Bases as proton acceptors

Bronsted theory a theory of acids and bases that defines acids as proton donors and bases as proton acceptors. 

A base is a substance that can accept a proton. (Some chemists describe Bronsted-Lowry bases as proton-acceptors. )... 

Acids may be defined as proton donors and bases as proton acceptors. A proton donor and its corresponding proton acceptor make up a conjugate acid-base pair (Fig. 2-16). Acetic acid (CH3COOH), a proton donor, and the acetate anion (CII.COO ), the corre-... 

This reaction is a formal asymmetric aldol addition following a modified Evans protocol. The enolate 26 is formed at 0 °C in the presence of one equivalent of titanium tetrachloride as Lewis acid and two equivalents diisopropylethylamine (Hunig s base) as proton acceptor. Selectively the Z-enolate is formed. The carbon-carbon bond formation takes place under substrate control of the Tvan.v-auxiliary, whose benzyl group shields the, v/-face of the enolate. 

In Chapter 2, we will concentrate on two definitions of acids and bases the Brpnsted-Lowry definition, which describes acids as proton donors and bases as proton acceptors, and the Lewis definition, which describes acids as electron pair acceptors and bases as electron pair donors. 

However, soon after the work of Lavoisier, Scheele prepared an acid which did not contain the element oxygen, namely hydrochloric acid. After the discovery of hydrochloric acid the element essential for the property of acidity became hydrogen. At the beginning of twentieth century, Johannes Bronsted and Thomas M. Lowry defined acids as substances which are proton donors and bases as proton acceptors. 

The base, as proton acceptor, deprotonates alkyl halide causing the removal of a halide anion. The reaction proceeds via the transition state in which both C-H and C-Br bonds break simultaneously. Such reactions are called concerted. The reaction is bimolecular because its rate depends on the concentrations of two molecular species, alkyl-bromide and the ethoxy anion. This mechanism is called the E2 elimination mechanism. 

Earlier definitions of acids and bases as species producing respectively hydrogen ions and hydroxyl ions are only valid in aqueous solution. The concept of Br nsted and Lowry, while extending the classical definition, does not exclude the treatment of Arrhenius for aqueous media. The extended view regards acids as proton donors and bases as proton acceptors regardless of whether substances concerned are ionic or neutral. A terse summary of this definition may be given as follows... 

These subjects are familiar to students who have completed but a single course in chemistry. There is even a pleasant conformity of definitions despite a long evolutionary development ranging from the first association of the properties of sour taste with ability to dissolve metals to the present widely accepted views of Brjifnsted. These regard acids as proton (H+) donors and bases as proton acceptors. Acidity then becomes some measure of the ability of a medium to donate protons. 

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