Fragmentation

Question 1

The molecular ion peak can be used to identify the

Answer 1

molecular mass of a compound

Question 2

However, different compounds may have the same molecular mass
To further determine the structure of the unknown compound, …………………is used

Answer 2

fragmentation

Question 3

Fragments may appear due to the formation of

or loss of

Answer 3

characteristic fragments or the loss of small molecules

Question 4

Fragments may appear due to the formation of characteristic fragments or the loss of small molecules

For example, a peak at 29 is due to the characteristic fragment C2H5+­­
Loss of small molecules give rise to peaks at 18 (H2O), 28 (CO), and 44 (CO2)

Question 5

Simple alkanes are fragmented in mass spectroscopy by breaking the

Answer 5

c-c bonds

Question 6

Halogenoalkanes
Halogenoalkanes often have multiple peaks around the molecular ion peak
This is caused by the fact that

Answer 6

there are different isotopes of the halogens

Question 7

Alcohols often tend to lose a water molecule giving rise to a peak at

Answer 7

18 below the molecular ion

Question 9

Another common peak is found at m/e value 31 which corresponds to the CH2OH+­­ fragment
For example, the mass spectrum of propan-1-ol shows that the compound has fragmented in four different ways:

Answer 9

Loss of H* to form a C3H7O+ fragment with m/e = 59

Loss of a water molecule to form a C3H6+ fragment with m/e = 42

Loss of a *C2H5 to form a CH2OH+ fragment with m/e = 31
And the loss of *CH2OH to form a C2H5+ fragment with m/e = 29