3.15 NMR spectroscopy Flashcards
What are the two main types of NMR
13C NMR - tells us information on how carbon atoms are arranged
1H NMR - tells us how hydrogen atoms are arranged
How does a nucleus get a spin and what does this spin do
- Atom has nuclear spin if it has odd nucleon number
- nuclear spin creates a weak magentic field. NMR detects how these magnetic fields are affected by a larger external magnetic field
Describe the motion of nuclei spin
- spin in random direction, unless an external magnetic force is applied
- nuclei either spin in the direction of the magnetic field or against it
- Those that spin in the direction of the magnetic field have a lower energy
How can nuclei jump up to a higher energy level
b) can nuclei jump to a lower energy level
NMR fires out radio waves
At specific frequency the nuclei that are aligned with the magnetic field absorb the energy and flip to another level
b) Yes and they emit radio waves
What does NMR measure
Amount of energy absorbed
How is shielding of a nucleus from a magnetic field affected
- can be shielded from electrons
- electronegative element such as oxygen near a carbon atom, would reduce the shielding of the carbon atom
What does the effect of the magnetic field on the nuclei depend on
- will be felt differently depending on the environment, as they absorb different energies
- NMR measures the difference
What does the environment depend on
environment determined by group of atoms that exist near nuclei, we look along full chain
How can atoms be in the same environment
bonded to an atom or group of atoms that are identical
For the first two, identify number of carbon environments
For the last two, identify number of hydrogen environments
What chemical do we use as a standard when looking at chemical shift in NMR spectra and why
What is the chemical shift
What do the two peaks represent
State how many different carbon environments there are. Label three carbon atom with the peak on the graph
Label peaks with hydrogen atom
What does it mean to have a
singlet peak
doublet peak
triplet peak
quarlet peak
singlet - 0 hydrogens on adjacent carbon
doublet - 1 hydrogen on adjacent carbon
triplet - 2 hydrogens on adjacent carbon
quarlet peak - 3 hydrogens on adjacent carbon
State split number of peaks
Number of neighboring hydrogens
Relative size
a) draw structure of K which has only one peak in its proton n.m.r spectrum
b) draw structure of an isomer of L which has only only two peaks in the proton n.m.r spectrum
A) all hydrogens must be the same as there is only one environment
B) there must be two environments
A = singlet
B = triplet
Q is C4H7CLO
Tetramethylsilane is the second answer
