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Questions and Answers
What is a characteristic of dissolving metal reductions?
What is a characteristic of dissolving metal reductions?
Lindlar's catalyst converts alkynes to alkenes in a stereoselective manner.
Lindlar's catalyst converts alkynes to alkenes in a stereoselective manner.
True
What are common reducing agents that contain a hydrogen atom bonded to boron or aluminum?
What are common reducing agents that contain a hydrogen atom bonded to boron or aluminum?
sodium borohydride and lithium aluminum hydride
The addition of H2 in catalytic hydrogenation requires the presence of a ________ catalyst.
The addition of H2 in catalytic hydrogenation requires the presence of a ________ catalyst.
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Match the following reducing methods with their characteristics:
Match the following reducing methods with their characteristics:
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Which of the following best describes an oxidizing agent?
Which of the following best describes an oxidizing agent?
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Stereoselectivity in reduction reactions does not influence the arrangement of atoms or groups in the product.
Stereoselectivity in reduction reactions does not influence the arrangement of atoms or groups in the product.
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Which statement describes the heat of hydrogenation ( ext{ΔHo}) of alkenes?
Which statement describes the heat of hydrogenation ( ext{ΔHo}) of alkenes?
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What type of reaction occurs when converting an alkyne to an alkene?
What type of reaction occurs when converting an alkyne to an alkene?
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Lindlar's catalyst can fully hydrogenate alkynes to alkanes.
Lindlar's catalyst can fully hydrogenate alkynes to alkanes.
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What effect does the hydrogenation of unsaturated vegetable oil have on its melting point?
What effect does the hydrogenation of unsaturated vegetable oil have on its melting point?
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Lindlar’s catalyst is a less active form of __________ that allows for selective hydrogenation.
Lindlar’s catalyst is a less active form of __________ that allows for selective hydrogenation.
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Match the following concepts with their descriptions:
Match the following concepts with their descriptions:
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What is the primary function of Lindlar's catalyst in alkyne reduction?
What is the primary function of Lindlar's catalyst in alkyne reduction?
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Hydroboration-acidification can be used to obtain a trans alkene from an alkyne.
Hydroboration-acidification can be used to obtain a trans alkene from an alkyne.
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When hydrogenating alkenes that yield the same alkane, the alkene with the __________ heat of hydrogenation is more stable.
When hydrogenating alkenes that yield the same alkane, the alkene with the __________ heat of hydrogenation is more stable.
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What type of product is exclusively formed when performing a dissolving metal reduction of an alkyne?
What type of product is exclusively formed when performing a dissolving metal reduction of an alkyne?
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Dissolving metal reductions yield the less stable cis product preferentially.
Dissolving metal reductions yield the less stable cis product preferentially.
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What are the two categories of oxidizing agents?
What are the two categories of oxidizing agents?
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Reduction of alkyl halides to alkanes typically uses ______ as a reductant.
Reduction of alkyl halides to alkanes typically uses ______ as a reductant.
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Match the following oxidizing agents with their characteristics:
Match the following oxidizing agents with their characteristics:
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In the context of alkyne reduction, what is the role of Na in NH3 during dissolving metal reduction?
In the context of alkyne reduction, what is the role of Na in NH3 during dissolving metal reduction?
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The anti addition of hydrogen occurs during the formation of the trans alkene in alkyne reduction.
The anti addition of hydrogen occurs during the formation of the trans alkene in alkyne reduction.
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What mechanism is followed during the reduction of polar C—X σ bonds?
What mechanism is followed during the reduction of polar C—X σ bonds?
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Study Notes
Advanced Organic Chemistry - Chapter 1, Part B - MSC Students
- Course title: Advanced Organic Chemistry
- Specific part of course: Chapter 1, Part B
- Target audience: MSC Students
- Instructor: Dima Sabbah, Ph.D.
- Academic term: Fall 2014
Oxidation and Reduction - Introduction
- Oxidation increases the number of bonds between carbon and a more electronegative atom (usually C-O) or decreases the number of C-H bonds.
- Reduction decreases the number of C-Z bonds (usually C-O) or increases the number of C-H bonds.
Oxidation and Reduction - Reducing Agents
- Three ways to introduce 2 hydrogens (Hs) during a reduction:
- First method uses H2 gas (catalytic hydrogenation) with a metal catalyst (Pt, Pd, or Ni).
- Second method adds two protons (2H+) and two electrons (2e-) to a substrate (2H+ + 2e- = H2). Uses alkali metals as a source of electrons (e.g., Na° in liquid ammonia) and liquid ammonia as a proton source. This is known as dissolving metal reduction.
- Third method adds a hydride (H-) and a proton (H+). Common hydride reducing agents have hydrogen bonded to boron or aluminum (e.g., sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4)).
Oxidation and Reduction - Reduction of Alkenes: Catalytic Hydrogenation
- Addition of H2 to alkenes occurs only in the presence of a metal catalyst (usually Pd, Pt, or Ni) adsorbed onto a finely divided inert solid, such as charcoal. This is called catalytic hydrogenation.
- Hydrogen adds in a syn fashion.
- The heat of hydrogenation (ΔH°) can be used to measure the relative stability of alkenes. The more stable alkene has the lower heat of hydrogenation.
- The mechanism involves complexation of H2 and the alkene with the catalyst, followed by sequential addition of H atoms.
Oxidation and Reduction - Reduction of Alkynes
- Three methods of adding H2 to a triple bond.
- Adding two equivalents of H2 forms an alkane.
- Adding one equivalent of H2 in a syn fashion forms a cis alkene.
- Adding one equivalent of H2 in an anti fashion forms a trans alkene.
Oxidation and Reduction - Alkyne reduction to a Cis Alkene
- Palladium metal is too reactive for complete hydrogenation of alkynes. Lindlar's catalyst (Pd on CaCO3 with Pb(OCOCH3)2 and quinoline) is used to stop the process at a cis alkene stage.
- With Lindlar's catalyst, one equivalent of H₂ adds to an alkyne to form the cis product. The cis alkene product is unreactive to further reduction.
Oxidation and Reduction - Alkyne reduction to a Trans Alkene
- Dissolving metal reduction (Na in NH3) is a stereoselective reaction that yields the trans alkene product.
- The trans alkene is preferred because the vinyl carbanion formed is more stable with larger R groups further apart, avoiding steric interactions
Oxidation and Reduction - Summary of Alkyne Reductions
- Summary of three methods for reducing alkynes to alkanes or cis and trans alkenes. Includes relevant reagents (H₂, Pd-C, Lindlar's catalyst, Na in NH3)
Oxidation and Reduction - Reduction of Polar C-X Bonds
- Alkyl halides and epoxides can be reduced to alkanes and alcohols using LiAlH4.
- This reaction follows an SN2 mechanism.
- Unhindered, primary alkyl halides are reduced more easily than secondary or tertiary halides.
- In unsymmetrical epoxides, nucleophilic attack occurs at the less substituted carbon atom.
Oxidation and Reduction - Oxidizing Agents
- Two main categories of oxidizing agents:
- Reagents with an oxygen-oxygen bond (O2, O3, H2O2, peroxyacids)
- Reagents with metal-oxygen bonds (CrO3, Na2Cr2O7, K2Cr2O7, KMnO4, OsO4, Ag2O).
- Peroxyacids have the general formula RCO3H.
Oxidation and Reduction - Epoxidation
Epoxidation adds a single oxygen atom to an alkene, typically using a peroxyacid, to form an epoxide
- Epoxidation proceeds via syn addition of O to the alkene double bond.
- Cis alkenes yield a cis epoxide while trans alkenes yield trans epoxides.
Oxidation and Reduction - Dihydroxylation
- Dihydroxylation adds two hydroxyl (OH) groups to a double bond, producing a 1,2-diol (glycol).
- Depending on the reagent used, the addition can occur on the same side (syn) or opposite sides (anti) of the double bond.
- Anti-dihydroxylations commonly proceed with an epoxide intermediate.
- Syn dihydroxylation is typically performed using KMnO4 or OsO4.
- The Baeyer test for unsaturation uses dilute KMnO4.
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Description
This quiz focuses on the concepts of oxidation and reduction as covered in Chapter 1, Part B of the Advanced Organic Chemistry course for MSC students. It explores various methods and agents involved in these reactions, aiding in understanding key processes in organic chemistry. Perfect for those studying under Dr. Dima Sabbah during Fall 2014.
