SPECTROSCOPY REVISION PLACE MAT- https://www.tes.com/teaching-resource/vce-spectroscopy-revision-poster-ir-nmr-and-ms-12042499
Spectroscopy techniques
In spectroscopic techniques, the atom or molecule absorbs a certain quantum of energy which causes the atom or molecule to move to a higher energy level.
Atoms- movement of electrons to higher level. Molecules- movement of electrons to higher level, movement of molecules to a higher vibrational, rotational and nuclear spin energy levels. The energy difference in each case is given by ∆E = hv, where v is the frequency and h is the Planck constant- 6.63x10^-34 Js |
|
Types of Energy
Electronic- Movement of electrons to other orbitals
Vibrational-Movement within molecules- towards or away from other atoms within the molecule. Rotational-Rotation (turning) of molecules. Translational-Movement of entire molecules in different directions. Infra Red SpectroscopyThe energy from Infrared radiation is not enough to promote an electron into a higher energy level but it is enough to cause changes to the bonds in molecules. •Just as electrons can occupy discrete energy levels, molecules occupy discrete vibrational energy levels. As the molecule moves to a higher vibrational energy level the frequency of the stretching vibration increases , •All molecules absorb infrared radiation and will absorb different levels of radiation depending on which bonds have been distorted. Infra Red spectroscopy can stretch, bend (scissor), wag and twist the bonds of molecules. Stretching animation by By No machine-readable author provided. Tiago Becerra Paolini assumed (based on copyright claims). [Public domain], via Wikimedia Commons
|
Rotational and vibrational energy By en:User:Greg L [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
Bending or scissoring animation By No machine-readable author provided. Tiago Becerra Paolini assumed (based on copyright claims). [Public domain], via Wikimedia Commons
Twisting animation By mailto:[email protected] (Own work) [CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons
|
Energy absorbed
•The range of energies absorbed depends on the strength of the bonds.
•The mass of the atoms attached to the bond also affects the energy absorbed
•Infrared absorption is measured in wavenumbers (cm-1).
•Wavenumbers are the reciprocal of wavelengths – 1/λ.
•The mass of the atoms attached to the bond also affects the energy absorbed
•Infrared absorption is measured in wavenumbers (cm-1).
•Wavenumbers are the reciprocal of wavelengths – 1/λ.
IR values from the VCE data booklet- see link.
|
The spectrum produced will show us areas of absorption particular bonds and functional groups.
•The spectrum will also give us an idea of other bonds present in the molecule that will determine the structure. No two molecular compounds are identical in bonds and bonding environment and so infrared spectroscopy can give us a characteristic fingerprint for each compound. •The infrared spectrum above 1000cm-1 is used to identify functional groups. •The spectrum at frequencies less than 1000cm-1 is characteristic of a particular compound. This region is largely a result of bending and stretching of the entire molecule and so is unique to a particular compound. Three very important regions to know are: (see the table above for values) O-H stretch C-H stretch C=O stretch |
IR diagram See page for author [Public domain], via Wikimedia Commons
|
Image from Wikimedia commons
|
|