Chemistry conjugate acid-base pairs

Conjugate add-base pairs Recall from Chapter 3 that the definition of adds and bases most useful to analytical chemistry is that of Bronsted, in which a conjugate acid-base pair is related by the reaction... 

The Br0nsted-Lowry definitions of acids and bases are widely used in organic chemistry. As noted in the preceding equation, the conjugate acid of a substance is formed when it accepts a proton from a suitable donor. Conversely, the proton donor is converted to its conjugate base. A conjugate acid-base pair always differ by a single proton. 

Solutions that contain a weak conjugate acid—base pair, such as those discussed in Section 17.1, resist drastic changes in pH when small amounts of strong acid or strong base are added to them. These solutions are called buffered solutions (or merely buffers). Human blood, for example, is a complex buffered solution that maintains the blood pH at about 7.4 (see the Chemistry and Life box on page 713). Much of the chemical behavior of seawater is determined by its pH, buffered at about 8.1 to 8.3 near the surface (see Chemistry and Life box on page 728). Buffered solutions find many important applications in the laboratory and in medicine ( FIGURE 17.1). 

New Core Chemistry Skills are added Identifying Conjugate Acid-Base Pairs (10.1), Using Le Chatelier s Principle (10.3), Calculating [H30 ] and [OH ] in Solutions (10.4), Writing Equations for Reactions of Acids and Bases (10.6), and Calculating Molarity or Volume of an Acid or Base in a Titration (10.6). 

The exact verbal definition of qualitative concepts is more often the province of philosophy than of physical science. However, the various definitions suggested for acids and bases have been closely linked with the development of physical chemistry and have often served to stimulate experimental work and to further our understanding of chemical processes, and we shall therefore devote some time to this subject. The definitions used in the remainder of this book will be those proposed by Bronsted in 1923, namely, An acid is a species having a tendency to lose a proton, and a base is a species having a tendency to add on a proton. This can be represented schematically by A B-j-H", where A and B are termed a conjugate or corresponding) acid-base pair. Before examining the consequences of this definition and its relation to more recent concepts we shall consider briefly the previous history of the terms acid and base . 

Click Chemistry Interactive for the self-study module acid-base conjugate pairs. 

Conjugates of nucleic acid related compounds (nucleobases, nucleosides and nucleotides) and calixarene scaffolds are potential candidates for the formation of well-defined supramolecular structures. Nucleobases are structurally predetermined to mediate non-covalent interactions, e.g. base pairing via hydrogen bonds and r-stacking to aromatic moieties. The versatile nature of the cahxarene corpus provides a convenient entry to multiple pre-oriented functionahties. By this combination a broad range of supramolecular architectures becomes accessible. Over the years a number of calixarene DNA hybrids have been constructed and investigated in their complexation properties towards nucleic acid related compounds. A valuable summary on this topic is given by Kumar et al. in Advances in Heterocyclic Chemistry [38]. 

Amines are organic bases whose acid—base chemistry is like that of ammonia. For example, methyl-amine behaves as a Bronsted base because the nonbonded electron pair of the nitrogen atom can accept a proton from an acid such as hydronium ion. When methylamine accepts a proton, the conjugate acid, methyl-ammonium ion, is produced. 

General acid catalysis is surely one of the best known catalytic processes in organic chemistry. Protonation enhances the electrophilic character of a molecule, leading to increased reactivity. Moreover, the formation of tight ion pairs or hydrogen-bonded complexes between a protonated reactant and the conjugate base of chiral acids has been a widely exploited method for enantioselective synthesis [71, 72]. 

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