Bransted acid-base theory

From our previous treatment of the Arrhenius, Bransted and Lewis acid-base theories, the importance of the choice between the divergent solvent types clearly appeared if we now confine ourselves to solvents to which the proton theory in general is applicable, this leads to a classification of eight classes as already proposed by Bronsted35,36 (Table 4.3). 

In 1923, the same year that Bransted and Lowry came up with their idea of what acids and bases were, an American chemist named Gilbert Newton Lewis began to work on his own acid-base theory. Lewis defined acid as any substance that accepted an electron pair. A base, on the other hand, is any substance that donates an electron pair. 

The acids (proton donors) and bases (proton acceptors) are labeled below their formulas. Remember that a proton, in Bransted-Lowry acid-base theory, is H+. 

According to the Arrhenius theory, acids (HA) are substances that dissociate in water to produce H + (aq). Bases (MOH) are substances that dissociate to yield OH aq). The more general Bransted-Lowry theory defines an acid as a proton donor, a base as a proton acceptor, and an acid-base reaction as a proton-transfer reaction. Examples of Bronsted-Lowry acids are HC1, NH4+, and HSO4- examples of Bronsted-Lowry bases are OH-, F-, and NH3. 

In the Bransted-Lowry theory, every acid-base reaction creates its conjugate acid-base pair. In the above reaction HCl is an acid which, after giving up a proton, becomes a conjugate base, Cl . Similarly, water is a base which, after accepting a proton, becomes a conjugate acid, the hydronium ion. 

This reaction is essentially an acid-base process, which is most conveniently explained in terms of the Bransted-Lowry theory of acids and bases (see Section 1.23). 

Acidity and basicity are fundamental properties of organic compounds, and acid-base reactions are essential steps in many organic transformations. Although there are several definitions of acidity and basicity, the Bransted theory and the Lewis theory are used most often in organic chemistryIn Lewis theory, an acid is an electron pair acceptor and a base is an electron pair donor, as in the reaction of a trialkylamine as Lewis base with boron trifluoride as Lewis acid (equation 7.1). 

The Bransted-Lowry Theory of Acids and Bases COAL 2 Given the equation for a Br0nsted-Lowry acid-base reaction, explain how or why it can be so classified. 

Describe an acid-base reaction in the context of Bransted-Lowry theory, and identify conjugate acid-base pairs. 

B) From the foregoing, it is clear that the Arrhenius or solvents theory cannot work for aprotic solvents most adequate here is the Bransted-Lowry or proton theory, in which an acid is defined as a proton donor and a base as a proton acceptor, and under conditions such that the acid by donating its proton is converted into its conjugate base, and the base by accepting a proton is converted into its conjugate acid. This mutual relationship is illustrated by the following equilibrium reaction ... 

Acids are compounds that ionise to release hydrogen ions, or protons, to their surroundings. Bases are compounds that can accept hydrogen ions. This is called the Bransted-Lowry definition of acids and bases (named after yet another Scandinavian chemist, Johannes Nicolaus Bronsted, and Thomas Martin Lowry, who was British). There are other ways of explaining acidity and basicity, but the Bransted-Lowry theory works most of the time, and will be used throughout this book. 

Section 17.2 The Bransted-Lowry Theory of Acids and Bases... 

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