Intermediate

Definition

An intermediate is a chemical species that is formed during the course of a chemical reaction, existing temporarily between the reactants and the final products. Intermediates play a crucial role in understanding the mechanisms and energetics of chemical transformations, particularly in the context of organic chemistry topics such as reaction energy diagrams, electrophilic addition reactions, and halohydrin formation.

5 Must Know Facts For Your Next Test

1. Intermediates are often represented as high-energy species in reaction energy diagrams, with the transition state being the highest-energy point along the reaction coordinate.
2. In electrophilic addition reactions of alkenes, the formation of a carbocation intermediate is a key step that determines the overall regiochemistry and stereochemistry of the addition.
3. The addition of a halogen (HO-X) to an alkene to form a halohydrin involves the formation of a cyclic bromonium ion intermediate, which is subsequently opened by water to yield the final product.
4. The stability and reactivity of intermediates can have a significant impact on the overall rate and mechanism of a chemical reaction.
5. Understanding the nature and behavior of intermediates is crucial for predicting the outcomes of organic reactions and designing new synthetic strategies.

Review Questions

• Explain the role of intermediates in the context of reaction energy diagrams and transition states.
  • Intermediates are the chemical species that are formed during the course of a reaction, existing temporarily between the reactants and the final products. In the context of reaction energy diagrams, intermediates are often represented as high-energy species, with the transition state being the highest-energy point along the reaction coordinate. The formation and consumption of intermediates are key steps in the overall reaction mechanism, and their stability and reactivity can have a significant impact on the energetics and kinetics of the transformation.
• Describe the role of intermediates in electrophilic addition reactions of alkenes.
  • In electrophilic addition reactions of alkenes, the formation of a carbocation intermediate is a crucial step that determines the overall regiochemistry and stereochemistry of the addition. The electrophile first attacks the alkene, forming a planar carbocation intermediate. The stability and reactivity of this intermediate then guide the subsequent addition of the nucleophile, leading to the final product. Understanding the nature and behavior of these carbocation intermediates is essential for predicting and controlling the outcomes of electrophilic addition reactions.
• Analyze the role of intermediates in the formation of halohydrins from alkenes through the addition of HO-X.
  • The addition of a halogen (HO-X) to an alkene to form a halohydrin involves the formation of a cyclic bromonium ion intermediate. This intermediate is then opened by water, with the hydroxyl group and the halogen atom adding to the alkene in a regio- and stereospecific manner. The stability and reactivity of the bromonium ion intermediate are key factors that influence the overall mechanism and the final product distribution. Recognizing the importance of this intermediate and understanding its behavior is crucial for predicting and controlling the outcomes of halohydrin formation reactions.

Related terms

Transition State: The transition state is the highest-energy intermediate along the reaction coordinate, representing the point at which the reactants are being converted into the products.

Reaction Mechanism: The step-by-step sequence of elementary steps that describe how a chemical reaction proceeds, often involving the formation and consumption of intermediates.

Kinetics: The study of the rates of chemical reactions and the factors that influence them, including the formation and consumption of intermediates.