4.2.4 Analytical techniques

Question 1

what happens to an organic compound when placed in a mass spectrometer

Answer 1

• loses an electron + forms a positive ion, the molecular ion
• mass spectrometer detects mass-to-charge ratio of molecular ions which gives molecular mass of compound

Question 2

how can you find the molecular mass from a mass spectrum

Answer 2

• the molecular ion peak (M+ peak) has to be located
  > its the clear peak at the highest m/z value on the right-hand side of the mass spec

Question 3

what is infrared

Answer 3

• heat energy

Question 4

what happens to a covalent bond when you fire infrared radiation at it

Answer 4

• bond absorbs the IR, making them bend + stretch
  > each bond vibrates as it absorbs the IR

Question 5

bonds vibrating from IR can depend on some factor such as:

Answer 5

• bond strength (stronger=faster)
• bond length (shorter=faster)
• mass of each atom involved in bond (heavy atoms=slower)

Question 6

in an IR spectrum, what does the height of the peak represent

Answer 6

• the amount of energy absorbed due to bond stretching
• lower peak / transmittance = more energy absorbed
• lower transmittance = higher absorption

Question 7

what are wavenumbers above 1500cm-1 used to identify

Answer 7

• functional groups

Question 8

what are wavenumber below 1500cm-1 used to identify

Answer 8

• used for fingerprinting

Question 9

how can you differentiate between a C-H and an O-H bond in an IR spec

Answer 9

• peak for OH is more broad

Question 10

what is elemental analysis

Answer 10

• use of percentage composition data to determine empirical formula