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Unformatted text preview: B.
C. 8.5 m
9.7 m 25 Question 2
H • The molecule formaldehyde
H has six vibrational
has six vibrational • The hydrogen atoms have an asymmetrical and a
symmetrical stretch with the following frequencies:
8.55 x 1013 s-1, 8.36 x 1013 s-1.
• What wavelength corresponds to these vibrations?
• Find the energy in J of each vibration. Which
vibrational mode uses the most energy?
26 13 Using IR spectroscopy to Identify
• Because IR frequencies provide information
about bonds between atoms, it is very useful
for identifying functional groups:
Functional Group Characteristic Vibration wavelength -OH
CN O-H stretch
C N stretch 2.7
4.4 The IR stretching frequency is often highly
characteristic for a given functional group m
27 Three C4 Compounds
C2H5OC2H5 C4H9OH C2H5NHC2H5
Energy increases 28 14 Summary
• Light interacts with matter
– Bonds break, vibration, rotation • Uneven distribution of charge in molecule or
distribution of charge in molecule or
upon vibration allows for absorption of IR light
– CO2, N2O, H2O, and chlorofluorocarbons (CFCs)
are Greenhouse gases
– Identification of functional groups
– Absorption frequencies depend on mass of atoms
bonded and bond strength 29 15...
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- Fall '02