vary enormously). Therefore, H—A is used as a general representation for an acid. To accept a proton, most bases... 

Before continuing on to the last definition of acids and bases, it will be helpful to consider the definitions for strong and weak acids within the context of the Bronsted-Lowry model of acids and bases. The definitions are really an extension of the Arrhenius ideas. In the Arrhenius definitions, strong acids and bases were those that ionize completely. Most Bronsted-Lowry acids and bases do not completely ionize in solution, so the strengths are determined based on the degree of ionization in solution. For example, acetic acid, found in vinegar, is a weak acid that is only about 1 percent ionized in solution. That means that when acetic acid, HC2H302, is placed in water, the reaction looks like ... 

In both the Arrhenius theory and the Bronsted-Lowry theory, acids and bases form ions in solution. Many characteristics of acid-base behaviour are linked to the number of ions that form from a particular acid or base. One of these characteristics is strength. 

It is difficult to quantify the"hardness"or"softness" of a Lewis acid or base. We cannot measure a pKa value, as is the case when assessing the strength of Bronsted-Lowry acids. 

Conversely, in Bronsted-Lowry terminology (Section 10-4), the order of increasing base strength of the anions of these acids is... 

The polar O-H bond of alcohols makes them weak acids. By the Bronsted-Lowry definition, acids are hydrogen ion donors and bases are hydrogen ion acceptors in chemical reactions. Strong acids are 100% ionized in water and weak acids are only partially ionized. Weak acids establish an equilibrium in water between their ionized and unionized forms. This equilibrium and the strength of an acid is described by the acidity constant, Ka. Ka is defined as the concentrations of the ionized forms of the acids (H30+ and A-) divided by the un-ionized form... 

The strength of a Bronsted-Lowry acid is quantified in terms of the magnitude of the equilibrium constant for the ionization reaction in which the solvent acts as the base, e.g. for the aqueous system, the general reaction is ... 

The relative strengths of Bronsted-Lowry bases can be measured based on their K, base dissociation constants. A strong base, such as NaOH or Mg(OH)2, has a Kb > I and will dissociate 100% in aqueous solution. The definition of K for the generic weak base A is given by Equation (14.9) ... 

The strength of Lewis acid-base interactions cannot be expressed in terms similar to the acidity and basicity constants. K. and of the Bronsted-Lowry theory. Consequently an equilibrium constant resembling the protolytic constant of Bronsted acid-base couples, Eq. (1), cannot be specified. Because of the broad variety of Lewis acid-base interactions there would be as many acid strength scales as there are interacting bases. 

Many organic reactions involve the transfer of a proton by an acid-base reaction. An important consideration, therefore, is the relative strengths of compounds that could potentially act as Bronsted-Lowry acids or bases in a reaction. 

The strength of a Bronsted—Lowry acid depends on the extent to which a proton can be separated from it and transferred to a base. Removing the proton involves breaking a bond to the proton, and it involves making the conjugate base more electrically negative. 

The Bronsted-Lowry Theory 10-5 The Autoionization of Water 10-6 Amphoterism 10-7 Strengths of Acids 10-8 Acid-Base Reactions in Aqueous Solutions... 

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