Chromatography and Spectroscopy (Carbon-13 and hydrogen) Flashcards
Process of Gas Chromatography:
A small sample of a gaseous mixture is injected into a coiled glass elastic tube - The mixture is carried by the flow of a (noble gas) mobile phase. The mixture passes through a stationary phase (A high boiling point liquid adsorbed onto an inert solid) repeatedly. The mixture is separated due to the differing solubilities. More soluble substances diffuse more slowly across the stationary phase; This process repeats multiple coils, further seperating the substances, The gases are then detected by providing peaks at different Retention time. (Rt) Mixture them evaporate
How are substances in a mixture seperated in Gas Chromatography:
The substances are seperated due to their differing solubilities causing them to travel at different speeds through the stationary phase.
Thin Layer Chromatography: Uses
Used for colourless chemicals
Tests for water purity
Thin Layer Chromatography: Mobile Phase:
Volatile Solvent
Thin Layer Chromatography: Stationary Phase:
Silica plate with adsorbed liquid.
Gas Chromatography: Uses
Testing for drugs,
Environmental analysis
Astrochemistry
Gas Chromatography: +ves
Sensitive - small amounts of sample required
Good seperation of substances
Gas Chromatography: Mobile Phase
Inert gases
Gas Chromatography: Stationary Phase
High boiling point liquid adsorbed onto inert solid.
Gas Chromatography: Calculating Concentration:
Relative abundance is used to calculate the concentration with the use of a calibration curve.
Chemical shift range outside of 220pm on a Carbon-13 NMR represents what?:
Solvent, concentrations and substituents.
What is the finger print on an IR-spectroscopy:
Before 1500 cm^-1 contains unique peaks used to identify particular molecule.
C-13 NMR: Symmetrical carbons in a molecule_________
Symmetrical carbons in a molecule contribute to the same peak.
Peak height is determined by what?
Relative abundance
What are the labile groups? (proton NMR)
NH and OH, because they can dissociate in solvents. Produce a singlet on spectrum
What is TMS?
(Tetramethylsilane) is chemically inert and soluble in most solvents and acts as a reference compound (0 chemical shift)
Spin-Spin coupling:
the number of lines in a peak caused by the number of protons in the neighbouring environment.
What are the +ve’s of a higher resolution NMR spectrum?
Different chemical shifts provide the different types of proton environments.
Number of peak areas and ‘n+1’ rule show the number of protons in environments.
D20 can be used to identify labile OH and NH groups
True or false: Deshielding only affects proton NMR.
False
How does deshielding affect NMR?
Deshielding affects both carbon and proton NMR, shifting their peaks to a greater chemical shift within their range.
Why does deshielding occur?
An electronegative element attracts the electrons of another atom away from their nucleus. This exposes the nucleus to more of the external magnetic field
Qualitative Analysis: Alkene
Add Bromine water and it will be decolourised from orange to colourless
Qualitative Analysis: Haloalkane
Add silver nitrate and ethanol in a 50’C water bath
Qualitative Analysis: Carbonyl
Add 2,4-dinitrophenylhydrazine ~ Orange precipitation
Qualitative Analysis: Aldehyde
Add tollens’ reagent and warm ~ silver mirror
Qualitative Analysis: Carboxylic Acid
Add aqueous sodium carbonate ~ effervescence
Qualitative Analysis: Primary/Secondary alcohol and aldehyde
Add acidified potassium dichromate and warm in a water bath. (Colour change from orange to green)
Use of deuterated solvents in proton NMR:
Prevents solvent from interfering with NMR spectrum.
