Predicting the Products of a Reaction

Before you can balance a chemical equation, you have to know the formulas for all the reactants and products. If the names are given for these substances, you have to know how to write formulas from the names (Chap. 6). If only reactants are given, you have to know how to predict the products from the reactants. This latter topic is the subject of this section. 

To simplify the discussion, we will classify simple chemical reactions into five types Type 1 combination reactions Type 4 double-substitution reactions 

Type 2 decomposition reactions Type 3 substitution reactions 

More complex oxidation-reduction reactions will be discussed in Chap. 14. 

A combination reaction is a reaction of two reactants to produce one product. The simplest combination reactions are the reactions of two elements to form a compound. After all, if two elements are treated with each other, they can either react or not. There generally is no other possibility, since neither can decompose. In most reactions like this, there will be a reaction. The main problem is to write the formula of the product correctly and then to balance the equation. In this process, first determine the formula of the product from the rules of chemical combination (Chap. 5). Only after the formulas of the reactants and products have all been written down, balance the equation by adjusting the coefficients. 

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Strategy When predicting the product of a reaction, you have to recall what you know about the kind of reaction being carried out and then apply that knowledge to the specific case you re dealing with. In the present instance, recall that the two methods of... 

Substitution and elimination reactions are almost always in competition with each other. In order to predict the products of a reaction, you must determine which mechanism(s) win the competition. In some cases, there is one clear winner. For example, consider a case in which a tertiary alkyl halide is treated with a strong base, such as hydroxide ... 

In order to predict the products of a reaction, the first step is determining the identity and nature of the reagent. That is, you must analyze the reagent and determine the category to which it belongs. Let s get some practice with this critical skill. 

The values of reaction enthalpies in a forward search can be of use in predicting the products of a reaction the more exothermic a reaction, the more it should be preferred. The situation will be different in a retrosynthetic search where retroreactions should be calculated to be endothermic to some degree. This underlines the point previously made (Sect. 2, Fig. 9) that the differences between a forward and a retrosynthetic search do not reside in the way reactions are generated — in both cases in EROS by the formal reaction schemes — but in the way they are evaluated. 

In the last several chapters, we saw the power of mechanisms in explaining the re-giochemistry and stereochemistry of every reaction. A solid understanding of these concepts gives us the power to predict the products of a reaction. That is the subject of this chapter. 

This situation illustrates why there are cases where it is often difficult to predict the products of a reaction with certainty. Catalysts for the reduction include Ag+, Mn2+, V205, and peroxides. 

Understand how to use solubility rules to predict the products of a reaction and write net ionic equations. 

In Chapter 7, we learned how to do nnmerical calculations for compounds, using their formulas as a basis. This chapter lays the foundation for doing similar calculations for chemical reactions, using the balanced equation as a basis. The chemical equation is introduced in Section 8.1, and methods for balancing equations are presented in Section 8.2. To write equations, we must often be able to predict the products of a reaction from a knowledge of the properties of the reactants. Section 8.3 shows how to classify chemical reactions into types to predict the products of thousands of reactions. An important type of reaction— the acid-base reaction— is discussed in Section 8.4. 

Balancing Simple Equations Predicting the Products of a Reaction... 

The identity of products and reactants must he specified using chemical symbols. In some cases it is possible to predict the products of a reaction. More often, the reactants and products must be verified by chemical analysis. (Generally, you will be given information regarding the identity of the reactants and products.)... 

Knowing something about the structure of a transition state is important when you are trying to predict the products of a reaction. In Section 3.7, you saw that the structure of the transition state lies between the structure of the reactants and the structure of the products. But what do we mean by between Does the structure of the transition state lie exactly halfway between the structures of the reactants and products (as in II in the following diagram), or does it resemble the reactants more closely than it resembles the products (as in I), or is it more like the products than the reactants (as in III) ... 

Predict the products of a reaction between hexanoic acid and trimethylamine done at room temperature. 

Many addition reactions have been covered in this chapter, and in each case, there are several factors to take into account when predicting the products of a reaction. Let s now summarize the factors that are common to all addition reactions In order to predict products properly, the following three questions must be considered ... 

What the question asks seems straightforward Predict the product of a reaction of the type we have seen several times, going back to Chapters 6 and 7. Although this problem does not ask explicitly how or why —which are our clues to thinking about mechanisms—you know that haloalkanes may transform by a variety of pathways under the given conditions. Hence, mechanistic thinking is of the essence. 

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