NMR Spectroscopy Flashcards
What is NMR spectroscopy?
NSM Spectroscopy is the measurement of nuclei spin transition from excited states to relaxed states in the radio-wave frequencies.
what does the spin on a nuclei do?
a nuclei spin creates a small magnetic field around the atom
What happens to the magnetic field around a nuclei if exposed to another magnetic field?
The field can either align or oppose the foreign magnetic field, if the two fields align then the nuclei has a lower energy state, whereas if they oppose then it has a higher energy state.
What is the larmor frequency?
500mHz which is the radio frequency used on in Proton NMR. It is the energy difference between opposed and aligned in a hydrogen nuclei.
What does a large broadband of radio frequency do to the nuclei’s magnetic field?
When subjected to a radio frequency (around larmor) the nuclei absorbs the energy causing those that are aligned with the field to become excited and start opposing the field.
How do we listen for data?
We measure the radio frequency released from the nuclei as it goes from an excited state to a ground state.
How do we differentiate hydrogens from each other?
When a hydrogen is attached to a molecule its neighbouring electrical fields (density) can either provide shielding or de-shielding from the magnetic energy. These effects alter the total absorption from the applied magnetic field and subsequently a different excitation and relaxation by the hydrogen.
What happens if we attach hydrogen to a electronegative atom (electron withdrawing)?
The hydrogen will be de-shielded from its own magnetic field.
What is NMR coupling?
Nuclei that are neighbouring also have an effect on each other that can occur up to three bonds away. This is typically used for determining how many hydrogen bonds are present in a specific part of the molecule.
How many neighbouring hydrogens are there in a quartet?
3 Neighbouring Hydrogens
How many neighbouring hydrogens are there in a triplet?
2 Neighbouring Hydrogens
What do you call hydrogens that are all attached to one particular atom in relation to NMR.
Chemically equivalent
what is a chemical shift in NMR?
It is related to de-shielding effects, for example if hydrogen was attached to an oxygen the oxygen would deshield the hydrogen. The greater the chemical shift the greater the deshielding.
How do we create solutions for proton NMR?
We use deuterium as a Solvent, as this will not affect the NMR
How do we increase our NMR resolution and signal?
By taking multiple scans, this allows for the addition of multiple scans to decrease noise and increase resolution
