Structure Determination Flashcards
When do nuclei have spin?
When they have an odd mass number.
How can you change a nuclei’s spin?
Change magnetic field strength or let them absorb energy through radio waves.
What is chemical shift measured in?
ppm, parts per million
What is the reference compound in NMR?
TMS
Why is TMS used as a reference in NMR?
It has C and H in the same environments and they are electron rich of will produce a peak far upfield.
What causes samples to be shifted downfield in NMR?
Shielding from electrons be it by bonding or electronegative pull.
What does spin-spin coupling show in HNMR?
Neighbouring non-equivalent hydrogens on carbons.
How can you work out the number of neighbouring non-equivalent hydrogens in high resolution HMNR?
Peaks are split into the number of neighbouring hydrogens +1 (n+1 rule)
What solvents are used in NMR?
CCl3, CDCl3, D2O
What does integration of HNMR tell us?
The proportion of the number of hydrogens in peak is due to. (Ratio of hydrogens in each environment)
What solvent must be used with esters and why?
CCl4 because it is non polar and esters do not dissolve in polar compounds
What is the mobile phase?
It is part which carries the soluble components of the mixture with it.
What is the stationary phase?
It is the part which will hold back the components in the mixture.
Why is TLC better than paper chromatography?
Faster
Small amounts used
Plates more robust than paper
What is the stationary phase in column chromatography?
Silica or alumina powder
