Flashcards
Option A - Analytical Chemistry
Cards in this deck (10)
- 1What does NMR measure?1. The number of different ^1H environments in the molecule
2.The ratio of each 1H (H ones) in each environments - 2What do the graphs have for NMR on their axis?Chemical shift on x
Absorption on y
The number of peaks on the graph shows the number of 1H environments - 3What is area under a NMR graph representative of?The ratio of 1H in each environment
- 4What are the uses of NMR spectroscopy?1. STRUCTURAL DETERMINATION
Information can be gained on the precise chemical environment of all the protons in the molecule. It can be used to distinguish between cis and trans-isomers in organometallic compounds
2. MEDICINAL USE - MRI
As the radio waves are completely harmless, NMR can be used to obtain body images of soft tissue, as the protons in water/lipids/carbohydrates give different signals
It can be used to diagnose and monitor conditions such as cancer and MS - 5What are the benefits of using tetramethylsilane as the standard reference in NMR spectroscopy?1. All the protons are in the same environment, giving a single peak
2. Its not toxic or reactive - won't interfere with the sample
3. It absorbs upfield - well away from most other protons
4. It's volatile so can easily be removed from the sample - 6What are splitting patterns in an 1HNMR spectrum made by?Spin - spin coupling
- 7How can the pattern for splitting be deduced in 1HNMR spectrums?Use pascals triangle and it looks like the shape of the splitting
- 8What are the main features of a 1HNMR spectrum?1. Number of different absorptions (PEAKS)
The number of peaks shows the number of different proton environments
2. Area under each peak
Shows the number of hydrogen atoms in that chemical environment
3. The chemical shift
Values are in the data booklet, but it is to do with how neighbouring atoms can exert shielding affects to the spinning electrons creating their own magnetic fields
4. The splitting pattern
To do with the number of protons bonded to adjacent carbon atoms. The spin spin coupling shows up on the high resolution 1HNMR as splitting patterns - 9What is needed for 1HNMR spectroscopy?*NMR involves interactions of NUCLEI (not electrons) with electromagnetic radiation
*NMR is concerned with nuclei of uneven mass numbers
* In the presence of a magnetic field, spins have different orientations with small differences in every as they line up with or against the magnetic field. The difference in energy corresponds to radio frequencies
*The sample (liquid or in solution) and reference are put into a tube that is then placed between the poles of an electromagnet
*A probe coil, radio frequency generator and receiver surrounds the sample - 10What is changed to obtain an 1HNMR spectrum?Varying the strength of the magnetic field
OR
Varying the radio frequency
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- IB Chemistry Flashcards on Option A - Analytical Chemistry, created by P H on 07/01/2015.
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- P H
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