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Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen
McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoMcMurry 8th EditionCh.14 Some Compounds with Oxygen, Sulfur, or a HalogenProblema 74
Capitolo 14, Problema 74

Using the alcohol shown, draw all the possible alkenes that might be formed on its dehydration. Which do you think will be the major product(s)? Which do you think will be the minor product(s)? It is alright to have more than one major and minor product.

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Identify the alcohol functional group in the given molecule. Dehydration of alcohols involves the removal of a water molecule (H₂O), which consists of a hydroxyl group (-OH) and a hydrogen atom from an adjacent carbon atom.
Determine all possible β-hydrogens (hydrogens on carbons adjacent to the carbon bearing the -OH group). Each β-hydrogen can lead to a different alkene product when eliminated.
Apply the E1 (unimolecular elimination) mechanism, which is typical for dehydration of alcohols under acidic conditions. The steps include: (1) protonation of the -OH group to form a better leaving group (H₂O), (2) loss of H₂O to form a carbocation intermediate, and (3) elimination of a β-hydrogen to form an alkene.
Consider carbocation rearrangements if applicable. If the initial carbocation can rearrange to a more stable carbocation (e.g., via hydride or alkyl shifts), this rearrangement will occur before elimination, leading to additional alkene products.
Use Zaitsev's rule to predict the major and minor products. Zaitsev's rule states that the more substituted alkene (the one with more alkyl groups attached to the double-bonded carbons) is generally the major product, while less substituted alkenes are minor products. Draw all possible alkenes and classify them accordingly.

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Dehydration Reaction

A dehydration reaction involves the removal of a water molecule from an alcohol, leading to the formation of an alkene. This process typically occurs under acidic conditions, where the alcohol is protonated to form a better leaving group. The resulting carbocation can rearrange or lose a proton to form the double bond characteristic of alkenes.
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Percorso guidato
1:30
Alcohol Reactions: Dehydration Reactions Concept 1

Zaitsev's Rule

Zaitsev's Rule states that in elimination reactions, the more substituted alkene is generally the major product. This is because more substituted alkenes are more stable due to hyperconjugation and the inductive effect. Understanding this rule helps predict which alkenes will be favored in the dehydration of alcohols.
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Percorso guidato
1:24
Zaitsev’s Rule Concept 2

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others. In the context of dehydration, different alkenes can form depending on the position of the double bond. Analyzing the possible products and their stability allows chemists to determine which will be major or minor products based on their regioselectivity.
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