Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics

Problem 51b

Chapter 4, Problem 51b

For each set of reactive intermediates, rank them in order of reactivity (1 = most reactive).
(b)

Verified step by step guidance

Step 1: Identify the reactive intermediates shown in the image. These include radicals, carbocations, and carbanions. Each structure has a specific type of reactive intermediate based on the presence of a lone electron, positive charge, or negative charge.

Step 2: Understand the factors that influence the stability and reactivity of these intermediates. For radicals, carbocations, and carbanions, stability is influenced by factors such as hyperconjugation, resonance, and inductive effects. Generally, more stable intermediates are less reactive.

Step 3: Analyze the structures provided. Look for stabilizing features such as alkyl groups (which provide hyperconjugation and inductive effects), resonance stabilization (delocalization of charge or lone electron), and whether the intermediate is primary, secondary, or tertiary.

Step 4: Rank the intermediates based on their stability. For example, tertiary carbocations are more stable than secondary or primary carbocations due to greater hyperconjugation and inductive effects. Similarly, radicals and carbanions follow similar trends in stability.

Step 5: Assign the reactivity ranking (1 = most reactive) based on the inverse relationship between stability and reactivity. The least stable intermediate will be the most reactive, and the most stable intermediate will be the least reactive.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reactive Intermediates

Reactive intermediates are transient species that form during the course of a chemical reaction. They include carbocations, carbanions, and free radicals, each with distinct stability and reactivity. Understanding their structure and stability is crucial, as more stable intermediates are generally less reactive, while less stable ones are more reactive.

Stability of Intermediates

The stability of reactive intermediates is influenced by factors such as hybridization, resonance, and inductive effects. For example, tertiary carbocations are more stable than primary ones due to hyperconjugation and inductive effects from surrounding alkyl groups. Recognizing these stability trends helps in predicting the reactivity of different intermediates.

Reactivity Trends

Reactivity trends in organic chemistry often follow the principle that less stable intermediates are more reactive. This is due to their higher energy state, which drives them to react quickly to achieve a more stable configuration. Understanding these trends allows chemists to rank intermediates based on their expected reactivity in a given reaction.

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Textbook Question

For each set of reactive intermediates, rank them in order of reactivity (1 = most reactive).

(a)

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Textbook Question

The A value of a substituent on a cyclohexane ring is essentially the ∆G° for a substituent going from the equatorial to the axial position in a chair–chair interconversion. Because most substituents prefer to be in the equatorial position, A values are, by definition, positive numbers. Use the table of A values to calculate ∆G° and K_eq for the chair–chair interconversions shown.

(c)

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Textbook Question

Predict the product(s) of the following halogenation reactions. Only one equivalent of the halogen is used in each case. If the reaction proceeds selectively, indicate this by only drawing the major product. If the reaction is not selective, draw all possible products.

(e)

(d)

For each set of reactive intermediates, rank them in order of reactivity (1 = most reactive).

(c)

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