Spectroscopic techniques

Question 1

X-ray diffraction.

Answer 1

Electron density plot shows position of atoms. H atoms not detected due to minimal electron density around them.

Pros: Gives location of all atoms
Cons: Needs good quality crystals, H undetected

Question 2

Mass spectrometry

Answer 2

Gives mass of sample molecules, plus information about bonding from fragments

Pros: Gives molecular formula, good for mixture analysis, tiny sample needed
Cons: Difficult to interpret when unknown

Question 3

Mass spectrometry

Answer 3

Gives mass of sample molecules, plus information about bonding from fragments

Pros: Gives molecular formula, good for mixture analysis, tiny sample needed
Cons: Difficult to interpret when unknown

Question 4

Electrospray ionisation steps

Answer 4

• Solution of sample sprayed through high potential nozzle
• Solvent evaporates leaving charged droplets
• Target molecule with ion attached is detected

Question 5

IR Spectroscopy

Answer 5

Detects vibrational transitions in bonds. Only works when vibration leads to change in dipole moment.

Question 6

Wavenumber equation

Answer 6

Question 7

Raman spectroscopy

Answer 7

Used when there is no change in dipole moment