Acid-base reactions curved arrows

In Section 1 9 we introduced curved arrows as a tool to systematically generate resonance structures by moving electrons The mam use of curved arrows however is to show the bonding changes that take place in chemical reactions The acid-base reactions to be discussed in Sections 1 12-1 17 furnish numer ous examples of this and deserve some preliminary comment... 

Wnte an equation for the Brpnsted acid-base reaction that occurs when each of the fol lowing acids reacts with water Show all unshared electron pairs and formal charges and use curved arrows to track electron movement... 

Look closely at the acid-base reaction in Figure 2.5, and note how it is shown. Dimethyl ether, the Lewis base, donates an electron pair to a vacant valence orbital of the boron atom in BF3, a Lewis acid. The direction of electron-pair flow from the base to acid is shown using curved arrows, just as the direction of electron flow in going from one resonance structure to another was shown using curved arrows in Section 2.5. A cuived arrow always means that a pair of electrons moves from the atom at the tail of the arrow to the atom at the head of the arrow. We ll use this curved-arrow notation throughout the remainder of this text to indicate electron flow during reactions. 

Predict the structure of the product formed in the reaction of the organic base pyridine with the organic acid acetic acid, and use curved arrows to indicate the direction of electron flow. 

The reaction of PC14+ with Cl- is a Lewis acid-base reaction. Draw electron-dot structures for the reactants and products, and use the curved arrow notation (Section 15.16) to represent the donation of a lone pair of electrons from the Lewis base to the Lewis acid. 

The Br0nsted-Lowry definition of acids and bases depends on the transfer of a proton from the acid to the base. The base uses a pair of nonbonding electrons to form a bond to the proton. G. N. Lewis reasoned that this kind of reaction does not need a proton. Instead, a base could use its lone pair of electrons to bond to some other electron-deficient atom. In effect, we can look at an acid-base reaction from the viewpoint of the bonds that are formed and broken rather than a proton that is transferred. The following reaction shows the proton transfer, with emphasis on the bonds being broken and formed. Organic chemists routinely use curved arrows to show the movement of the participating electrons. 

The Lewis acid-base definitions include reactions having nothing to do with protons. Following are some examples of Lewis acid-base reactions. Notice that the common Br0nsted-Lowry acids and bases also fall under the Lewis definition, with a proton serving as the electrophile. Curved arrows (red) are used to show the movement of electrons, generally from the nucleophile to the electrophile. 

Identify nucleophiles (Lewis bases) and electrophiles (Lewis acids), and write equations for Lewis acid-base reactions using curved arrows to show the flow of electrons. 

Label the reactants in these acid-base reactions as Lewis acids (electrophiles) or Lewis bases (nucleophiles). Use curved arrows to show the movement of electron pairs in the reactions. 

Problem 2.25 For each reaction, label the Lewis acid and base. Use curved arrow notation to show the movement of electron pairs. 

Because the.se substitution reactions involve electron-rich nucleophiles, they are called nucleophilic substitution reactions. Examples are shown in Equations [l]-[3]. Nucleophilic substitutions are Lewis acid—base reactions. The nucleophile donates its electron pair, the alkyl halide (Lewis acid) accepts it, and the C-X bond is heterolytically cleaved. Curved arrow notation can be used to show the movement of electron pairs, as shown in Equation [3]. 

Transition-state representations are shown for two acid-base reactions. Por each one, write the equation for the reaction it represents in the direction for which the equilibrium lies to the right. Label the acid, the base, the conjugate acid, and the conjugate base, and use curved arrows to show the flow of electrons. 

Acid-base reactions are simple fundamental reactions that will enable you to see how chemists use curved arrows to represent mechanisms of reactions and how they depict the processes of bond breaking and bond making that occur as molecules react. 

The following acid-base reactions give other examples of the use of the curved-arrow notation ... 

Write an equation, using the curved-arrow notation, for the acid—base reaction that will take place when each of the following are mixed. If no appreciable acid—base reaction takes place, because the equilibrium is unfavorable, you should so indicate. 

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