topic 19: spectroscopy and chromatography
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what are the different types radiation in a molecule
infrared in analysis microwaves for heating radiowaves in NMR ultraviolet in initiation of reactions
when does the NMR spectroscopy involve
involves interaction of materials with the low- energy radiowave region of the electromagnetic spectrum
what so the radiowaves used in the proton NMR cause
causes the hydrogen nucleus to change its spin state
NMR use the same technology as what
magnetic resonance imaging (MRI)
in an hydrogen NMR spectrum what does one signal represent
each set of equivalent H atoms eg. ethanol has 3 groups of different hydrogen atoms
in H NMR, what is the intensity (integration value) of each signal proportional to
the number of the equivalent H atoms it represents
in H NMR, what are the solvents used
solvents without any 1H atoms eg. CCl4, CDCl3
the solvent used dont have 1H atoms what does this mean
this means that in the H NMR the solvent will not give any peaks
state the use of CCl4 as a solvent
a non polar compound compound that is a good solvent for non-polar organic molecules
what the use of CDCl3
a polar covalent molecule that is a good solvent for polar organic molecules
a small amount of what solution is added to the sample to calibrate the spectrum
TMS (tetramethylsilane)
why is tetramethylsilane (TMS) used
*its signal is away from all the others *it only gives one signal *gives strong signal so only a small amount needed *it is non-toxic *it is inert *it has a low boiling point and so can be removed from sample easily
the spectra is recorded on what scale and what does it do
the chemical shift (δ), which is how much the field has shifted away from the field for TMS
what is δ a measure in
parts per million (ppm)
what is the δ a scale of
a relative scale of how far the frequency of the proton signal has shifted away from that for TMS
what does the δ depend on
what other atoms/groups are near the H – more electronegative groups gives a greater shift
splitting of peaks
= number of inequivalent H’s on neighbouring C atoms + 1
describe singlet
• 1 splitting peak • 0 neighbouring inequivalent H atoms
describe doublet
• 2 splitting peaks • 1 neighbouring inequivalent H atoms • 1:1 —> relative size
describe triplet
• 3 splitting peaks • 2 neighbouring inequivalent H atoms • 1:2:1 —> relative size
describe quartet
• 4 splitting peaks • 3 neighbouring inequivalent H atoms • 1:3:3:1 —> relative size
describe quintet
• 5 splitting peaks • 4 neighbouring inequivalent H atoms • 1:4:6:4:1 —> relative size
what is it called when there is more than 5 splitting peaks
multiplet
what is chromatography
an analytical technique that separates components in a mixture between a mobile phase and a stationary phase