Orgo Final (Ethers and Epoxides)

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Last updated 2:14 PM on 4/25/26
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11 Terms

1
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Williamson-Ether Synthesis

#1 Preparation of Ethers - ___________

  • Step 1: Acid-Base Reaction

  • Step 2: SN2 Reaction (fails with tertiary alkyl halides)

    • Original stereochemistry of the alcohol is MAINTAINED

<p><strong>#1 Preparation of Ethers - ___________</strong></p><ul><li><p><strong>Step 1:</strong> Acid-Base Reaction</p></li><li><p><strong>Step 2:</strong> SN2 Reaction (fails with tertiary alkyl halides) </p><ul><li><p><span style="color: green;"><strong>Original stereochemistry of the alcohol is MAINTAINED </strong></span></p></li></ul></li></ul><p></p>
2
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Acid-Catalyzed Addition of Alcohols to Alkenes

#2 Preparation of Ethers - _____________

  • An alcohol can add to an alkene in the presence of an acid-catalyst

  • Carbocation Intermediate so shifts are possible.

<p><strong>#2 Preparation of Ethers - _____________</strong></p><ul><li><p>An alcohol can add to an alkene in the presence of an acid-catalyst </p></li><li><p><span style="color: blue;"><strong>Carbocation Intermediate so shifts are possible. </strong></span></p></li></ul><p></p>
3
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Acid-Catalyzed Cleavage by HX

#3 Reactions of Ethers- __________

  • Reaction requires both a strong acid and a strong nucleophile

    • HBr and HI are used

  • Mechanism (Sn1 or Sn2) depends on the substitution of the alkyl group

  • Aryl and Vinylic ethers will NOT be cleaved

  • Split across the O and insert the halide

<p><strong>#3 Reactions of Ethers- __________</strong></p><ul><li><p>Reaction requires both a strong acid and a strong nucleophile </p><ul><li><p><strong>HBr </strong>and <strong>HI </strong>are used</p></li></ul></li><li><p><span style="color: red;"><strong>Mechanism (Sn1 or Sn2) depends on the substitution of the alkyl group</strong></span></p></li><li><p>Aryl and Vinylic ethers will NOT be cleaved </p></li><li><p><span style="color: green;"><strong><u>Split across the O and insert the halide </u></strong></span></p></li></ul><p></p>
4
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Acid-Catalyzed Cleavage by HX

#3 Example 2

<p>#3 Example 2 </p>
5
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Peroxycarboxylic Acids

#4 Epoxide Formation: __________

  • mCPBA

  • Mechanism is concerted

  • The reaction is stereospecific - Syn Addition

  • The original stereochemistry of the alkene is maintained

    • A cis alkene will yield a cis epoxide

<p><strong>#4 Epoxide Formation: __________</strong></p><ul><li><p><mark data-color="yellow" style="background-color: yellow; color: inherit;">mCPBA</mark></p></li><li><p>Mechanism is <span style="color: red;"><strong>concerted </strong></span></p></li><li><p>The reaction is <strong><mark data-color="green" style="background-color: green; color: inherit;">stereospecific - Syn Addition</mark></strong></p></li><li><p><strong>The original stereochemistry of the alkene is maintained </strong></p><ul><li><p>A cis alkene will yield a cis epoxide </p></li></ul></li></ul><p></p>
6
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Peroxycarboxylic Acids

#4 Example 2

<p>#4 Example 2 </p>
7
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Internal Nucleophilic Substitution in Halohydrins

#5 Epoxide Formation: __________

  • A base is used to deprotonate the alcohols, which allows for the intramolecular SN2 reaction

    • Intramolecular variation of Williamson Ether Synthesis

<p><strong>#5 Epoxide Formation: __________</strong></p><ul><li><p>A <span style="color: purple;"><strong>base is used to deprotonate the alcohols</strong></span>, which allows for the <strong>intramolecular SN2 reaction </strong></p><ul><li><p>Intramolecular variation of <strong>Williamson Ether Synthesis </strong></p></li></ul></li></ul><p></p>
8
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Acid-Catalyzed Ring Opening

#6 Reactions of Epoxides: __________

  • An acid catalyst is used when the nucleophile is weak

  • Opens the epoxide on the MORE substituted side (regioselective)

  • Selectivity: ANTI ADDITION

    • Protonate

    • Attack

    • Deprotonate

<p><strong>#6 Reactions of Epoxides: __________</strong></p><ul><li><p>An acid catalyst is used when the <strong>nucleophile is weak </strong></p></li><li><p><span style="color: blue;"><strong><em><mark data-color="yellow" style="background-color: yellow; color: inherit;">Opens the epoxide on the MORE substituted side (regioselective)</mark></em></strong></span></p></li><li><p>Selectivity: <span style="color: red;"><strong>ANTI ADDITION</strong></span></p><ul><li><p><strong>Protonate </strong></p></li><li><p><strong>Attack </strong></p></li><li><p><strong>Deprotonate </strong></p></li></ul></li></ul><p></p>
9
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Acid-Catalyzed Ring Opening

#6 Example 2

<p>#6 Example 2 </p>
10
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Nucleophilic Ring Opening

#7) Reactions of Epoxides: __________

  • Strong Nucleophiles do not require an acid catalyst

  • Opens the epoxide on the less-substituted side (regioselective)

  • Stereoselectivity: Anti-Addition

    • Attack

    • Protonate

Some instances require a workup step

<p><strong>#7) Reactions of Epoxides: __________</strong></p><ul><li><p>Strong Nucleophiles do not require an acid catalyst </p></li><li><p><span style="color: blue;"><strong><em><mark data-color="yellow" style="background-color: yellow; color: inherit;">Opens the epoxide on the less-substituted side (regioselective) </mark></em></strong></span></p></li><li><p>Stereoselectivity: <span style="color: red;"><strong>Anti-Addition</strong></span></p><ul><li><p>Attack </p></li><li><p>Protonate </p></li></ul></li></ul><p>Some instances require a workup step</p>
11
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Nucleophilic Ring Opening

#7 Example 2

<p>#7 Example 2 </p>