Infrared Spectroscopy
Jan 01, 2016
Infrared Spectroscopy
SpectroscopyThe energy of the interaction of
electromagnetic radiaiton (light) with moleculesSeveral different techniques:
Infrared spectroscopy Proton nuclear magnetic resonance Carbon-13 nuclear magnetic resonance
Infrared SpectroscopyProvides a simple and rapid instrumental
technique that can give evidence for the presence of various functional groups. Depends on the interaction of molecules and
atoms with electromagnetic radiationInfrared radiation causes atoms and groups of
atoms of organic compounds to vibrate with increases amplitude about the covalent bonds that connect them.
Infrared Spectrometer
Fourier Transform Infrared SpectrometerSplit radiation beam from the IR source so that it reflects simultaneously from a moving mirror and a fixed mirror, leading to interferencePass through the sample to the dectector and recorded as interferogram
http://www.wooster.edu/chemistry/analytical/ftir/default.html
Electromagnetic Radiation Radiation energy – has
wavelike properties Frequency (ν, Greek nu) – the
number of peaks (maxima) that pass by a fixed point per unit time (s-1 or Hz)
Wavelength (λ, Greek lambda) – the length from one wave maximum to the next
Amplitude – the height measured from the middle point between peak and trough (maximum and minimum)
Intensity of radiant energy is proportional to amplitude
Planck Equation Planck – energy radiated by a heated
object is quantized Radiant energy emitted in discrete units or
quanta The smallest quantity of energy that can be emitted in
the form of electromagnetic radiation
E = hν or h = 6.626 x 10-34 J•s (Planck’s constant) unit of E is J/proton
high energy radiation – higher ν, shorter λ low energy radiation – lower ν, higher λ
Vibration of moleculesTwo atoms are joined by a covalent bond that
can undergo a stretchingTwo factors contributed to stretching
Mass of bonded atomsRelative stiffness of the bond
http://upload.wikimedia.org/wikipedia/commons/6/60/Scissoring.gif
Vibration of molecules
Vibrations of atomsStretch: the distance between bonded atoms
oscillatesBend: bond angles oscillate
H
CH H
CH
Stretch bend
Characteristic Infrared Absorptions of Groups
Group Bond Frequency (cm-1)
Alkyl C-H 2853 - 2962
Alcoohol O-H 3590 - 3650
Amine N-H 3300 - 3500
Bond Frequency range (cm-1)
2100 -2260
2220 - 2260
1620 – 1680
1630 - 1780
C C
C N
C C
C O
A complete characteristics are given in table 2.7 page 79