Lowry-Bronsted Acid-Base Reactions

It follows from this equation that the products of a Bronsted-Lowry acid-base reaction, BH+ and A-, are themselves acids and bases. The species BH+ produced when the base B accepts a proton from HA can itself donate a proton back to A-, meaning that it is a Bronsted-Lowry acid. Similarly, the species A- produced when HA loses a proton can itself accept a proton back from BH+, meaning that it is a Bronsted-Lowry base. Chemical species whose formulas differ only by one... 

Related ammonium salts derived from amines, such as [CH3NH3]C1, [(CH3)2NH2]C1, and [(CH3)3NH]C1, also give acidic solutions because they too have cations with at least one dissociable proton. The pH of a solution that contains an acidic cation can be calculated by the standard procedure outlined in Figure 15.7. For a 0.10 M NH4C1 solution, the pH is 5.12. Although the reaction of a cation or anion of a salt with water to produce H30+ or OH - ions is sometimes called a salt hydrolysis reaction, there is no fundamental difference between a salt hydrolysis reaction and any other Bronsted-Lowry acid-base reaction. 

Bronsted-Lowry acid-base reactions always result in the transfer of a proton from an acid to a base. 

Problem 6.15 Draw an energy diagram for the Bronsted-Lowry acid-base reaction of CH3CO2H with "OCICHglg to form CH3CO2" and (CHglgCOH. Label the axes, starting materials, products, AH°, and Eg. Draw the structure of the transition state. 

Preparation of alkoxides—A Bronsted-Lowry acid-base reaction... 

Treatment of indene with NaNH2 forms its conjugate base in a Bronsted-Lowry acid-base reaction. Draw aii reasonable resonance structures for indene s conjugate base, and explain why the pKa of indene is lower than the pK of most hydrocarbons. 

A broader definition of acids and bases, which will be useful in quantitative calculations in this chapter, was proposed independently by Johannes Bronsted and Thomas Lowry in 1923. A Brensted-Lowry acid is defined as a substance that can donate a hydrogen ion, and a Bronsted-Lowry base is a substance that can accept a hydrogen ion. In a Bronsted-Lowry acid-base reaction, hydrogen ions are transferred from the acid to the base. When acetic acid is dissolved in water,... 

Most of the acids considered up to now have been uncharged species with the general formula HA. In the Bronsted-Lowry picture there is no reason why the acid should be an electrically neutral molecule. When NH4CI, a salt, dissolves in water, NH4 ions are present. These ionize partially by transferring hydrogen ions to water, a straightforward Bronsted-Lowry acid-base reaction ... 

The alkylammonium cation is called the conjugate acid of the amine. Write down the general equation for a Bronsted-Lowry acid/base reaction, labelling the acid and the base, and the related conjugate base and acid. 

The nucleophile, the ammonia molecule, is also acting as a base, while the electrophile, the proton, is also acting as an acid. So a base may also be thought of as a nucleophile, because both are electron rich species and seek positive centres. The above reaction between the ammonia and the proton may be classified as a Bronsted-Lowry acid/base reaction. It may also be classed as a Lewis acid/base reaction, depending on whether one views the ammonia as a proton acceptor or as a donor of a lone pair of electrons. 

Nucleophiles with a high charge density, such as hydroxide ions, tend to react more readily with electrophiles with a high charge density, such as protons. Thus, hard nucleophiles tend to react with hard electrophiles. The reaction of a hydroxide ion with a proton is also typical of a Bronsted-Lowry acid/base reaction. 

In this case, the hard hydroxide anion has removed the hard proton on the hydroxyl group to form an alkoxide ion in a simple Bronsted-Lowry acid/base reaction. Suggest what is the next step in this reaction, remembering that overall there is retention of the stereochemistry at the carbon bonded to the chlorine atom. 

We can describe Bronsted-Lowry acid-base reactions in terms of conjugate acid-base pairs. These are two species that differ by a proton. In the preceding equation, HF (acid2) and (basc2) are one conjugate acid-base pair, and H2O (bascj) and H30 (acidj) are the other pair. The members of each conjugate pair are designated by the same numerical subscript. In the forward reaction, HF and H2O act as acid and base, respectively. In the reverse reaction, H30 acts as the acid, or proton donor, and F acts as the base, or proton acceptor. 

Although the Arrhenius definitions of acid, base, and acid-base reaction are very useful, an alternate set of definitions is also commonly employed. In this system, a Bronsted-Lowry acid is a proton (H+) donor, a Bronsted-Lowry base is a proton acceptor, and a Bronsted-Lowry acid-base reaction is a proton transfer. Table 5.7 summarizes the definitions of acid and base in the Arrhenius and Bronsted-Lowry systems. 

Bronsted-Lowry acid-base reaction A chemical reaction in which a proton, H" ", is transferred. 

Bronsted-Lowry Acid A substance that donates protons, H, in a Bronsted-Lowry acid-base reaction. 

Note that Bronsted-Lowry acid-base reactions (proton donor-proton acceptor reactions) are encompassed by the Lewis model. For example, the reaction between a proton and an ammonia molecule, that is. 

Hydrogen ion transfer reactions. In these reactions, also known as Bronsted-Lowry acid-base reactions, a hydrogen ion is transferred from one species to another. Fluorite (Cap2) is etched by acids because a hydrogen ion is transferred from the acid to the fluoride ion and forms the molecule HF. 

The acid-base chemistry of amino acids is more complicated than shown in Equations 16.48 and 16.49, however. Because the COOH group can act as an acid and the NH2 group can act as a base, amino acids undergo a self-contained Bronsted-Lowry acid-base reaction in which the proton of the carboxyl group is transferred to the basic nitrogen atom ... 

Two classes of acid-base reactions are fundamental in organic chemistry Bronsted—Lowry and Lewis acid-base reactions. We start our discussion with Bronsted—Lowry acid—base reactions. 

Bronsted-Lowry acid-base reactions involve the transfer of protons. 

X-ray crystallographic data), a bicarbonate ion at the active site is shown in red, the zinc cation at the active site is green, a water molecule is shown in blue, and the basic sites that coordinate with the zinc cation (as Lewis bases) or remove the proton from water to form hydroxide (as Bronsted-Lowry bases) are magenta (these bases are nitrogen atoms from histidine imidazole rings). No hydrogen atoms are shown in any of these species. As you can see, a remarkable orchestration of Lewis and Bronsted-Lowry acid-base reactions is involved in catalysis by carbonic anhydrase. 

The Lewis definition of acids and bases is broader than the Bronsted-Lowry definition. According to the Lewis definition, acidity and basicity are described in terms of electrons, rather than protons. A Lewis acid is defined as an electron acceptor, while a Lewis base is defined as an electron donor. As an illustration, consider the following Bronsted-Lowry acid-base reaction ... 

Figure 18.7 Dissolving of an acid or base in water as a Bronsted-Lowry acid-base reaction. A,The acid HCI dissolving in the base water. B,The base NH3 dissolving in the acid water.

A Bronsted-Lowry acid-base reaction involves the transfer of a proton from the acid to the base. An ammonia molecule, with an unshared electron pair on the nitrogen, is the proton receiver-the base-in this reaction. See Section 17.2. 

Bronsted-Lowry acids and bases donate or accept protons. A Lewis acid or base accepts or donates a pair of electrons. Key Terms Bronsted-Lowry acid Bronsted-Lowry base Bronsted-Lowry acid-base reaction 1 lie polyprotic acid diprotic acid triprotic acid Ul IvO Lewis base Lewis acid-base reaction... 

Bronsted-Lowry Acid-Base Reactions Hydrogen chloride gas escapes from a hydrochloric acid solution and combines with ammonia gas that has escaped from an aqueous ammonia solution. The resulting cloud is solid ammonium chloride that is dispersed in air. 

In a Bronsted-Lowry acid-base reaction, protons are transferred from one reactant (the acid) to another (the base). Figure 2.1 shows the reaction between the Bronsted-Lowry acid HCl and the Bronsted-Lowry base NH3. 

In general, Bronsted-Lowry acid-base reactions are equilibrium systems meaning that both the forward and reverse reactions occur. They involve two acid-base pairs, known as conjugate acid-base pairs. 

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