17) SPECTROSCOPY

Question 1

what can a mass spectrometer be used for?

Answer 1

-identify unknown compound
-find relative abundance of each isotope
-determine structural info

Question 2

how is the Mr of a compound determined from a mass spectrum?

Answer 2

1) organic compound placed into mass spectrometer
2) vaporized
3) bombarded with e-
4) loses an e-
5) forms a +ve ion = MOLECULAR ION (M+)
6) process is called IONISATION

Question 3

what is the ionisation equation ?

Answer 3

neutral compound –> [molecular ion]+ + e-

Question 4

what happens when the molecular ion reaches the detector?

Answer 4

the mass-to-charge (m/z) ration of the molecular ion is detected

Question 5

what is the equation to finding the Mr of the compound?

Answer 5

m/z ratio of molecular ion = Mr of compound

Question 6

how can you find the relative molecular mass using the mas spectrum?

Answer 6

-locate molecular ion peak
-clear peak
-highest m/z value on the mass spectrum = furthest to the right

Question 7

what is the M+1 peak?

Answer 7

-very small peak 1 unit after the M+ peak
-result of isotopes

Question 8

what is fragmentation?

Answer 8

when the molecular ion breaks up into smaller pieces called fragments

Question 9

what is the cause of fragmentation?

Answer 9

-breaking of covalent ions in the molecular ion
-fragment ion is formed + can be detected + appears in mass spectrum

Question 10

what else is formed due to fragmentation?

Answer 10

-neutral or radical species –> not detected in mass spectrum