Flashcards
6.3.2 Spectrometry
Cards in this deck (19)
- 1What does NMR stand for?Nuclear Magnetic Resonance
- 2What are the basic principles of NMR?You can find the structures of complex molecules by placing them in a magnetic field and applying EM waves of radio frequency to them. If radio waves of the right frequency are absorbed, the nuclei flips from parallel to applied magnetic to field to anti-parallel. This energy change can be monitored and recorded. Uses the resonance of nuclei with spin.
- 3Give one use of NMR?MRI scans
- 4What kind of nuclei does NMR work with (and examples)?Those with an uneven number of nucleons, meaning they will spin e.g. 1H, 13C
- 5Summarise what these mean for 13C NMR: Number of signals Area under peak SplittingNumber of signals: One signal for lachcarbon environment (each set of inequivalent 13C atoms)
Area under peak: no meaning
Splitting: there is no splitting for 13C NMR - 6Why is it easier to get a spectrum of 1H NMR than 13C NMR?Most H atoms are 1H- it is much more abundant than 13C. This means almost all H atoms have spin so show up
- 7On a low resolution spectrum, what peaks would you expect to see for H NMR?One peak for each set of inequivalent H atoms (each chemical environment shows 1 peak)
- 8What does the area under the peak represent (for H NMR)?The area under the peak is proportional to the number of 1H atoms represented by the peak
- 9What is the integration trace?A stepped line that makes it easier to measure the area under the curve (height of line = area under that peak)
- 10What is TMS (name and structure)?Tetramethylsilane
- 11Why is TMS used?The signal due to tetramethylsilane, TMS, is adjusted to read zero on the spectrum. All other measurements are then taken as parts per million (ppm) shift of the absorbance when compared to this value.
- 12What are other advantages of using TMS?Inert, non-toxic, easy to remove from the sample (as relatively volatile)
- 13When does splitting/spin-spin coupling occur?Neighbouring hydrogen atoms (3 or fewer bonds away, or on the adjacent carbon) affect the magnetic field of 1H atoms and causes their peaks to split
- 14What is the n+1 rule?If there are n inequivalent 1H atoms on the neighbouring carbon then the peak will split into (n+1) smaller peaks
- 15Draw the splitting patterns for 0, 1, 2 and 3 inequivalent H atoms 3 bonds or less away.
- 16Why must solvents used for 1H NMR not contain any hydrogen atoms?Signals from the solvent would swamp signals from the sample, as there is much more solvent than sample.
- 17Which solvents are used?Deuterated solvents: CDCl3, D2O, C6D6 CCl4 - tetrachloromethane
- 18Summarise what these indicate for 1H NMR: Number of signals Splitting Area under peakNumber of signals: One main signal for each set of inequivalent 1H atoms (for each hydrogen environment)
Splitting: Number of smaller peaks = 1 + number of inequivalent hydrogen atoms 3
bonds away
Area under peak: Proportional to the number of atoms represented by that peak - 19Why does the peak from O-H bonds disappear if D2O is used as a solvent?O-D bond is formed in preference to O-H due to labile protons that move/swap from one molecule to another.
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- A level Chemistry (Module 6 – Organic Chemistry & Analysis) Flashcards on 6.3.2 Spectrometry, created by Aania Bokhari on 06/03/2019.
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