NMR spectroscopy NEED TO DO EXPLAINING OH PEAKS WITH MIKE

Question 1

why is CDCl3 used in proton NMr (4 marks)

Answer 1

• good solvent
• deuterium is not NMR active
• better at dissolving polar substances
• inert

Question 2

why is CCl4 used in proton NMR (4 marks)

Answer 2

• inert
• dissolves non polar substances
• good solvent
• not NMR active

Question 3

why is CHCl3 not used in proton NMR if it is a good solvent?

Answer 3

produces one large peak due to H in solution and tiny peaks for actual compounds

Question 4

why is TMS used in NMR

Answer 4

• inert
• calibrates the NMR
• very soluble in anything
• very shielded (protons)

Question 5

how many protons and how many environments are these protons in, in TMS?

Answer 5

12 protons which are all in the same environment so give a single sharp peak that can be easily identified

Question 6

how many carbons does TMS have and how many environments are these in

Answer 6

4 carbons in the same environment that will give a single sharp peak that can be easily identified

Question 7

what is an integration trace

Answer 7

the area under the peak is proportional to the number of protons that cause the absorption

Question 8

how do you calculate the number of peaks

Answer 8

number of protons in neighbouring environment + 1

n +1

Question 9

if there is 1 neighbouring proton
1. how many peaks are there?
2. what is it called?
3. give the ratio?

Answer 9

1. 2 peaks
2. doublet
3. 1:1

Question 10

if there are 2 neighbouring protons
1. how many peaks are there?
2. what is it called?
3. give the ratio?

Answer 10

1. 3 peaks
2. triplet
3. 1:2:1

Question 11

if there is 3 neighbouring proton
1. how many peaks are there?
2. what is it called?
3. give the ratio?

Answer 11

1. 4 peaks
2. quartet
3. 1:3:3:1

Question 12

if there are 4 neighbouring protons
1. how many peaks are there?
2. what is it called?
3. give the ratio?

Answer 12

1. 5 peaks
2. multiplet
3. 1:4:6:4:1

Question 13

what are the 4 steps to making an NMR spectrum for a known compound

Answer 13

1. get formula of compound
2. draw structure
3. ask census questions to carbons
4. 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)

Question 14

what 3 census questions do you ask each H atom

Answer 14

• 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)