INFRARED SPECTROSCOPY

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INFRARED SPECTROSCOPY
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RHS UnitThe Buck Infrared Spectrophotometer
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THE ELECTROMAGNETIC SPECTRUM
Frequency (n)
low
high
high
low
Energy
MICRO- WAVE
X-RAY
ULTRAVIOLET
INFRARED
RADIO
FREQUENCY
Nuclear magnetic resonance
Vibrational infrared
Ultraviolet
Visible
2.5 mm
15 mm
1 m
5 m
200 nm
400 nm
800 nm
BLUE
RED
Wavelength (l)
short
long
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Types of Energy Transitions in Each Region
of the Electromagnetic Spectrum
REGION
ENERGY TRANSITIONS
X-ray
Bond-breaking
UV/Visible
Electronic
Infrared
Vibrational
Microwave
Rotational
Radio Frequency
Nuclear and
(NMR)
Electronic Spin
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Simplified Infrared Spectrophotometer
NaCl plates
focusing mirror
Detection Electronics and Computer
Determines Frequencies of Infrared Absorbed
and plots them on a chart
Infrared Source
Sample
intensity of absorption
Absorption peaks
frequency
(decreasing)
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4-Methyl-2-pentanoneC-H lt 3000, CO _at_ 1715 cm-1
KETONE
fingerprint
diagnostic
AN INFRARED SPECTRUM
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Propanenitrile
NITRILE
BASE 2250

CN
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1-Hexyne
ALKYNE
BASE 2150

C-H

CC
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THE UNIT USED ON AN IR SPECTRUM IS
WAVENUMBERS ( n )
n wavenumbers (cm-1)
1
n
l wavelength (cm)

l
(cm)
c speed of light
n frequency nc
c 3 x 1010 cm/sec
or
( )
1
cm/sec
1
c
n
c


l
l
cm
sec
wavenumbers are directly proportional to frequency
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Molecular vibrations
Two major types
STRETCHING
C C
C
BENDING
C
C
both of these types are infrared active
( excited by infrared radiation )
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Typical Infrared Absorption Regions
(stretching vibrations)
WAVELENGTH (mm)
C-Cl
CO
CN
O-H
C-H
C N
Very few bands
C-O
CC
N-H
C C
C-N
XCY
C-C

NO NO
(C,O,N,S)
FREQUENCY (cm-1)
nitro has two bands