IR Spectroscopy Flashcards
What are the use of analytical spectroscopy in pharmaceutical analysis
> Infrared spectrometry - qualitative and quantitative analysis
NMR spectrometry - qualitative and quantitative analysis
Atomic spectroscopy - qualitative and quantitative analysis
What are the different types of energies
> High energy radiation (X-rays) can break bonds.
Medium energy light (UV/Vis) can cause electrons to be excited from one orbital to the next.
Lower energy light (IR) can cause bonds to vibrate (stretch and bend)
Even lower energy light can just cause atoms to change the direction they are rotating in.
What is the quantum theory on about molecules
molecules or atoms will only absorb the energy they need to undergo the specific change
What is the beer-lambert law
A=ecl
ABSORPTION of light = Molar absorptivity * conc * pathlength
there is a linear relationship between the concentration and the absorbance of the solution
What is infrared spectroscopy
Nuclei of atoms covalently bonded naturally vibrate - occur at “Quantised Energy Levels”
When molecules are exposed to light with energy corresponding to the quantised amount needed to go from one vibrational state to the next, this wavelength (l) will be absorbed, leading to an “Excited Vibrational State”.
Qualitative analysis of infrared spectroscopy
The higher the wave number the higher energy absorbed by the bond.
The stronger the bond and the heavier the atoms attached the more energy is needed to vibrate the bond
strengths of IR technique in pharmaceutical analysis
> Quick and relatively cheap spectroscopic technique
Useful if you are looking to identify certain functional groups in molecules
The IR Fingerprint region of a compound is unique and therefore serves as a fingerprint for this compound.
Providing you have a sharp peak well away from other peaks that is only due to an analyte of interest the Beer-Lambert law applies (A=ecl) so IR can be used quantitatively.
Limitations of the IR spec
> Unusual to be able to use IR alone for structure determination
> Rarely used for quantitative analysis as difficult to find a absorption peak well separated from other peaks.
> Intermolecular bonding (e.g. hydrogen bonding in OH groups) can effect the strength of the bonds so alter the energy needed to vibrate it.
-This can lead to broad peaks and makes the Beer-Lambert law invalid as it only works for single state systems.
What pharmaceutical applications of IR spec
Used to check the progress of a reaction
- Identification of the fingerprint region and computer searchable libraries
- Can be quantitative
What do some of the data peaks in the IR spec
OH: Stretch - 3100-3600
CH stretch: <3000 - Few sharp peaks
CH bend: <1450-1375 - Sharp
C=O: 1710 - sharp
