RPA - Analysis Flashcards
what is the stationary and mobile phase in TLC?
Stationary - silica plate
Mobile - solvent appropriate for compound
What is the stationary and mobile phase in GC?
stationary - solid on solid support (tube)
Mobile - carrier gas
What is the stationary and mobile phase in gas-liquid chromatography?
Stationary - liquid on solid support
mobile - carrier gas
What can we infer from the peak height of H1 NMR?
The relative intensity shows how many hydrogens are in each environment
Which groups do not exhibit splitting?
-OH,-NH, COOH groups
What technique can we use to identify -OH/-NH groups?
Run a second NMR with D2O, which exchanges protons with the OH/NH groups using labile protons, so does not show up on the second run.
What solvent is commonly used in both C13 and H1 NMR? Why
CDCl3. It is unreactive, volatile, and does not show up on H1 NMR, and shows one peak on C13, which is normally removed.
What is the standard used in NMR, why do we use it, and what makes it good at its job?
TMS (Tetramethylsilane) is the standard, because it produces a high peak of relative intensity 12, which is a single peak, due to the hydrogens in equivalent environment. THis is normally added to calibrate the machine, as TMS should have a ppm value of 0. It is unreactive, and volatile so can be removed easily from the sample to make the analysis non-destructive.
What is the group next to a hydrogen environment showing splitting of 4 (quartet)
CH3, using the n+1 rule,.
What happens if a triplet and quartet are spotted in H1 NMR?
They are likely to be CH2-CH3 next to each other, as they give each other the splitting pattern. This is common in ester groups containing O-CH2-CH3.
How should you lay out answers to NMR analysis questions?
In a table - ppm-environment-splitting-inference from splitting-integration.
How are components separated in TLC?
Adsorbtion
How are components separated in a liquid stationary phase e.g. GLC?
relative solubility
Which groups do not split?
NH, OH, COOH
When identifying splitting patterns, how do you describe the adjacent group e.g. for quartet?
splitting of 4, hence three adjacent hydrogens using n+1 rule, hence CH3 group.
If there are two different groups attached to aromatic ring, and 4 carbon-13 peaks, which positions are the groups in?
1,4
Give seven marks worth of things you can find from high resolution H1 NMR
Shift - environment
#peaks - total # environments
splitting - adjacent hydrogens
integration - relative # protons in environment
D2O - removes peaks due to OH/NH
n+1 rule - refers to splitting where n=number of adjacent hydrogens and n+1 = #peaks observed.
