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Ch.11 - Reactions of Alcohols
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.11 - Reactions of AlcoholsProblem 6d,e
Chapter 11, Problem 6d,e

Suggest the most appropriate method for each of the following laboratory syntheses. In each case, suggest both a chromium reagent and a chromium-free reagent.
(d) cyclopentanol → 1-ethylcyclopentanol (two steps)
(e) cyclopentylmethanol → 1-cyclopentylpropan-1-ol (two steps)

Verified step by step guidance
1
Step 1: For part (d), cyclopentanol → 1-ethylcyclopentanol, recognize that this transformation involves two steps: (1) oxidation of cyclopentanol to cyclopentanone and (2) addition of an ethyl group to the carbonyl carbon of cyclopentanone. Begin by selecting an appropriate chromium reagent for oxidation, such as Jones reagent (CrO3 in aqueous H2SO4) or PCC (pyridinium chlorochromate) for milder conditions. Alternatively, a chromium-free reagent like Dess-Martin periodinane or Swern oxidation can be used.
Step 2: For the second step of part (d), perform a nucleophilic addition of an ethyl group to the cyclopentanone. This can be achieved using an organometallic reagent like ethylmagnesium bromide (Grignard reagent) or ethyllithium. The reaction will yield 1-ethylcyclopentanol after protonation.
Step 3: For part (e), cyclopentylmethanol → 1-cyclopentylpropan-1-ol, recognize that this transformation involves two steps: (1) conversion of cyclopentylmethanol to cyclopentylmethanal (an aldehyde) and (2) chain elongation by two carbons to form the desired alcohol. Begin by oxidizing cyclopentylmethanol to cyclopentylmethanal using a chromium reagent like PCC or a chromium-free reagent like Dess-Martin periodinane.
Step 4: For the second step of part (e), perform a homologation reaction to elongate the chain. This can be achieved using a Wittig reaction to form an alkene intermediate, followed by hydroboration-oxidation to yield 1-cyclopentylpropan-1-ol. Alternatively, a Grignard reaction with ethylene oxide followed by protonation can also achieve the desired product.
Step 5: Summarize the reagents: For part (d), use a chromium reagent like PCC or a chromium-free reagent like Dess-Martin periodinane for oxidation, followed by ethylmagnesium bromide for nucleophilic addition. For part (e), use PCC or Dess-Martin periodinane for oxidation, followed by a homologation reaction (e.g., Wittig reaction and hydroboration-oxidation or Grignard reaction with ethylene oxide).

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Key Concepts

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

Reagents in Organic Synthesis

Reagents are substances used in chemical reactions to facilitate the transformation of reactants into products. In organic synthesis, choosing the right reagent is crucial for achieving the desired product efficiently and selectively. Chromium reagents, such as chromic acid, are often used for oxidation reactions, while chromium-free alternatives, like PCC (pyridinium chlorochromate), provide similar reactivity without the environmental concerns associated with chromium.
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Functional Group Transformation

Functional group transformation involves changing one functional group into another during a chemical reaction. In the context of the question, converting cyclopentanol to 1-ethylcyclopentanol requires the introduction of an ethyl group, which can be achieved through alkylation reactions. Understanding how to manipulate functional groups is essential for designing synthetic pathways in organic chemistry.
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Multi-step Synthesis

Multi-step synthesis refers to a series of chemical reactions that convert starting materials into a final product through intermediate compounds. Each step must be carefully planned to ensure that the desired transformations occur efficiently. In the examples provided, synthesizing 1-ethylcyclopentanol and 1-cyclopentylpropan-1-ol involves strategic selection of reagents and conditions to achieve the final products in two steps.
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Related Practice
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Suggest the most appropriate method for each of the following laboratory syntheses. In each case, suggest both a chromium reagent and a chromium-free reagent.

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Textbook Question

Predict the products you expect when the following starting material undergoes oxidation with an excess of each of the reagents shown below.

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