NMR

Question 1

what does NMR stand for ?

Answer 1

• nuclear magnetic resonance spectroscopy

Question 2

what does Carbon 13 NMR tell us about the molecule?

Answer 2

• gives us info about how carbon atoms are arranged in a molecule

Question 3

what does proton NMR tell us about the molecule ?

Answer 3

• gives us info about how hydrogen atoms are arranged in a molecule

Question 4

what does NMR investigate ?

Answer 4

• it investigates atoms with an odd number of nucleons
  (protons and neutrons in the nucleus)
• so these nuclei spin
• so they interact with magnetic fields

Question 5

What must a solvent not do?

Answer 5

• Solvent should not interfere with the spectrum -
• solvent must not dissolve the sample you want to analyse

Question 6

What must the solvent not contain?

Answer 6

• Solvent must not contain any protons

Question 7

Why must the solvent not contain any of these?

Answer 7

• Any protons in the solvent would create a peak and add to the spectrum
• you wouldn’t know it the peak came from the solvent or the sample

Question 8

What are 2 typer of samples you might want to analyse?

Answer 8

• A polar sample
• non-polar sample

Question 9

What kind of solvents must polar solvents dissolve in?

Answer 9

• Polar solvent and vice verse

Question 10

What is an example of a polar solvent?

Answer 10

• CD CL 3

Question 11

What is meant by D in CD CL 3? And what are its properties?

Answer 11

• Deuterium
• the atoms have no nuclear spin
• it is an isotope of hydrogen containing I neutron in its nucleus

Question 12

What is an example of a non-polar solvent?

Answer 12

• Tetra chioromethane

Question 13

Why is tetrachloromethane ( CCI4 ) non-polar it in contains a highly electronegative atom?

Answer 13

• It has a symmetrical tetrahedral shape so no dipole interactions are made

Question 14

How do we calibrate a spectrum?

Answer 14

• A small quantity of TMS is added to samples

Question 15

Why is TMS added to samples?

Answer 15

• Because it produces a single peak providing a standard to which other peaks are compared to

Question 16

What are the properties of TMS that are useful in calibration?

Answer 16

• Only given 1 signal
• it is non-toxic
• it is inert
• has a low boiling point (26 degrees)so can be easily removed from the sample afterwards = volatile
• gives a signal that is Further right than most of the signals from organic compounds due to low electronegativity of si

Question 17

What do highly electronegative atoms do to the chemical shift value and why?

Answer 17

• Give a larger value
• their atoms deshield the nucleus
• so the larger the chemical shift the closer to an electronegative atom