NMR Flashcards
What is NMR
Nuclear Magnetic Resonance Spectroscopy
What atoms behave if they are spinning
Hydrogen
Carbon
Nitrogen
Fluorine
Why do atoms spin
They possess a magnetic moment so the nuclei behave as little magnets
What happens to the spin state when there is a lack of external influence
The spin state adopted by the nucleus is of the lowest energy state
What happens to the spins of a nuclei when in a magnetic field
the spins precess their alignment, meaning it rotates on an axis different from its alignment.
When removed from a magnetic field what occurs to the precessed spin states
they return back to their preferred spin state
What are the 3 main things is NMR used for
Used to gain information about
- 3d structure of molecules
- topology of molecules
- dynamic behavior in solid state
Describe the two alignment state that a hydrogen nucleus can have in an external magnetic field
Aligned
or
Opposed
By supplying energy to the nuclei what happens to its alignment
By providing the correct amount of energy the alignment can flip from stable to unstable.
What is the preferred state known as
Ground State
What is the unstable state known as
Excited State
What is relaxation
Processes by which an excited magnetic state returns to its equilibrium distribution
What measures Relaxation
Rf detector
What is the output detected by the Rf detector
Hint* FID
Free inductive decay
What is resonance condition
flipping of the proton from one magnetic alignment to the other by radio waves
What does a bigger B0 mean
bigger difference in energy between the spin states therefore more sensitive instrument
What is normal state of compounds used for NMR
solutions
Why are deuterated solvents used
to minimize interference from proton signals in the solvent
What is B0
applied external magnetic field
What is BE
induced magnetic field
Why do 1H nuclei resonate at sleightly different values depending on precise chem environment
Induced magnetic field from the orbit of electron which opposes the external field. This is due to shielding and thus alters the value very slightly.
What do peaks on a NMR graph mean
it shows chemical shift of the functional groups
What does the area under the peak tell us (integration)
how many protons are in each chemical environment
What do the relative heights of the integrals indicate
relative number of protons represent in each chemical environment
What does the splitting of each groups of peaks tell us
relationships of groups of protons to one another and is known as spin spin coupling
