Infrared Flashcards
What happens to the molecule when it absorbs IR radiation?
The molecule will absorb the radiation that matches the frequency of the vibration of one of its bonds,
What needs to be happening inside the molecule in order to see a peak?
Needs to be a change in dipole moment for detection of wavelength
(No change in dipole movement - no detection of signal)
Why do different functional groups have peaks at different wave numbers?
Absorbance of specific wavelengths results in specific movements
(Bonds and stretched can be correlate to functional group)
Absorbances - functional group info.
How do wave numbers and energy relate?
Wave numbers and energy are proportional
Why do OH binds give wide peaks in high concentration solutions?
Why are the peaks narrow when at low concentration?
Hydrogen bonding can result in shifts in the location and changes the shape of the peak depending on the bonds.
Extra bonds need extra energies which are in different parts of the spectra
Why do we use salt plates? What are the used for?
We use salt plates because they do not absorb IR radiation
(Used to hold and analyze a solution in IR radiation)
Name and describe the techniques used to analyze solids using an IR instrument that does not have an ATR
Nujol Mull - mineral oil
(Mortar & pestle - 5-10g analyte - few drops nujol - salt plate - analyze)
Smear - solvent
(Dissolve - 5-10g analyte - solvent eg dichloromethane - salt plate - evaporate - analyze)
KBr - KBr
(KBr + solid sample - die set - squeeze out sample - analyze)
What changes about the spectra when we want to quantitate using IR?
Changes from % transmission to absorbance
What situation makes quantitation possible?
Absorbance is directly proportional to concentration.
What does FT stand for?
Fourier Transform
What unique feature/component does an FTIR have? What does this component product?
Interferometer
Products a interferogram (needs FT to completely the gram)
Why do we take the background?
To reduce the impact of air
Name a commonly used source of IR radiation
Silica carbide rod with electrical current
Why can we not use the same detectors used in UV/Vis for IR?
Infrared photons are not as energetic as UV/Vis photons
(Cannot detect by ejecting electrons or promoting them)
What is one type of detector that is used for IR?
Thermocouple
(Blackened to absorb radiation, so it’s temp becomes sensitive to radiation)
