Vibrations of Free Molecules - 3. Forms of Vibration of Aromatic Rings in Melamin

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Vibrations of Free Molecules - 3. Forms of Vibration of Aromatic Rings in Melamin
Alternative Title
Schwingungen freier Moleküle - 3. Schwingungsformen aromatischer Ringe in Melamin
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C 1211
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Film, 16 mm, LT, 43 m ; F, 4 min

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The movement of the atoms during the more important normal vibrations of melamine are shown in perspective representation: stretching and bending vibrations of the aromatic ring in the melamine molecule. The in-phase and out-of-phase movements as well as the concept of characteristic vibrations become clear in the process.
Keywords molecular structure oscillations / in molecules
Molecule Melamine Molecule Cycloalkane Deformity Deformation (mechanics) Thermoforming Aromaticity
Molecule Raman scattering Deformation (mechanics) Phase (waves) Infrarot-Spektrum Melamine Sunscreen Cycloalkane Atomic number
Raman scattering Infrarot-Spektrum Molecular geometry Cycloalkane Deformity Deformation (mechanics)
Molecule Stickstoffatom Cycloalkane Deformity Dipol <1,3-> Atomic number
Molecule Hyperpolarisierung Dipol <1,3->
Gasverflüssigung Nitrosamine
Vibrations of Free Molecules - Forms of Vibration of Aromatic Rings as in Melamin We will now look at some typical vibrations of a relatively large organic molecule, melamine. 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. 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. One of the strongest Raman bands is due to the ring breathing vibration. 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. 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 NH 2-groups move
only slightly. 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. 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 causing the infrared band to be very strong.


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