Unit 9 Flashcards
Vibrational + NMR
Where in the spectrum is the energy needed to make bonds vibrate
infrared
What ways can bonds vibrate?
symmetric, asymmetric and bend
Are vibration levels quantised?
yes, incoming radiation must match the energy difference between energy levels
what does an infrared spectrometer do?
it measures which energy is absorbed and how much
how will the pen move when there is more absorbance?
it will move down. Each peak is caused by a bond and energy used to make it vibrate
What is a group frequency?
its a range of frequencies eg the 1/wavelength number which correlate to functional groups
Alcohol group frequency? (o-H) (c-o)
3300 and 1050
Carbonyl group frequency? (c=o)
1720-1750
Ester group frequency? (c-o)
1070-1150
Acids group frequency? (o-h)
2500-3000
Nitriles group frequency? (triple bond c-n)
2000-2500
Where will a strong bond be on a IR spectra and why?
It will be at a high wavenumber as this is proportional to frequency. A strong bond will need more energy to make it vibrate and more energy means a higher frequency.
Where will a weak bond be on an IR spectra?
It will have a low wavenumber as it doesn’t need a high frequency to vibrate the bond
Protons have spins and are like magnets, their magnetic field will try to line up if in a magnetic field. T or F
T
Can you cause protons to be in different spin states?
Yes by giving them radio wave energy and an applied magnetic field
What has more energy a proton aligned against the field or with it?
against the field
What does NMR detect?
Change in spin
What does a peak in NMR represent?
Different hydrogen environments. The different conditions mean they need different energies to move them
What does the height of a NMR peak tell us?
How many hydrogens are in that environment, the ratio between peaks tells you not the actual height.
Why should you ignore an NMR peak if its at 0?
Because that is the standard for comparison called TMS
What does splitting tell you on a NMR spectrum ?
It tells you the number of other hydrogens next to the one you’re looking at. It follows the n+1 rule
What is an equivalent hydrogen atom in NMR
A hydrogen attached to the same carbon wont have any affect. Also, if a hydrogen on another atom is in exactly the same environment it is also equivalent
How can you work out the split ratio?
you can use pascals triangle. Just do 1 1 + 1 1+2+1 make sure you add ones at edge 1 + 3+ 3+ 1 1+4+6+4+1 1+5+10+10+5+1 can keep going
How do you work out pascals triangle and what can you use it for ?
Can use it to work out the split ratio in NMR 1 1 + 1 1+2+1 make sure you add ones at edge 1 + 3+ 3+ 1 1+4+6+4+1 1+5+10+10+5+1 can keep going
What does a strong signal at 3000 and 1720 on IR indicate?
A carboxylic acid
What is wavenumber?
its 1/wavelength
what does infrared spectroscopy measure?
The absorption of IR
What is IR absorbed for in molecules?
used to increase vibrations of the bonds in molecules but the incoming energy must match the difference between vibrational energy levels
In NMR what is radio wave energy used for?
change the spin state of protons to a higher spin state
