Organic analysis Flashcards
How do you test for alkenes? What is the result?
Shake with bromine water, result is bromine water is decolourised (orange to colourless)
How do you test for haloalkanes? What is the result?
Add NaOH (aq) and warm, acidify with HNO3, add AgNO3(aq) Result: precipitate of AgX (for Cl=white, for Br=cream, for I=yellow)
What is mass spectrometry? How does it work?
Used to find the relative molecular masses of organic compounds.
- Compound is dissolved in solution, ionised by a high voltage supply (to mostly 1+ ions)
- accelerated by a negatively charged plate, becomes a beam of ionised molecules
- reaches detector and cause a current to flow. Time of flight used to work out m/z value and plot graph.
What does the x axis show on a mass spectrum?
What does this effectively show and why?
Shows m/z value (mass divided by ionic charge).
Since most ions are 1+, this effectively shows Mr
Why are there multiple peaks when molecules are put into a mass spectrometer?
The molecular ion is shown as a peak, but it will also FRAGMENT into smaller molecules, so these peaks are shown as well
Also, due to isotopes of atoms, different peaks may be seen
How does gas chromatography work and what does it tell you?
A stream of gas carries a mixture of vapours through a column packed with solids, different compounds move through at different speeds, so they are separated. The amount of each compound can then be measured
What does GCMS stand for?
Gas chromatography linked to mass spectrometry
What might GCMS be used
for?
Powerful chemical analysis - forensic work, measuring water pollution, drug testing on athletes, racehorses
What is high resolution mass spectrometry?
Mass spectrometers which give Mr to 3d.p. or 4d.p. are called high resolution (low resolution is to nearest whole number)
What does high resolution mass spec allow you to do?
Distinguish between compounds that have the same Mr to the nearest whole number, but are made up of different atoms and therefore have different values of Mr to 3.d.p
Why do atoms and chemical bonds absorb infrared
radiation?
They are constantly vibrating - they can absorb infrared radiation that is the same frequency as their frequency of vibration
What effect does a stronger bond have on the frequency of vibration?
Vibrate faster (with higher frequency)
What effect do heavier atoms have on the frequency of vibration?
Vibrate slower (with lower frequency)
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 happens inside an infrared spectrometer?
Beam of infrared radiation with a range of frequencies is passed through the sample
Radiation that emerges is missing frequencies that have been absorbed by the bonds in the sample
Graph is plotted of intensity against frequency of radiation
