Br0nsted acid-base theory

Two acid-base theories are used in organic chemistry today the Br0nsted theory and the Lewis theory. These theories are quite compatible and are used for different purposes. ... 

An acid in the Br0nsted-Lowery theory is an H+ donor and a base is an H+ acceptor. In the Brpnsted-Lowery acid-base theory, there is a competition for an H+. Consider the acid-base reaction between acetic acid, a weak acid, and ammonia, a weak base ... 

At about the same time that Br0nsted proposed his acid-base theory, Lewis put forth a broader theory. A base in the Lewis theory is the same as in the Br0nsted one, namely, a compound with an available pair of electrons, either unshared or in a 71 orbital. A Lewis acid, however, is any species with a vacant orbital. In a Lewis acid-base reaction the unshared pair of the base forms a covalent bond with the vacant orbital of the acid, as represented by the general equation... 

The purpose of this chapter is to give an introduction to the subject of nucleophilicity. The chapters of the present volume are collected into five groups (1) Marcus theory, methyl transfers, and gas-phase reactions (2) Br0nsted equation, hard-scft acid-base theory, and factors determining nucleophilicity (3) linear free-energy relationships for solvent nucleophilicity (4) complex nucleophilic reactions and (5) enhancement of nucleophilicity. The present chapter is divided in the same way, giving an introduction to each of the five topics followed by a description of key points in each chapter as they relate to current studies of nucleophilicity and the other chapters of the book. 

The complete book is based on the acid-base theory of Br0nsted (Brbnsted) and Lowry, according to whom acids are proton donators and bases are proton acceptors. AU other acid-base theories are not discussed here, and we refer to the respective literature [9, 17]. 

Following is another example of adding a proton. Here, the proton is added across the pi bond of the C — C double bond. The compounds below are labeled as proton donor and proton acceptor, terms used to describe Br0nsted acids and bases. They can also be labeled according to Lewis acid-base theory as electrophile and nucleophile. ... 

In 1923, Johannes Br0nsted in Denmark and Thomas Lowry in England proposed an acid-base theory that took into account this behavior of hydrogen ions. They defined an acid as any hydrogen-containing snbstance that donates a proton (hydrogen ion) to another substance and a base as any substance that accepts a proton. 

Br0nsted-Lowry acid-base theory, proton-transfer reaction, proton source, proton remover, amphoteric... 

Johannes Nicolaus Brdnsted (1879-1947). Danish chemist. In addition to his theory of acids and bases, Br0nsted worked on thermodynamics and the separation of mercury into its isotopes. In some books. Brpnsted acids and bases are called Bronsted-Lowry acids and bases. Thomas Martin Lowry (1874—1936). English chemist. Brpnsted and Lowry developed essentially the same acid-base theory independently in 1923. 

The Arrhenius concept was of basic importance because it permitted quantitative treatment of a number of acid-base processes in aqueous solutions, i.e. the behaviour of acids, bases, their salts and mixtures of these substances in aqueous solutions. Nonetheless, when more experimental material was collected, particularly on reaction rates of acid-base catalysed processes, an increasing number of facts was found that was not clearly interpretable on the basis of the Arrhenius theory (e.g. in anhydrous acetone NH3 reacts with acids in the absence of OH- and without the formation of water). It gradually became clear that a more general theory was needed. Such a theory was developed in 1923 by J. N. Br0nsted and, independently, by T. M. Lowry. 

The limitations of the Arrhenius theory of acids and bases are overcome by a more general theory, called the Bronsted-Lowry theory. This theory was proposed independently, in 1923, by Johannes Br0nsted, a Danish chemist, and Thomas Lowry, an English chemist. It recognizes an acid-base reaction as a chemical equilibrium, having both a forward reaction and a reverse reaction that involve the transfer of a proton. The Bronsted-Lowry theory defines acids and bases as follows ... 

DEGREE OF DISSOCIATION HENDERSON-HASSELBALCH EQUATION ACID-BASE EQUILIBRIUM CONSTANTS BR0NSTED THEORY LEWIS ACID ACIDITY FUNCTION LEVELING EFFECT ACIDITY FUNCTION ACID-LABILE SULFIDES ACID PHOSPHATASE ACONITASE... 

The Br0nsted-Lowery theory (usually called the Br0nsted theory), advanced by these workers in 1923, is more comprehensive than the Arrhenius theory. According to this theory, an acid-base reaction is characterized as a reaction in which a proton is transferred from one species (the acid, the proton donor) to another (the base, the proton acceptor). There can be no acid without a base neither exists in isolation because the proton must be transferred to some other species. According to this theory, HC1 is an acid because when it is placed in water, it acts as a proton donor,... 

INTERPRETATION OF OTHER ACID-BASE REACTIONS WITH THE BR0NSTED-LOWRY THEORY As already outlined, the great advantage of the Brensted-Lowry theory lies in the fact that any type of acid-base reaction can be interpreted with the simple reaction scheme... 

In his oxonium theory of acids and bases (91), Werner anticipated by 16 years the now generally accepted views of Br0nsted (7, 8) and Lowry (40j 41) y which accords that acids are proton donors and bases are proton acceptors. Yet, despite the fact that Werner was the first to emphasize the critical role of the solvent in acid-base phenomena, his contributions to this field are almost universally ignored. 

In contrast to the Br0nsted-Lowry theory, which emphasizes the proton as the principal species in acid-ba.se reactions, the definition proposed by Lux and extended by Floods describes acid-base behavior in terms of the oxide ion. This acid-base concept was advanced to treat nonprotonic systems which were not amenable to the Br0nsted-Lowry definition. For example, in high-temperature inorganic melts, reactions such as the following take place ... 

Br0nsted Equation, Hard-Soft Acid-Base (HSAB) Theory, and Factors Determining Nucleophilicity... 

The theory of solvent systems is suitable for ionizable solvents, but it is not ap-phcable to acid-base reactions in nonionizable solvents such as benzene or diox-ane. In 1923, Br0nsted and Lowry separately described what is now known as the Br0nsted-Lowrv theory. This theory states that an acid is any substance that can donate.a proton, and a base is any substance that can accept a proton. Thus, we can write a half-reaction ... 

A meticulous experimenter, Thomas Lowry is best known for his conceptualization of acid-base chemistry. Studies of nitrogenous compounds led Lowry to question fundamental aspects of the role of hydrogen during acid-base reactions. Three months before Br0nsted published his theory, Lowry released his own similar thoughts on proton acceptors and donors In print. 

The Br0nsted-Lowry theory conjugate acid-base pairs... 

An even more general theory of acids and bases was given by the American chemist G. N. Lewis in 1923. In this theory, an acid is an electron acceptor and a base is an electron donor. This is a more general theory than the Br0nsted-Lowry theory, because it allows the acid-base classification to be applied to reactions in which neither H (aq) nor OH (aq) play a role, or even to reactions in which there is no solvent. For example, the following are acid-base reactions in the Lewis theory... 

In Chapter 5 we saw that, in terms of the Br0nsted-Lowry theory, acid-base reactions involve proton transfer. Another large and important group of chemical reactions, particularly in aqueous solutions, involves electron transfer these are referred to as oxidation-reduction (or redox) reactions. Redox reactions are involved (1) in photosynthesis, which releases oxygen into the Earth s atmosphere (2) in the combustion of fuels, which is responsible for rising concentrations of atmospheric carbon dioxide (3) in the formation of acid precipitation and (4) in many chemical reactions in Earth sediments. 

The Arrhenius concept was the first successful theory of acids and bases. Then in 1923, Br0nsted and Lowry characterized acid-base reactions as proton-transfer reactions. According to the Br0nsted—Lowry concept, an acid is a proton donor and a base is a proton acceptor. The Lewis concept is even more general than the Br0nsted-Lowry concept. A Lewis acid is an electron-pair acceptor and a Lewis base is an electron-pair donor. Reactions of acidic and basic oxides and the formation of complex ions, as well as proton-transfer reactions, can be described in terms of the Lewis concept. 

However, the Lewis theory is more general than the Br0nsted-Lowry theory some reactions are classified as acid-base reactions under the Lewis definitions that are not regarded as acid-base reactions under the Br0nsted-Lowry theory. Therefore the terms Lewis acid and Lewis base are often reserved for species which are Lewis acids and bases, but which are not Br0nsted-Lowry acids and bases. 

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