C17 Spectroscopy Flashcards
What happens when a molecule absorbs infrared radiation
It makes the CB 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 a sample is missing the frequencies that have been absorbed → this information can be used to identify 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
Very broad peak at 2500 - 3300cm^-1 = O-H group
Sharp peak at 1680 - 1750 cm^-1 = C=O group
What happens inside a mass spectrometer
Organic compound is vaporised and passed through the spectrometer
Some molecules lose an electron and forms molecular ions
Excess energy from the ionisation makes the bonds vibrate more
Vibration causes bond to weaken
• Molecular ion splits by fragmentation
What’s the symbol of the molecular ion
M+
Is fragmentation predictable? Why?
No
Because it can happen anywhere in the molecule
In a mass spectrometry how is a molecular ion represented
It’s the peak with the highest mass/charge ratio
The molecular mass of the molecular ion is equal to what?
Relative molecular mass of the compound
Will the molecular ion peaks of 2 isomers of the same compound be same or different
Same
What’s the m/z value of CH3+
15
What’s the m/z value of OH- from alcohol
17
What’s the m/z value of C2H5+
29
What’s the m/z value of C3H7+
43
What’s the m/z value of C4H9+
57
What are the advantages of using mass spectrometry
Cheap
Small quantities of samples required
What’s the main disadvantage of using mass spectrometry
The sample is completely destroyed
