Flashcards
Analysis and spectroscopy
Flashcards do conjunto (30)
- 1Why do we use TMS as a reference frequency?1. It contains both Hydrogen and Carbon so can be used to reference both atoms
2. Every single carbon and hydrogen atoms are in the same environments; so there will only be one peak
3. It is non-toxic and is easily removed due to volitality
4. It doesn't influence the chemicals - 2TOP TIPThe chemical shift is showing you how DIFFERENT the absorbtion peaks of your substance is from TMS
BONUS TIP; you know how C12 is like a reference because its Mr is basically 12.0, TMS is like the C12 of NMR - 3TOP TIP!-The area under peak shows you how many atoms in the environment
-Remember that the proportion of H to C is highhhhhhh
-Because the chances of getting C13 is like 1/100 the peak areas will be way lower than the hydrogen ones
-This is just a nifty way to distinguish the two from the same graph - 4What do chemical shift table s tell you about the structures of your moleculeDepending on what peaks you have, the table will show you what potential structures (whether carbon of hydrogen based) could be causing those peaks
- 5TOP TIP!The more electronegative the group or the closer groups are to electronegative groups like Cl or OH, the further to the LEFT the shifts
- 6Distinguish between C13 qand prton NMRC13 looks at the different carbon environments whereas proton NMR looks at the different hydrogen environments
- 7What type of atoms can be detected by NMR?NMR is very exclusive! It will only detect atoms with an odd mass and therefore a spin
- 8What does the number of peaks in NMR tell you?The number of peaks tells you the number of environments a molecule has
- 9What do the areas under the peaks in NMR tell us?The area tells us the ratio of number of atoms in that environment compared to others.
- 10How would you find out the exact numwr of atoms in a particular environment?If the molecular formular is give, see how many atoms you have that correlates to the graph (i.e if H NMR then look at hydrogen atoms)
Add all the ratios together and divide the molecular number of atoms by the sum of ratios.
Then multiply each ratio by this answer to get the actual number. - 11What can we gain from low resolution NMR compared to high resolution?-Low resolution is good at showing you how many different environments there are
-High resolution gives you more detail; the splitting patterns show you what each environment is surrounded by - 12TOP TIP!Remember that you have to look at both sides of the group to see if they are in the same environment
- 13What do the number of peaks show?The number of different environments in a molecule
- 14How can you find out, from a spectrum, how many carbon environments there are?This has been an exam question!
You have to count the number of peaks - 15TOP TIP!If you can't see a line of symmetry in a molecule, every carbon atom would be in a different environment.
- 16TOP TIP!Before investigating, make sure you have all the information you need! If you need to draw in extra H then so be it!
- 17TOP TIP!If they don't give you the molecular formula to start with, it might be a good idea to try and look for the environment with the lowest number of hydrogens and work from there....it just might be easiest
- 18What are the laws that you will always need to use when1) The neighbour rule
2) The number of peaks rule
3) The ratio rule - 19What are the two phases in chromotographyMobile phase (solvent)
Stationary phase (solid/ supported liquid) - 20Outline the method of thin layer chromatography1. Draw a thin line about 1 cm from edge of paper (using pencil)
2. On the pencil line, place a spot of ink
3. Place the paper in the solvent, ensuring that there isn't enough to cover the pencil line
4. Mark the position of the ink with pencil and calculate Rf value - 21What is the main factor which affects Rf value?The attraction between the spots and the stationary phase.....this special attraction is called adsorption.
The stronger the adsorption, the smaller the Rf value - 22What is the main differences between gas and TLC chromatography? (2)-The phases are in different states
-The retention time/ time taken to be detected in measured on gas but the distance travelled in measured by TLC - 23How does gas chromatography work?Coat the inside of tubes with you stationary phase (liquid e.g oil or solid)
-Inject the tested gas into a carrier gas stream (e.g. He)
-The different molecules will have different solubility/ adsorption with the stationary phase.
-The greater the attraction the longer the retention time - 24Cool, so I've got the different components of my substance, but how do I know which has greater proportion (in both types of chromatography)TLC; The darker the spots, the greater the proportion
Gas; the fatter/ the peaks, the greater the proportion (area= amount) - 25State (if you can) two disadvantages to gas chromatography.1. Similar structured molecules may have similar retention times
2. You can only really identify products if they have already been tested/ have a reference - 26Suggest one way to improve the accuracy of data collected from gas chromatography.-You could combine techniques with mass spectroscopy, to rule out any problems with similar molecules having similar retention times
- 27TOP TIPUse the key term....ADSORPTION, when talking about differences in Rf values
- 28Explain why substances separate in gas chromatographyThis is because of the differences between solubility of the stationary phase
- 29Explain why mass spectrometry and gas chromatography are like teh best of friends-GC can separated the components really well and MS is really good at identifying said components
- 30Discuss GC-MSThis is Gas Chromatography-Mass Spectroscopy
-This is when the two techniques are joined together making the ultimate accurate hybrid
-The separated substances from the GC go straight to the MS for identification
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- A level Chemistry FlashCards sobre Analysis and spectroscopy, criado por Sparkle Shine em 09-03-2018.
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- Sparkle Shine
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