NMR spectroscopy NEED TO DO EXPLAINING OH PEAKS WITH MIKE
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why is CDCl3 used in proton NMr (4 marks)
• good solvent • deuterium is not NMR active • better at dissolving polar substances • inert
why is CCl4 used in proton NMR (4 marks)
• inert • dissolves non polar substances • good solvent • not NMR active
why is CHCl3 not used in proton NMR if it is a good solvent?
produces one large peak due to H in solution and tiny peaks for actual compounds
why is TMS used in NMR
• inert • calibrates the NMR • very soluble in anything • very shielded (protons)
how many protons and how many environments are these protons in, in TMS?
12 protons which are all in the same environment so give a single sharp peak that can be easily identified
how many carbons does TMS have and how many environments are these in
4 carbons in the same environment that will give a single sharp peak that can be easily identified
what is an integration trace
the area under the peak is proportional to the number of protons that cause the absorption
how do you calculate the number of peaks
number of protons in neighbouring environment + 1 n +1
if there is 1 neighbouring proton 1. how many peaks are there? 2. what is it called? 3. give the ratio?
• 2 peaks • doublet • 1:1
if there are 2 neighbouring protons 1. how many peaks are there? 2. what is it called? 3. give the ratio?
• 3 peaks • triplet • 1:2:1
if there is 3 neighbouring proton 1. how many peaks are there? 2. what is it called? 3. give the ratio?
• 4 peaks • quartet • 1:3:3:1
if there are 4 neighbouring protons 1. how many peaks are there? 2. what is it called? 3. give the ratio?
• 5 peaks • multiplet • 1:4:6:4:1
what are the 4 steps to making an NMR spectrum for a known compound
• get formula of compound • draw structure • ask census questions to carbons • work out what spectra would look like where would you place stuff due to it being electronegative (as these are shifted further to the left)
what 3 census questions do you ask each H atom
• describe position of an atom which it lives (shift) • how many H are on that atom (integration number) • say how many chemically different hydrogen atoms live on adjacent/neighbour atoms (number of peaks = n + 1)