29 Chromatography and spectroscopy Flashcards
What is gas chromatography (GC) used for?
To separate volatile liquids.
What happens in gas chromatography (GC)?
- A small amount of the volatile mixture is injected into the apparatus
- The mobile carrier gas carries the components through the column (inside a thermostatically controlled oven) where it separates into different liquids
- Slower it moves–> greater affinity with stationary phase
- Produces a chromatagram
What is the mobile phase of GC?
An inert gas (e.g. nitrogen)
Wat is the stationary phase of GC?
Solid/ high boiling point liquid coated on a solid support
What do the number of peaks on a GC chromatogram represent?
The number of substances in the mixture.
What does the area under each peak represent on a GC chromatogram?
The relative amount of the substance in the mixture
What is the test for an alkene?
Add bromine water
Orange –> colourless
What is the test for the halogens?
Add silver nitrate and ethanol at 50 degrees
Chloro- white
Bromo- Cream
Iodo- Yellow
What is the test for a carbonyl group?
Add 2,4-DNP
Orange precipitate
What is the test for an aldehyde group?
Add Tollens reagent + warm
Silver mirror
What is the test for a primary/secondary alcohol?
Add K2Cr2O7 + warm
Orange –> Green
What is the test for a carboxylic acid?
Add NaCO3 (aq)
Fizzing
What is the test for a phenol?
Bromine water
White precipitate
What is resonance?
When the nucleus can absorb energy and rapidly flip between the two spin states.
What is used in a NMR spectrometer?
A super-conducting electromagnet, cooled by liquid helium.
What is chemical shift in NMR?
When the electrons in atoms shift the energy and radio frequency needed for NMR.
What is the unit for chemical shift?
ppm
What substance is used as a standard reference in NMR?
TMS- has a chemical shift of 0ppm
What happens when deuterium oxide is added to a H NMR spectrum reading, and why?
Any O-H or N-H peaks disappear, because the hydrogen gets replaced by a D, meaning it isn’t detected.
What do the areas under a proton NMR spectra tell us?
The relative number of each type of proton.
What is the splitting rule in proton NMR?
For a proton with n protons attached to an adjacent carbon atom, the number of sub-peaks in a splitting pattern is n+1.
What is the chemical environment of a carbon determined by?
The position of the atom within the molecule and symmetry.
