CHY242
Organic Chemistry
II
Chapter 15
Infrared Spectroscopy
& Mass Spectrometry
Amir Kiumarsi
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15.1 Introduction to Spectroscopy
15.2 IR Spectroscopy
15.3 Signal Characteristics: Wavenumber
15.4 Signal Characteristics: Intensity
15.5 Signal Characteristics: Shape
15.6 Analyzing an IR Spectrum
15.7 Using IR to Distinguish between Two Compounds
15.8 Introduction to Mass Spectrometry
15.9 Analyzing the (M)+• Peak
15.10 Analyzing the (M+1) +• Peak
15.11 Analyzing the (M+2) +• Peak
15.12 Analyzing the Fragments
Chapter 10/2
15.14 Gas Chromatography—Mass
Spectrometry
15.1 Introduction to Spectroscopy
• Wavelength
• Frequency
Chapter 13/3
15.1 Introduction to Spectroscopy
• There are many wavelengths of light that cannot be observed with your eyes.
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.1 Introduction to Spectroscopy
• When light interacts with molecules, the effect depends on the wavelength of light used.
• This chapter focuses on IR spectroscopy.
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
Interaction Electromagnetic Radiation with Molecules
Chapter 13/6
Electromagnetic Spectrum
Absorption Spectra
Chapter 13/7
Electromagnetic Spectrum
• Absorption Spectra
Chapter 13/8
Interaction Electromagnetic Radiation with Molecules
p. 503
Infrared Spectroscopy
Wavenumber is the reciprocal of wavelength
Fig. 13-3, p. 505
Vibration in Organic Molecules
Vibration of Water (H2O):
•http://www.youtube.com/watch?v=1uE2lvVkKW0
•Vibrations of Molecules:
•http://www.youtube.com/watch?v=3RqEIr8NtMI
15.2 IR Spectroscopy
• Molecular bonds can vibrate by stretching or by bending in a number of ways.
• This chapter will focus mostly on stretching frequencies.
• Some night vision goggles can detect IR light that is emitted. Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.2 IR Spectroscopy
• The energy necessary to cause vibration depends on the type of bond.
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Klein, Organic Chemistry 1e
15.2 IR Spectroscopy
In the IR spectrum:
•% transmittance
•Wavenumber
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.2 IR Spectroscopy
IR spectrum characteristics
•WAVENUMBER
•INTENSITY
Strong, Moderate, weak
•SHAPE
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.3 IR Signal Wavenumber
• The WAVENUMBER for a stretching vibration depends on the bond strength and the mass of the atoms: bonded together
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.3 IR Signal Wavenumber
• Rationalize the trends below using the wavenumber formula: 1.
2.
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Klein, Organic Chemistry 1e
15.3 IR Signal Wavenumber
• The wavenumber formula and empirical observations allow us to designate regions as representing specific types of bonds.
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.3 IR Signal Wavenumber
• region above 1500 cm-1 is called the diagnostic region.
• The region below 1500 cm-1 is called the fingerprint region.
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.3 IR Signal Wavenumber
• Analyze the diagnostic and fingerprint regions below.
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.3 IR Signal Wavenumber
• Analyze the diagnostic and fingerprint regions below.
Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.3 IR Signal Wavenumber
• Compare the IR spectra. Copyright 2012 John Wiley & Sons, Inc.
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Klein, Organic Chemistry 1e
15.3 IR Signal Wavenumber
• Compare the IR stretching wavenumbers below.
• Are the differences due to mass or bond strength?
• Which bond is strongest, and WHY?
Copyright 2012 John Wiley & Sons, Inc.
