Chapter 29 - Chromatography And Spectoscopy Flashcards
What does thin layer chromatography do?
Shows how many components are in a mixture
How do you set up a TLC plate?
A thin sheet of plastic or glass coated with silica
What is the stationary phase in TLC?
The adsorbent
What is adsorption?
Silica holds the different compounds in the mixture to its surface
How do you calculate the retention factor?
Distance moved by component / distance moved by solvent
What is the stationary phase in gas chromatography?
A high boiling liquid adsorbed onto a solid support
What is the mobile phase in gas chromatography?
An inert gas carrier
Process of gas chromatography
Mixture is injected into gas chromatograph
Gas carrier carries mixture through stationary phase
Components slow down
Components are separated depending on their solubility in the stationary phase
What does the peak integration show us?
The concentrations of components in a sample
How to test for a carbonyl?
Add 2,4-dinitrophenylhydrazine and an orange precipitate will occur
How to test for an aldehyde?
Add Tollen’s reagent and warm
A silver mirror effect occurs
How to identify a carboxylic acid?
Add sodium carbonate and it will effervesce
What can NMR be used to identify?
Isotopes with an odd number of nucleons
What is resonance?
A strong magnetic field and radiation allow the nucleus to absorb so much energy that the electrons flip between spin states
What chemical is used as the standard for chemical shifts?
Tetramethylsilane
What is a deuterated solvent?
The 1H atoms have been replaced by 2H atoms (deuterium)
Why are chemicals deuterated?
Deuterium produces no NMR signal
What two pieces of information can be deduced from a carbon NMR spectrum?
The number of different carbon environments
The different types of carbon environment
What will carbon atoms in different environments do?
Absorb radiation at different chemical shifts
What information can be deduced from proton NMR?
The number of each type of proton environment
The number of each type of proton
What does it mean when two protons are equivalent?
They will absorb at the same chemical shift
What does the integration trace on a proton NMR tell you?
The number of protons responsible for each peak
What is the n+1 rule?
For a proton attached to carbon atom with n protons, the number of peaks in the splitting pattern will be n+1
Why is it difficult to identify NH groups and OH groups from a spectrum?
The peaks are broad and of variable chemical shift
How are OH and NH groups identified from a spectrum?
NMR is run as normal
D2O is added and the spectrum repeated
Deuterium replaces the OH and NH groups
As deuterium doesn’t absorb in the range we study, the OH peak essentially disappears
