Double-Replacement Molecule-Formation Reactions

A central issue in making chemistry greener is the efficiency of incorporating the reactant atoms into the product compound. Any atoms that are used in the reaction but are not part of the product are wasted, and this waste must subsequently be disposed of. If chemists can design reactions that do not have wasted atoms, there are no disposal issues and no potential for environmental impact. This type of efficiency can be measured in terms of percentage atom utilization  

Green chemists continue to work on methods of making product compounds that use aU of the reactant atoms. The conventional and net ionic equations for these reactions are usually classified as combination reactions, which were first introduced in Section 8.6. Research on safer chemicals, better reaction conditions, and more efficient reaction pathways continues to make chemical manufacturing more healthful for humans and more friendly to the environment. 

9 Given reactants that yield a molecular product, write the net ionic equation. 

The reaction of an acid often leads to an ion combination that yields a molecular product instead of a precipitate. Except for the difference in the product, the equations are written in exactly the same way. Just as you had to recognize an insoluble product and not break it up in total ionic equations, you must now recognize a molecular product and not break it into ions. Water and weak acids are the two kinds of molecular products you will find. 

Neutralization reactions are the most common molecular-product reactions. 

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Section 9.8 Double-Replacement Molecule-Formation Reactions... 

Many addition-elimination reactions at carbonyl centers involve a nucleophilic attack on the carbonyl carbon, followed by an elimination that restores the double bond. We first explore addition followed by 1,2-elimination, one of many types of reactions referred to as condensations. Strictly speaking, a condensation occurs when two large molecules combine to create a more complex molecule with the loss of a small molecule, such as water or an alcohol. Therefore, a condensation is a form of substitution. We will also examine condensation reactions that form polymers (see Chapter 13). One of the more complex condensations is the formation of an imine or enamine from a carbonyl and an amine. In both of these cases an oxygen is replaced by a nitrogen with loss of water (Eq 10.105 and 10.106). 

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