Textbook Question
a. Name the kind of sigmatropic rearrangement that occurs in each of the following reactions.
3.
16. Conjugated Systems
Sigmatropic Rearrangement
4:08 minutesProblem 14
Textbook Question
Why was a deuterated compound used in the last reaction on the preceding page?
Verified step by step guidance1
The reaction shown involves a thermal rearrangement of a cyclic compound. The use of a deuterated compound (CD2) is significant because deuterium (D) is an isotope of hydrogen and can be tracked during the reaction due to its distinct mass and spectroscopic properties.
Deuterium is used to study reaction mechanisms. In this case, it helps to determine whether the hydrogen atoms are retained in their original positions or if they migrate during the rearrangement process.
The arrows in the starting material indicate the movement of electrons during the reaction. This suggests a pericyclic reaction mechanism, likely a [1,5]-sigmatropic shift, where the hydrogen or deuterium migrates across the molecule.
By using deuterium, researchers can confirm the migration pathway and ensure that the observed product matches the expected mechanism. The presence of CD2H in the product indicates that one deuterium atom has migrated while the other remains in its original position.
This experimental design provides evidence for the reaction mechanism and validates theoretical predictions about the behavior of hydrogen and deuterium in pericyclic reactions.
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4mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Deuterated Compounds
Deuterated compounds are molecules in which one or more hydrogen atoms are replaced with deuterium, a stable isotope of hydrogen. This substitution can affect the physical and chemical properties of the compound, such as its reactivity and stability. In reactions, deuterated compounds can serve as tracers to study reaction mechanisms or to determine the position of hydrogen atoms in the product.
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Sigmatropic Rearrangement
Sigmatropic rearrangements are a class of pericyclic reactions where a sigma bond and a pi bond undergo a concerted rearrangement. These reactions often involve the migration of a substituent across a conjugated system, leading to the formation of new bonds. The use of deuterated compounds in these reactions can help elucidate the mechanism by tracking the movement of deuterium during the rearrangement.
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Reaction Mechanism Analysis
Analyzing reaction mechanisms involves understanding the step-by-step process by which reactants transform into products. This includes identifying intermediates, transition states, and the role of catalysts or solvents. In the context of using deuterated compounds, mechanistic studies can reveal how the presence of deuterium influences the reaction pathway and the stability of intermediates, providing insights into the fundamental principles of organic chemistry.
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