Vibrations of Free Molecules - 3. Forms of Vibration of Aromatic Rings in Melamin
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| License | CC Attribution - NonCommercial - NoDerivatives 3.0 Germany: You are free to use, copy, distribute and transmit the work or content in unchanged form for any legal and non-commercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.3203/IWF/C-1211eng (DOI) | |
| IWF Signature | C 1211 | |
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| Production Year | 1975 |
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| IWF Technical Data | Film, 16 mm, LT, 43 m ; F, 4 min |
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00:00
MoleculeCycloalkaneDeformation (mechanics)MoleculeStarvation responseAromaticityMelamineThermoforming
00:52
Infrarot-SpektrumCycloalkaneDeformation (mechanics)GasverflüssigungNitrosamineMolecular geometryAtomic numberSunscreenDipol <1,3->MoleculeRaman scatteringDeformityStickstoffatomHyperpolarisierungMelaminePhase (waves)Deformation (mechanics)IonenbindungFunctional group
Transcript: English(auto-generated)
00:03
Vibrations of free molecules. Vibration modes of aromatic rings, as in melamine. We will now look at some typical vibrations of a relatively large organic molecule, melamine.
00:29
We shall only consider three skeletal or ring vibrations. The in-phase stretching vibration of the ring, or ring breathing. The in-plane ring deformation, and the out-of-plane ring deformation.
00:47
Here we see the melamine molecule drawn in perspective. All the atoms lie in a plane. Both infrared and Raman spectra contain a large number of bands.
01:10
One of the strongest Raman bands is due to the ring breathing vibration.
01:24
As you can see, all bands stretch and contract in phase. The molecule breathes. The vibrational amplitudes are now magnified by a factor of 10. The in-plane ring deformation also leads to a strong Raman band.
02:11
You can see not only the large variations in the bond angles in the ring, but also variations in the length of the CN bonds. The NH2 groups move only slightly.
02:41
The out-of-plane ring deformation shows a strong infrared band. All six nitrogen atoms vibrate in one direction. That is, out of the plane of the molecule.
03:06
All the remaining atoms move in the opposite direction. This leads to the generation of a dipole moment perpendicular to the plane of the molecule. The polarity of this dipole moment changes with the frequency of the vibration,
03:24
causing the infrared band to be very strong.