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Ch.4 - The Study of Chemical Reactions
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.4 - The Study of Chemical ReactionsProblem 30
Chapter 4, Problem 30

Rank the following radicals in decreasing order of stability. Classify each as primary, secondary, or tertiary.
a. The isopentyl radical, Structural formula of the 2-methyl-2-butyl radical, showing its carbon and hydrogen arrangement.
b. The 3-methyl-2-butyl radical, Structural formula of the 2-methyl-2-butyl radical, showing its carbon and hydrogen arrangement.
c. The 2-methyl-2-butyl radical, Structural formula of the 2-methyl-2-butyl radical, showing its carbon and hydrogen arrangement.
d. Chemical structure of a radical, showing a hexagonal ring with a substituent, representing radical stability concepts.

Verified step by step guidance
1
Step 1: Identify the type of radical (primary, secondary, or tertiary) for each structure. A primary radical is attached to one carbon, a secondary radical is attached to two carbons, and a tertiary radical is attached to three carbons.
Step 2: Analyze the stability of each radical. Radical stability increases in the order: primary < secondary < tertiary. This is due to hyperconjugation and inductive effects from neighboring alkyl groups.
Step 3: For the isopentyl radical ((CH3)2CHCH2-CH2•), classify it as a primary radical because the unpaired electron is on a carbon attached to only one other carbon.
Step 4: For the 3-methyl-2-butyl radical (CH3-CH•-CH(CH3)2), classify it as a secondary radical because the unpaired electron is on a carbon attached to two other carbons.
Step 5: For the 2-methyl-2-butyl radical (CH3-C•(CH3)CH2CH3), classify it as a tertiary radical because the unpaired electron is on a carbon attached to three other carbons. For the cyclohexyl radical, classify it as a secondary radical because the unpaired electron is on a carbon attached to two other carbons in the ring.

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Key Concepts

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

Radical Stability

Radical stability refers to the relative stability of free radicals, which are species with unpaired electrons. The stability of a radical is influenced by the degree of substitution on the carbon atom bearing the unpaired electron. Generally, tertiary radicals are more stable than secondary radicals, which are more stable than primary radicals due to hyperconjugation and the inductive effect of alkyl groups.
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The radical stability trend.

Degree of Substitution

The degree of substitution indicates how many alkyl groups are attached to the carbon atom that holds the radical. A primary radical has one alkyl group, a secondary radical has two, and a tertiary radical has three. The more alkyl groups attached, the greater the stabilization of the radical due to hyperconjugation, which involves the overlap of σ-bonds with the empty p-orbital of the radical.
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Nucleophiles and Electrophiles can react in Substitution Reactions.

Hyperconjugation

Hyperconjugation is a stabilizing interaction that occurs when the electrons in a σ-bond (usually C-H or C-C) interact with an adjacent empty p-orbital, such as that of a radical. This interaction allows for the delocalization of electrons, which helps to stabilize the radical. The more hyperconjugative interactions available, the more stable the radical becomes, making tertiary radicals the most stable due to their greater number of adjacent alkyl groups.
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Understanding trends of alkene stability.
Related Practice
Textbook Question

In the presence of a small amount of bromine, cyclohexene undergoes the following light-promoted reaction:

b. Draw the structure of the rate-limiting transition state.

c. Use Hammond's postulate to predict which intermediate most closely resembles this transition state.

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Textbook Question

Write an equation for the reaction of vitamin E with an oxidizing radical (RO•) to give ROH and a less reactive free radical.

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Textbook Question

The triphenylmethyl cation is so stable that some of its salts can be stored for months. Explain why this cation is so stable.

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Textbook Question

Acetonitrile (CH3C≡N) is deprotonated by very strong bases. Write resonance forms to show the stabilization of the carbanion that results.

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Textbook Question

When it is strongly heated, ethyl diazoacetate decomposes to give nitrogen gas and a carbene. Draw a Lewis structure of the carbene.

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Textbook Question

Acetylacetone (pentane-2,4-dione) reacts with sodium hydroxide to give water and the sodium salt of a carbanion. Write a complete structural formula for the carbanion, and use resonance forms to show the stabilization of the carbanion.

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