I completed the A-Level in one year teaching most of the course to myself, earning an A overall. This is a summary of the textbook chapter with all details you will need for the exam, I found this most useful as it streamlines the information and keeps everything I needed in one place. Comparing ma...
Organic Analysis
16.1 Test-tube reactions: Fingerprint region: the area of the infrared spectrum
below 1500cm-1 has many peaks caused by the whole
Group test result molecule. The shape is unique to each substance, like a
C=C shake with bromine goes colourless fingerprint. Chemist compare this to a database of known
R-X 1. Add NaOH, warm compounds to identify it
2. acidify with HNO3 precipitate AgX
3. Add AgNO3
R-OH add acidified K2Cr2O7 orange>green Common Exam Questions:
R-CHO Fehlings / Tollens. Positive result
R-COH Fehlings / Tollens no change “Describe a test to confirm the presence of…”
R-COOH add NaHCO3 CO2 given off
“Explain the process of mass spectrometry”
Insoluble -> long hydrocarbon chain or a non-polar
group “What’s the fingerprint region, how is it used to identify
acidic -> a carboxylic acid? compounds?”
Solid -> long hydrocarbon chain, giant structure
“Analyse this infrared spectrum, what compound is it
for/ what functional groups does it contain”
16.2 Mass spectrometry:
“Explain a process you could use to identify a unknown
Can be used to find the atomic mass of atoms and the sample”
molecular mass of compounds. Same process occurs as
in topic 1, time of flight depend on the m/z ratio of the
ion.
The abundance of the ions is then presented on a mass
spectrum.
Fragmentation: the formation of smaller positive ions
as the larger molecular ion breaks whilst being ionised.
Each fragment is represented by a line of the spectra.
Molecular ion: the positive ion created by the full
compound, the true molecular mass.
high resolution means measuring to 3/4 decimal
places to get more accurate results for masses and
abundances.
16.3 Infrared Spectroscopy:
Works because a pair of atoms are always vibrating,
the stronger the bond the softer they vibrate, heavier
atoms vibrate more slowly. Every bond has a specific
frequency it vibrates at.
1. Shine infrared radiation through the samples
2. The radiation after the sample is missing the
frequencies that corresponds to the bonds
frequency.
3. A graph of transmittance and frequency of
radiation is plotted
The dips in the graph show the bonds that are present in
the compound
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