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CHEM205: Spectroscopy

Unit 3: Infrared Spectroscopy   Infrared (IR) spectroscopy is a spectroscopic technique that deals with the infrared region of the electromagnetic spectrum.  The spectra arise from vibrational and rotational states of excited molecules.  IR spectroscopy can be used to identify compounds and investigate sample compositions.

This unit begins with discussion of the general principles and the instrumentation of IR spectroscopy.  It continues with information on vibrational and rotational modes of molecules, followed by an explanation of how Hooke’s Law, which is generally applied to springs in physics courses, can be used to describe the motions of molecular bonds.  The unit continues with details of spectral interpretation of organic molecules and concludes with a discussion of other applications.       

Unit 3 Time Advisory
This unit will take approximately 21 hours to complete.

☐    Subunit 3.1: 3.0 hours

☐    Subunit 3.2: 0.5 hours

☐    Subunit 3.3: 0.5 hours

☐    Subunit 3.4: 12.0 hours

☐    Reading: 6.0 hours

☐    Lecture: 1.0 hour

☐    Assignments: 5.0 hours

☐    Subunit 3.5: 3.0 hours

☐    Subunit 3.6: 2.0 hours

Unit3 Learning Outcomes
Upon successful completion of this unit, the student will be able to:

  • Identify the components of an infrared spectrophotometer.
  • Describe the vibrational and rotational modes of molecules and how they contribute to the IR spectra.
  • Understand the application of Hooke’s Law to stretching frequencies in molecular bonds.
  • Determine the absence or presence of functional groups within a molecule based on the location and shape of IR bands.
  • Use infrared spectra to determine the structure of organic molecules.
  • Discuss other applications of infrared spectroscopy.

3.1 Instrumentation   - Reading: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: Instrumentation” Link: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: Instrumentation” (HTML)
 
Instructions: Click on the “IR” button on the left-hand side of the webpage, then click on the link “Instrumentation” (Section II).  This material shows a schematic diagram of a typical IR spectrophotometer.
 
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  • Reading: William Reusch’s “Virtual Text of Organic Chemistry: Infrared Spectroscopy” Link: William Reusch’s “Virtual Text of Organic Chemistry: Infrared Spectroscopy” (HTML and Java)
     
    Instructions: Please read the entire webpage.  Please use the corresponding buttons in the second section, “Vibrational Spectroscopy,” to view the bending and stretching modes.  Also, be sure to follow the links in the third section, “Group Frequencies,” to view the subtle differences in spectra within different functional groups.  This supporting information is advantageous in the successful completion of this course.  This material covers all subunits in Unit 3. 
     
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  • Assessment: William Reusch’s “Virtual Text of Organic Chemistry: Spectroscopy Problems” Link: William Reusch’s “Virtual Text of Organic Chemistry: Spectroscopy Problems”(HTML)
     
    Instructions: Please work through each of the four problems, following the instructions given on the page to navigate the assessment.  This site is designed to require you to attempt the problems prior to obtaining the solutions from its answer key.  This material covers concepts from all of Unit 3. 
     
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3.2 Vibrational/Rotational Modes   - Reading: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: Molecular Vibrations” Link: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: Molecular Vibrations” (HTML)
 
Instructions: Click on the “IR” button on the left-hand side of the webpage, then click on the link “Molecular Vibrations” (Section I, B).  This material provides an explanation of vibrations and animations of stretching and bending modes that occur during IR spectroscopy measurements. 
 
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3.3 Hooke’s Law   - Reading: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: Infrared Spectroscopy Basics” Link: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: Infrared Spectroscopy Basics” (HTML)
 
Instructions: Click on the “IR” button on the left-hand side of the webpage, then click on the link “Infrared Spectroscopy Basics” (Section I, C).  This material discusses the application of Hooke’s law, which usually applies to force constants in springs, to the molecular vibrations in IR spectroscopy. 
 
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3.4 Interpretation of Infrared Spectra   - Reading: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: General Approach to IR Spectrum Analysis” Link: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: General Approach to IR Spectrum Analysis” (HTML)
 
Instructions: Click on the “IR” button on the left-hand side of the webpage, then click on the link “General Approach to IR Spectrum Analysis” (Section III).  This material gives a step-by-step approach to obtaining structural data from an IR spectrum.
 
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  • Reading: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: Example Spectra for Various Functional Groups” Link: Central Connecticut State University: Dr. Neil Glagovich’s “Infrared Spectroscopy: Example Spectra for Various Functional Groups” (HTML)
     
    Instructions: Click on the “IR” button on the left-hand side of the webpage, then follow the links (A–Y) below “Section V: Example Spectra for Various Functional Groups.”  This material provides representative spectra for each organic functional group.  Section IV presents a table of the key wavenumber assignments in the spectra.
     
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  • Lecture: OCHeM.com: Thomas Poon’s “Infrared Spectroscopy” Link: OCHem.com: Thomas Poon’s “Infrared Spectroscopy” (QuickTime)
     
    Instructions: Scroll down the list of “PreLectures” to find a link entitled “Infrared Spectroscopy.”  Click on the link; it will launch a QuickTime application in a new window.  Watch the video (runtime = 25:28 minutes), which explains the presentation of IR peaks and details structure elucidation from a given IR spectrum.
     
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  • Lecture: OCHeM.com: Thomas Poon’s “Spectroscopy, Part 2 of 4” Link: OCHem.com: Thomas Poon’s “Spectroscopy, Part 2 of 4” (QuickTime)
     
    Instructions: Scroll down the list of “PreLectures” to find a link entitled “Spectroscopy, Part 2 of 4.”  Click on the link; it will launch a QuickTime application in a new window.  Watch the video (runtime = 13:24 minutes), which demonstrates the use of both IR and MS for organic structure determination.
     
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  • Assessment: OCHeM.com: Thomas Poon’s “IR Spectroscopy Problems” Link: OCHeM.com: Thomas Poon’s “IR Spectroscopy Problems” (HTML or PDF)
     
    Instructions: Please work through these problems dealing with infrared spectroscopy.  Then, click here for the answer key.
     
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  • Assessment: OCHeM.com: Thomas Poon’s “IR and Mass Spec Problems” Link: OCHeM.com: Thomas Poon’s “IR and Mass Spec Problems” (HTML or PDF)
     
    Instructions: Please work through these problems dealing with structure identification from infrared spectra combined with mass spectra.  Then, click here for the answer key.
     
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3.5 Organic Functional Group Frequencies   - Reading: Connexions: Andrew R. Barron’s “Characteristic IR Vibrational Modes for Hydrocarbon Compounds” Link: Connexions: Andrew R. Barron’s “Characteristic IR Vibrational Modes for Hydrocarbon Compounds” (HTML or PDF)
 
Instructions: This material can also be viewed in PDF form by clicking “Download” in the top right corner of the page. This material presents the general vibrational mode frequencies for functional groups in tabular form.  Please remember the shape of the bands also reveals much of the structural information.       
 
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  • Interactive Lab: Jean-Claude Bradley and Andrew Lang’s “Spectral Game” Link: Jean-Claude Bradley and Andrew Lang’s “Spectral Game” (HTML)
     
    Instructions: Please enter a username in the required field.  Note: You do not need to register and this does not need to be your actual name (i.e., student1).  Choose the format you prefer for your viewer and select IR from the “Type” drop-down box.  A general video tutorial from the creators of the game can be found here.  Please spend an ample amount of time using this game as a learning tool to increase your spectral analysis proficiency.
     
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3.6 Other Applications of Infrared Spectroscopy   3.6.1 Metal-Ligand Complexes   - Reading: Connexions: Jiebo Li and Andrew R. Barron’s “Fourier Transform Infrared Spectroscopy of Metal Ligand Complexes” Link: Connexions: Jiebo Li and Andrew R. Barron’s “Fourier Transform Infrared Spectroscopy of Metal Ligand Complexes” (HTML or PDF)
 
Instructions:  Please read the entire webpage. You can also see this material in PDF form by clicking “Download” on the top right corner of the page. This material reviews the basics of infrared spectroscopy and describes some key shift and intensity differences observed in the spectra of metal ligand complexes.
 
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3.6.2 Functional Group Vibrational Lifetimes   - Reading: Connexions: Xiewen Wen and Andrew R. Barron’s “Pump-Probe Detection of Molecular Functional Group Vibrational Lifetime” Link: Connexions: Xiewen Wen and Andrew R. Barron’s “Pump-Probe Detection of Molecular Functional Group Vibrational Lifetime” (HTML or PDF)
 
Instructions: Please read the entire webpage.  You can also see this material in PDF form by clicking “Download” on the top right corner of the page.  This material describes a technique used to measure the lifetimes of vibrational excited states.
 
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