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Chapter 11: Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations: 11-3 Characteristics of the Reaction Book Title: Organic Chemistry Printed By: Joetta Lloyd (jllo8980@students.vsu.edu) © 2016 Cengage Learning, Cengage Learning

11-3 Characteristics of the Reaction

Now that we know how reactions occur, we need to see how they can be used and what variables affect them. Some reactions are fast, and some are slow; some take place in high yield and others in low yield. Understanding the factors involved can be of tremendous value. Let’s begin by recalling a few things about reaction rates in general.

The rate of a chemical reaction is determined by the activation energy , the energy difference between reactant ground state and transition state. A change in reaction conditions can affect either by changing the reactant energy level or by changing the transition-state energy level. Lowering the reactant energy or raising the transition-state energy increases and decreases the reaction rate; raising the reactant energy or decreasing the transition-state energy decreases and increases the reaction rate (Figure 11-5). We’ll see examples of all these effects as we look at reaction variables.

Figure 11-5

The effects of changes in reactant and transition-state energy levels on reaction rate. (a) A higher reactant energy level (red curve) corresponds to a faster reaction (smaller ). (b) A higher transition-state energy level (red curve) corresponds to a slower reaction (larger ).

Chapter 11: Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations: 11-3 Characteristics of the Reaction Book Title: Organic Chemistry Printed By: Joetta Lloyd (jllo8980@students.vsu.edu) © 2016 Cengage Learning, Cengage Learning

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