Organic Analysis Flashcards
When you are identifying an organic compound what do you need to know?
The functional groups present
What test would you use for an alkene? What would the result be?
Shake with bromine water
Result = orange colour disappears
What test would you use to test for a halogenoalkane? What would the result be?
Add NaOH(aq) and warm Acidify with HNO3 Add AgNO3(aq)
Result = precipitate of AgX
What test would you use for an alcohol? What would the result be?
Add acidified K2Cr2O7
Orange colour turns green with primary or secondary alcohols (also with aldehydes)
What chemical test would you use for aldehydes? What would the result be?
Warm with Fehling’s solution
or
Warm with Tollens’ solution
Result = blue colour turns red precipitate
or
Silver mirror forms
What chemical test would you use for carboxylic acid? What would the result be?
Add NaHCO3(aq)
CO2 given off
What determines which halogen is present in a halogenoalkane? (Chemical test)
Which halogen is present can be determined by the solubility of the precipitate of AgX in ammonia
A compound decolourises bromine solution and fizzes when sodium hydrogencarbonate solution is added:
a) what two functional groups does it have?
b) it’s relative molecular mass is 72. What is its structural formula?
a) alkane and carboxylic acid
b) CH2=CHCO2H
Give 2 uses of mass spectrometry
Measure the relative atomic masses of atoms.
Finding the relative molecular mass of organic compounds.
Briefly describe mass spectrometry, time of flight, and a mass spectrum.
The compound enters the mass spectrometer in solution. It is ionised and the positive ions are accelerated trough the instrument as a beam of ionised molecules. These then fly through the instrument towards a detector.
Their times of flight are measured.
The output is then presented as a graph of relative abundance against m/c ratio. However, since the charge on the ions is normally 1+, the horizontal axis is effectively relative mass. The graph is called a mass spectrum.
State what is meant by a molecular ion.
In mass spectrometry this is a molecule of the sample which has been ionised but which has not broken up during its flight through the instrument.
What is gas chromatography?
A technique for separating mixtures which uses a stream of gas to carry a mixture of vapours through a tube packed with a powdered solid. The different components of the mixture emerge from the tube at different times.
As the components emerge from the column, their amounts are measured and they are fed straight into a mass spectrometer which produces the mass spectrum of each and allows them to be identified.
So the amount and identity of each component in a complex mixture can be found.
What is high resolution mass spectrometry?
Measuring masses to three or four decimal places.
This method allows us to work out the molecular formula of the parent ion. It makes use of the fact that isotopes of atoms do not have exactly whole number atomic masses (ex. C-12, which is exactly 12 by definition).
Explain what the fingerprint region is
The area of an IR spectrum below about 1500cm^1 usually has many peaks caused by complex vibrations of the whole molecule.
This shape is unique for any particular substance.
It can be used to identify the chemical, just as people can be identified by their fingerprints.
What causes the greenhouse effect?
By gases in the atmosphere that absorb the IR radiation given off from the surface of the Earth and would otherwise be lost into space.
