Transcript CH 9-1 Power Point

Chapter 9: Spectroscopic
Identification of Organic Compounds
CH 9-1: Review of IR and Hydrogen Deficiency
•Infrared (IR) Spectroscopy: used to determine the
functional groups present in an organic compound.
•Nuclear Magnetic Resonance (NMR) Spectrometry: helps
to identify the C-H framework of an organic compound.
•Mass Spectrometry (MS): used to determine the molecular
mass of organic compounds, and to identify certain
structural features of the compound.
•Information from all three instrumental techniques is
usually required to help identify the structure of an
unknown organic compound.
Review (Chap 2): Infrared (IR) spectroscopy
•IR is an instrumental method
used to identify some of the
functional groups present in
an organic compound.
•Basic Theory: A molecule is
subjected to electromagnetic
radiation (EMR) at a frequency
in the IR region of the
electromagnetic spectrum.
•When the IR frequency
matches the vibrational
frequency of a specific
functional group, we observe
an energy absorbance band in
the IR spectrum.
Example IR spectrum of organic compound:
The absorption bands represent IR energy absorbed by the
covalent bonds of different functional groups, read as
frequency units off the x-axis (4000 - 600 cm-1).
Most of these bands are due to C-C and C-H bonds and can
be ignored.
The absorption bands of different functional groups absorb
at different frequencies and intensities. Keep it simple!
(~3300 if terminal)
Tool for Unknown Identification:
Hydrogen Deficiency
• Hydrogen Deficiency – measure of unsaturation, or
deficiency in the #H’s you would expect vs #C’s.
• A “deficiency” in the number of hydrogens indicates the
presence of pi bonds or rings.
HD = (Max # H’s – Actual # H’s)
(Max #H’s = 2n + 2
where n = #carbons)
HD for double bond = 2
HD for ring = 2 (cycloalkane)
HD for triple bond = 4
HD for benzene ring = 8
Combinations are possible!