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CHEM201: Advanced Organic Chemistry

Unit 1: Reactive Reaction Intermediates   A reaction intermediate is a short-lived compound that is generated in a chemical reaction.  These intermediates are very important because their isolation, though difficult, can provide very important insight into the mechanism of the reaction.  When the intermediate cannot be isolated, evidence of its existence can be seen through spectroscopic methods. 
           
In this unit,we study the chemistry behind some of the important reaction intermediates. We will first discuss ylides, their preparation, and reactions.  We will then study benzynes, and finally we will discuss free radicals.

Unit 1 Time Advisory
This unit should take you approximately 17 hours to complete.

☐    Subunit 1.1: 5 hours

☐    Subunit 1.1.1: 2 hours

☐    Subunit 1.1.2: 1.5 hours

☐    Subunit 1.1.3: 1.5 hours

☐    Subunit 1.2: 4 hours

☐    Subunit 1.2.1: 2 hours

☐    Subunit 1.2.2: 2 hours

☐    Subunit 1.2.2.1: 1 hour

☐    Subunit 1.2.2.2: 1 hour

☐    Subunit 1.3: 8 hours

☐    Subunit 1.3.1: 3 hours

☐    Subunit 1.3.2: 2 hours

☐    Subunit 1.3.2.1: 1 hour

☐    Subunit 1.3.2.2:1 hour

☐    Subunit 1.3.3: 3 hours

Unit1 Learning Outcomes
Upon successful completion of this unit, the student will be able to:

  • Identify phosphorus, sulfur, and nitrogen ylides.
  • Formulate a mechanism for the Wittig reaction.
  • Enumerate the reactions to prepare benzynes.
  • List the reactions of benzynes.
  • Formulate the mechanism for the reaction of benzynes.
  • Define free radical.
  • Formulate reactions to prepare free radicals.
  • List reactions of free radicals.

1.1 Ylides   - Reading: Metropolitan State College of Denver: Professor Milton Weider’s “Advanced Organic Chemistry: Ylides” Link: Metropolitan State College of Denver: Professor Milton Weider’s “Advanced Organic Chemistry: Ylides” (PowerPoint)
 
Instructions: Click on the file named “Ylides.ppt” to view the file titled “Ylides.”  This presentation will provide a general overview of ylides and how to prepare them (Section 1.1.1). In this presentation, reaction of ylides will also be discussed. This section also provides method and preparation of nitrogen and sulfur ylides (Sections 1.1.2 and 1.1.3).
 
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1.1.1 Preparation of Ylides and Wittig Reaction   Note: This subunit is covered by the reading assigned beneath subunit 1.1.  Focus specifically on slides 1–5 as they focus on the preparation of ylides and the Wittig reaction.

1.1.2 Sulfur Ylides   Note: This subunit is covered by the reading assigned beneath subunit 1.1.  Focus specifically on slides 7–8 as they focus on the preparation of sulfur ylides.

1.1.3 Nitrogen Ylides   Note: This subunit is covered by the reading assigned beneath subunit 1.1.  Focus specifically on slide 6 as it focuses on the preparation and reactions of nitrogen ylides.

  • Assessment: The Saylor Foundation’s “Chemistry of Ylides” Link: The Saylor Foundation’s “Chemistry of Ylides” (PDF)
     
    Instructions: Please complete the assessment.  You can check your answers with the answer key provided here. (PDF)

1.2 Benzynes   - Reading: University of Calgary: Professor Ian Hunt’s “Organic Chemistry: Benzyne” Link: University of Calgary: Professor Ian Hunt’s “Organic Chemistry: Benzyne” (HTML)
 
Instructions: Please read the section titled “Benzyne” to gain a general understanding of benzyne.  This section provides an explanation of the geometry of benzyne, which is the main reason for its high reactivity.
 
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1.2.1 Preparation of Benzynes   - Reading: Metropolitan State College of Denver: Professor Milton Weider’s “Advanced Organic Chemistry: Benzynes” Link: Metropolitan State College of Denver: Professor Milton Weider’s “Advanced Organic Chemistry: Benzynes” (PowerPoint)
 
Instructions: Click on the file named “Benzynes.ppt” to view the file titled “Benzynes.”  This presentation will provide a general overview of benzynes and how to prepare them. In this presentation, reaction of benzynes will also be briefly discussed.  For a more detailed presentation of the reactions of benzynes, please refer to the links in section 1.2.2.

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1.2.2 Reactions of Benzynes   1.2.2.1 Nucleophilic Reactions   - Reading: University of Calgary: Professor Ian Hunt’s “Organic Chemistry: Addition Reactions of Benzyne” Link: University of Calgary: Professor Ian Hunt’s “Organic Chemistry: Addition Reactions of Benzyne” (HTML)
 
Instructions: Please read the section titled “Addition Reactions of Benzyne” to gain a general understanding of the mechanism behind addition reactions of benzyne.
 
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1.2.2.2 Cycloadditions   - Reading: University of Calgary: Professor Ian Hunt’s “Organic Chemistry: Diels-Alder Reactions of Benzyne” Link: University of Calgary: Professor Ian Hunt’s “Organic Chemistry: Diels-Alder Reactions of Benzyne” (HTML)
 
Instructions: Please read the section titled “Diels-Alder Reactions of Benzyne” to gain a general understanding of the mechanism behind this very important cycloaddition reactions of benzyne.  Cycloaddition reaction is a peryclic reaction in which two or more unsaturated molecules combine to form a cyclic product.
 
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  • Assessment: The Saylor Foundation’s “Reactions of Benzynes” Link: The Saylor Foundation’s “Reactions of Benzynes” (PDF)
     
    Instructions: Please complete the assessment.  You can check your answers with the answer key provided here. (PDF)

1.3 Free Radicals   A radical is an unpaired electron that arises from homolytical cleavage of a chemical bond.  Free radicals are extremely important for many reactions and life processes, such as the function of our immune systems.  When your body is attacked by foreign invaders, your immune system recognizes this through free radicals, and therefore, it is able to defend against the attack.  The introduction to this course mentions how white blood cells, which overproduce oxygen-based free radicals, defend against infection.
 
Note: Free radicals are an example of homolytic bond cleavage, as you learned in your previous organic chemistry course.  Here, we go into more detail about radicals, their bond dissociation energies, and the mechanisms of radicals.   

  • Reading: Michigan State University: Professor William Reusch’s “Virtual Textbook of Organic Chemistry: Free Radicals: Organic Radicals” Link: Michigan State University: Professor William Reusch’s “Virtual Textbook of Organic Chemistry: Free Radicals: Organic Radicals” (HTML)
     
    Instructions: Please read the section titled “Free Radicals” to gain a general understanding of what free radicals are.  This section also provides a detailed explanation of reactions of free radicals and their stability (Sections 1.3.1 and 1.3.3).
     
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1.3.1 Stability of Radicals   - Reading: University of Texas at Austin: Professor Nathan Bauld’s “Mechanisms and Theory of Organic Reactions: Free Radicals: Radicals and Radical Reactions” Link: University of Texas at Austin: Professor Nathan Bauld’s “Mechanisms and Theory of Organic Reactions: Free Radicals: Radicals and Radical Reactions” (HTML)
 
Instructions: Please read the section titled “Radicals and Radical Reactions” to gain a general understanding of the stability of free radicals.  
 
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1.3.2 Free Radical Initiators   - Reading: Metropolitan State College of Denver: Professor Milton Weider’s “Advanced Organic Chemistry: Free Radical Initiators” Link: Metropolitan State College of Denver: Professor Milton Weider’s “Advanced Organic Chemistry: Free Radical Initiators” (PowerPoint)
 
Instructions: Click on the file named “Radicals.ppt” to view the file titled “Free Radicals.”  This presentation will provide a general overview of methods of preparation of radicals.
 
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1.3.2.1 Oxygen Containing Compounds   Note: This subunit is covered by the reading assigned beneath subunit 1.3.2.  Focus specifically on slide 9 as it focuses on the initiation of oxygen containing compounds.

1.3.2.2 Decomposition of Azo Compounds   Note: This subunit is covered by the reading assigned beneath subunit 1.3.2.  Focus specifically on slide 10 as it focuses on the decomposition of nitrogen containing compounds.

1.3.3 Reactions of Radicals   Note: The reaction section of this unit covers all of the common reactions, such as oxidation, addition, rearrangements, and substitution reactions commonly found to involve radicals. This subunit is covered by the reading assigned beneath subunit 1.3.  Please scroll down to the section titled “Reactions of Free Radicals” to gain a general understanding of the reactions of free radicals. 

  • Assessment: The Saylor Foundation’s “Reactions of Free-Radicals” Link: The Saylor Foundation’s “Reactions of Free-Radicals” (PDF)
     
    Instructions: Please complete the entire assessment.  You can check your answers against the Answer Key (PDF).