organic synthesis and analytical techniques

Question 1

effect of infrared radiation on covalent bonds

Answer 1

makes covalent bonds vibrate more when radiation is absorbed

Question 2

how to identify functional groups using IR spectrum

Answer 2

use wavenumber and compare with datasheet

Question 3

uses of IR spectroscopy

Answer 3

modern breathalysers
monitoring gases causing air pollution

Question 4

how to determine Mr of a molecule using mass spectrometry

Answer 4

the M+ peak (furthest right) gives an m/z value equal to the Mr of the compound

Question 5

what causes the small M+1 peak

Answer 5

presence of the C-13 isotope

Question 6

what does fragmentation of a molecule produce?

Answer 6

a positive +1 fragment ion and a neutral species
eg CH3CH2OH can be fragmented into CH3CH2 and +OH

Question 7

uses of mass spectrometry

Answer 7

detecting drugs
analysing molecules in space

Question 8

method for purifying organic liquids

Answer 8

1 - heat under reflux/distillation
2 - separate aqueous and organic layer using a separating funnel
3 - remove acid impurities using NaHCO3
4 - dry using anhydrous salt eg MgSO4
5 - redistill at the compound’s boiling point

Question 9

method for purifying organic solids

Answer 9

1 - heat under reflux/distillation
2 - cool and filter under reduced pressure
3 - recrystallisation
- dissolve in a minimum volume of hot solvent
- cool and filter solid
- wash with cold water
- dry
4 - test purity

Question 10

how to test purity of an organic solid

Answer 10

determine melting point
compare with known data
pure compounds will have a sharp melting point range