M4 Chapter 17 - Analytical Techniques Flashcards
(18 cards)
What happens when a molecule absorbs infrared radiation?
It makes the covalent bond vibrate more in a stretching or bending motion
What factors affect the amount of vibration of a bond?
Bond Strength
Bond Length
Mass of each atom in the bond
How does infrared spectroscopy work?
Every bond has a unique vibration frequency in the infrared region of the EM spectrum
Bonds absorb radiation that has the same frequency as their frequency of vibration.
Infrared radiation emerged from sample is missing the frequencies that have been absorbed. Hence this information can be used to work out the compound’s functional group.
What do the peaks on an infrared spectrum represent?
Absorbance of energy from the infrared radiation.
What are the 2 peaks that must be present to identify a substance as Carboxylic Acid?
Broad peak at 2500 - 3300cm-1.
Sharp peak at 1680 - 1750cm-1.
What happens inside a mass spectrometer?
Organic compound is vaporised and passed through the spectrometer.
Some molecules lose an electron and form molecular ions.
Excess energy from the ionisation makes the bonds vibrate more.
Vibration makes the bond weaken.
Molecular ion splits by fragmentation.
What is the symbol of molecular ion?
M+
Is fragmentation predictable? Why?
No because it can occur anywhere in the molecule.
In a mass spectrometry how is a molecular ion represented?
It is the peak with the highest mass/charge ratio.
The molecular mass of the molecular ion is equal to what?
Mr
Will the molecular ion peaks of two isomers of the same compound be the same or different?
Same
What is the m/z value of CH3+?
15
What is the m/z value of OH- from alcohol?
17
What is the m/z value of C2H5+?
29
What is the m/z value of C3H7+?
43
What is the m/z value of C4H9+?
57
What are the advantages of mass spectrometry? (2)
Cheap
Small quantities of sample are required
What is the main disadvantage of using mass spectrometry?
The sample is completely destroyed.
