Proton-donor theory

Ugolini, F. C. (1987). The proton donor theory Part I and II. Soil Sci. Amer. Ann. Meet., Agronomy, November 28-December4, abstract, p. 233, Atlanta, Georgia,... 

When Berzelius theory of valence was discarded, primarily as the result of Faraday s discovery of the laws of electrolysis, the theory of acids and bases founded upon it also had to be abandoned. Doubt had already been cast on it by Davy s demonstration that hydrochloric acid did not contain oxygen. There was no doubt of the acidity of hydrochloric acid so, still thinking in terms of an elementary acidifying principle, many chemists came to regard hydrogen as the one element necessary for acid properties. Ideas regarding bases did not become so definite until the advent of the proton-donor theory. 

Thus the electronic theory pictures the reaction in exactly the same manner as the proton-donor theory. 

A more general theory of acids and bases was devised independently by Johannes Br0n sted (Denmark) and Thomas M Lowry (England) m 1923 In the Brpnsted-Lowry approach an acid is a proton donor, and a base is a proton acceptor The reaction that occurs between an acid and a base is proton transfer... 

Hydrogen was recognized as the essential element in acids by H. Davy after his work on the hydrohalic acids, and theories of acids and bases have played an important role ever since. The electrolytic dissociation theory of S. A. Arrhenius and W. Ostwald in the 1880s, the introduction of the pH scale for hydrogen-ion concentrations by S. P. L. Sprensen in 1909, the theory of acid-base titrations and indicators, and J. N. Brdnsted s fruitful concept of acids and conjugate bases as proton donors and acceptors (1923) are other land marks (see p. 48). The di.scovery of ortho- and para-hydrogen in 1924, closely followed by the discovery of heavy hydrogen (deuterium) and... 

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... 

According to this theory, an acid is defined as a proton donor and a base as a proton acceptor (a base must have a pair of electrons available to share with the proton this is usually present as an unshared pair, but sometimes is in a 7t orbital). An acid-base reaction is simply the transfer of a proton from an acid to a base. (Protons do not exist free in solution but must be attached to an electron pair). When the acid gives up a proton, the species remaining still retains the electron pair to which the proton was formerly attached. Thus the new species, in theory at least, can reacquire a proton and is therefore a base. It is referred to as the conjugate base of the acid. All acids have a conjugate base, and all bases have a conjugate acid. All acid-base reactions fit the equation... 

In the Brpnsted picture, the acid is a proton donor, but in the Lewis picture the proton itself is the acid since it has a vacant orbital. A Brpnsted acid becomes, in the Lewis picture, the compound that gives up the actual acid. The advantage of Lewis theory is that it correlates the behavior of many more processes. For example, AICI3 and BF3 are Lewis acids because they have only 6 electrons in the outer shell and have room for 8. Both SnCU and SO3 have eight, but their central elements, not being in the first row of the periodic table, have room for 10 or 12. Other Lewis acids are simple cations, like Ag. The simple reaction A + B- A—B is not very common in organic chemistry, but the scope of the Lewis picture is much larger because reactions of the types... 

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 ... 

C) The Bronsted-Lowry or proton theory interprets the acid-base reaction as a mere proton exchange between the acid (proton donor) and the base (proton acceptor) however, the Lewis theory or electron theory interprets the reaction as a donation and acceptance of a lone pair of electrons, where the... 

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

In this reaction, the acetate ion is functioning as a base. On the other hand, Cl- has very littie tendency to function as a base because it comes from FI Cl, which is a very strong proton donor. According to the Bronsted-Lowry theory, the species remaining after a proton is donated is called the conjugate base of that proton donor. 

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+. 

An acid is defined as a proton donor within the Lowry-Brpnsted theory (see Chapter 6). Molecules of acid ionize in aqueous solution to form an anion and a proton, both of which are solvated. An acid such as ethanoic acid (VI) is said to be weak if the extent to which it dissociates is incomplete we call it strong if ionization is complete (see Section 6.2). 

Equilibria involving acids and bases are discussed from within the Lowry-Br0nsted theory, which defines an acid as a proton donor and a base as a proton acceptor (or abstracter ). The additional concept of pH is then introduced. Strong and weak acids are discussed in terms of the acidity constant Ka, and then conjugate acids and bases are identified. 

The Lowry-Bronsted theory says an acid is a proton donor. 

Lowry is best known to chemistry students through the tradition of eponymony, since the proton theory of acidity is known as the "Bronsted/Lowry theory" of proton donors. His most important experimental investigation likely was a long series of studies on optical rotatory dispersion.49 For our purposes, there is special interest in his discovery of mutarotation in camphor derivatives and his theory of dynamic tautomerism, which led him to an ionic theory of organic reaction mechanisms. 

The concepts of the Lowry-Bronsted theory may explain the various reactions that take place during many non-aqueous titrations. Thus, an acid is a proton donor and a base is a proton acceptor. Therefore, when an acid HA undergoes dissociation it gives rise to a proton and the conjugate base A of the acid ... 

Similarly, dihydrogen-bonded complexes of LiH with a variety of proton donors (e.g., HF, HCl, H2O, H2S, and NH3) have been studied by Kulkami [3] and Kulkami and Srivastava [4]. Some details of these studies are very interesting and show a dramatic dependence of dihydrogen bonding on the natme of proton donors and the level of theory. All the possible structures for these systems have been optimized at the HF/6-31++G(d,p) and MP2/6-31-H-G(d,p) levels, and the nature of stationary points has been examined by calculating their vibrational frequencies at the MP2/6-31++G(d,p) level. 

NH4-CH4]+ complex in the gas phase [36]. Topological analysis of the electron density performed in the framework of AIM theory shows the bond critical points on the H- H directions with pc values of 0.013 an. It is interesting that the electron density in this complex is larger than that obtained for the BH4 - CH4 dihydrogen-bonded system (pc = 0.007 an), the CH4 molecule of which acts as a proton donor. In accordance with the electronic density, the H- H distances in the BH4 - H4C complex were remarkably longer than 2.4 A (2.797, 2.929,... 

In 1923, Johannes Br nsted and his English counterpart Thomas Lowry independently developed a more general acid-base theory. According to the Br nsted-Lowry model, an acid is a proton (H+) donor and a base is a proton acceptor. Each proton donor (acid) has its pair (conjugate) proton acceptor (base). In an acid-base reaction, H (proton) is transferred from an acid to a base. For example ... 

ACIDS AND BASES. The conventional definition of an acid is that it is an electrolyte that furnishes protons, i.e.. hydrogen ions. H+. An acid is sour to the taste and usually quite corrosive. A base is an electrolyte that furnishes hydroxyl ions, OH . A base is bitter to die taste and also usually quite corrosive. These definitions were formulated in terms of water solutions and. consequently, do not embrace situations where some ionizing medium other than water may be involved. In the definition of Lowry and Brnsted, an acid is a proton donor and a base is a proton acceptor. Acid-base theory is described later. 

In 1923, the Danish chemist Johannes Bronsted proposed that an acid is a proton donor and a base is a proton acceptor. The same definitions were proposed independently by the English chemist Thomas Lowry, and the theory based on them is widely called the Bronsted-Lowry theory of acids and bases (Fig. 10.1). 

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