1. R W Grime Ripon Grammar School
18/06/2018
MASS SPECTROSCOPY
R W Grime Ripon Grammar School

3. HIGH RESOLUTION MASS SPECTROSCOPY
Molecular ion formed: M → [M]+. + e–
m/z value for [M]+. gives the Mr.
High resolution measures m/z to enough accuracy to find the molecular formula.
e.g. Mr = 60
CH3COOH molecular formula = C2H4O2
NH2CONH molecular formula = CH4N2O
CH3CH2CH2OH molecular formula = C3H8O
CH3CH(OH)CH molecular formula = C3H8O

4. FRAGMENTATION
Molecular ion fragments due to covalent bonds breaking: [M]+. → X+ + Y.
Much information from fragmentation patterns – can often work out structure.
Relatively stable ions such as carbocations R+ and acylium ions [R-C=O]+ are common.
The more stable the ion, the greater the peak intensity.
m/z 15 29 31 43 57
fragment
CH3+
CH3CH2+
CH2OH+
CH3CH2CH2+
(CH3)2CH+
CH3CO+
CH3CH2CO+

5. butane CH3CH2CH2CH3 C4H10  [C4H10]+. + e–
m/z 58
[C4H10]+.  [CH3CH2CH2]+ + .CH3
m/z 43
[CH3CH2CH2]+
[C4H10]+.  [CH3CH2]+ + .CH2CH3
m/z 29
[CH3CH2]+
[C4H10]+.

6. ISOTOPES Ions with different isotopes produce different signals.
Most important for Br and Cl.
Br: 50% 79Br % 81Br
Cl: 75% 35Cl % 37Cl
If two or more Br/Cl atoms, then spectrum is more complicated.
Often small peaks at m/z + 1 due to 2H and 13C.

7. bromomethane CH3Br CH381Br  [CH381Br]+. + e–
m/z 96
CH379Br  [CH379Br] e–
m/z 94
[CH3Br]+.  [CH3]+ + .Br
m/z 15
[CH3]+
[CH379Br]+.
[CH381Br]+.

8. chloroethane CH3CH2Cl CH3CH237Cl  [CH3CH237Cl]+. + e–
m/z 66
CH3CH235Cl  [CH3CH235Cl] e–
m/z 64
[CH3CH237Cl]+.  [CH237Cl]+ + .CH3
m/z 51
[CH3CH2]+
[CH3CH235Cl]+.  [CH235Cl]+ + .CH3
m/z 49
[CH3CH235Cl]+.
[CH3CH2Cl]+.  [CH3CH2]+ + .Cl
m/z 29
[CH237Cl]+
[CH235Cl]+
[CH3CH237Cl]+.

9. dichloromethane CH2Cl2 37Cl : 35Cl = 1 : 3
37Cl2 : 35Cl37Cl : 35Cl2 = 1 : 6 : 9
[CH235Cl]+
[CH235Cl2]+.
[CH237Cl35Cl]+.
[CH237Cl]+
[CH237Cl2]+.

10. dibromomethane CH2Br2 81Br : 79Br = 1 : 1
81Br2 : 81Cl79Br : 79Br2 = 1 : 2 : 1
174 [CH281Br79Br]+.
93 [CH279Br]+
95 [CH281Br]+
172 [CH279Br2]+.
176 [CH281Br2]+.

11. butanone CH3CH2COCH3 CH3CH2COCH3  [CH3CH2COCH3]+. + e–
m/z 72
[CH3CH2COCH3]+.  [CH3CH2CO]+ + .CH3
m/z 57
[CH3CH2COCH3]+.  [CH3CO]+ + .CH2CH3
m/z 43
[CH3CO]+
[CH3CH2COCH3]+.  [CH3CH2]+ + .COCH3
m/z 29
[CH3CH2]+
[COCH2CH3]+
[CH3COCH2CH3]+.

12. methyl butanoate CH3CH2CH2COOCH3
CH3CH2CH2COOCH3  [CH3CH2CH2COOCH3]+. + e–
m/z 102
methyl butanoate
CH3CH2CH2COOCH3
[CH3CH2CH2COOCH3]+.  [CH3CH2CH2COO]+ + .CH3
m/z 87
[CH3CH2CH2COOCH3]+.  [CH3CH2CH2CO]+ + .OCH3
m/z 71
[CH3CH2CH2COOCH3]+.  [COOCH3]+ + .CH2CH2CH3
m/z 59
[CH3CH2CH2]+
[CH3CH2CH2COOCH3]+.  [CH3CH2CH2]+ + .COOCH3
m/z 43
[CH3CH2CH2COOCH3]+.  [CH3CH2]+ + .CH2COOCH3
m/z 29
[CH3CH2CH2CO]+
[COOCH3]+.
[CH3CH2CH2COO]+
[CH3CH2]+
[CH3CH2CH2COOCH3]+.

13. propyl methanoate
methylethyl methanoate
ethyl ethanoate
methyl propanoate

14. propyl methanoate [OCH2CH2CH3]+ m/z 59 [HCO]+ m/z 29 [CH2CH2CH3]+
[HCOO]+
m/z 45

15. methylethyl methanoate
[OCH2(CH3)2]+
m/z 59
[HCO]+
m/z 29
[CH2(CH3)2]+
m/z 43
[HCOO]+
m/z 45

16. ethyl ethanoate [OCH2CH3]+ m/z 45 [CH3CO ]+ m/z 43 [CH2CH3]+ m/z 29
[CH3COO ]+
m/z 59

17. methyl propanoate [OCH3]+ m/z 31 [CH3CH2CO ]+ m/z 57 [CH2CH3]+ m/z 29
[CH3OCO ]+
m/z 59