1. What do you remember about mass spectrometry?

2. The mass spectrometer can give information about the relative isotopic abundances of different elements

3. Antimony has two isotopes 121-Sb and 123-Sb
Antimony has two isotopes 121-Sb and 123-Sb. In a bullet at a crime scene there was a sample of antimony containing 57.3% 121-Sb and 42.7% 123-Sb. Calculate the relative atomic mass of the sample of antimony from the bullet.

4. This type of data may also be presented in graphical form from a mass spectrometer.

5. Tungsten 4 3
Relative abundance 2 1
182
183
184
185
186
M/Z

6. Chlorine Relative abundance Relative atomic mass 4 3 2 1 34 35 36 3738
Relative atomic mass

7. Identifying organic compounds
Organic molecules do not hold charge well.
The ions break up or fragment.
They break into smaller ions and neutral fragments.
They do this in regular patterns.
i.e. the same molecule always fragments in the same way.
This allows us to analyse them.

8. Mass spectrum of propan-1-ol

9. Mass Spectrum of ethanol
Molecular ion: tells you the molecular mass of the whole compound.

10. Mass Spectrum of ethanol: Identify the fragments responsible for the following peaks:46 45 31 29 15

11. Possible fragments + + 45 31 M+ + 46 + + + + 29 15

12. Identify the fragments responsible for the peaks at 15, 29 and 44 and thus identify this alkane.
Propane

13. Mass Spectrum of an alcohol
Mass Spectrum of an alcohol. Identify the alcohol and draw structures for the fragment ions represented by the peaks at: 60, 59, 43, 31 and 29.

14. Possible fragments + + 59 31 M+ + 60 + + + + 43 29

15. IR spectroscopy All molecules absorb Infra-red radiation
The absorbed energy makes covalent bonds vibrate (bending or stretching)

16. INFRA RED SPECTROSCOPY
Molecules can absorb Infra-red radiation
The absorbed energy makes covalent bonds vibrate

17. Symmetrical
stretching
Antisymmetrical
stretching
Scissoring
Rocking
Wagging
Twisting

18. e.g. H2O – only the stretching (top row) involve a change in dipole
For a molecule to absorb IR photons there must be a CHANGE IN DIPOLE in the bond stretch or vibration
e.g. H2O – only the stretching (top row) involve a change in dipole
Symmetrical
stretching
Antisymmetrical
stretching
Scissoring
Wagging
Twisting
Rocking

19. Molecules such as O2 and N2 do not appear on an IR spectrum.
Symmetrical
stretching
Antisymmetrical
stretching
Scissoring
Wagging
Twisting
Rocking

20. INFRA RED SPECTROSCOPY
Each bond vibrates and therefore absorbs infra-red radiation.
The exact frequency depends on:
The bond strength
The bond length
The mass of each atom in the bond

21. The Infra-red Spectrophotometer
• a beam of infra red radiation is passed through the sample
• a similar beam is passed through the reference cell
• the frequency of radiation is varied
• bonds vibrating with a similar frequency absorb the radiation
• the amount of radiation absorbed by the sample is compared with the reference
• the results are collected, stored and plotted

22. The Infra-red Spectrophotometer
A bond will absorb radiation of a frequency similar to its vibration(s)
normal vibration
vibration having absorbed energy

23. The spectrum
Vertical axis Absorbance the stronger the absorbance the larger the peak
Horizontal axis Frequency wavenumber (waves per centimetre) / cm-1

24. INFRA RED SPECTRA - USES
IDENTIFICATION OF PARTICULAR BONDS
IN A MOLECULE
The presence of bonds such as O-H and C=O within a molecule can be confirmed because they have characteristic peaks in identifiable parts of the spectrum.

25. IDENTIFICATION OF COMPOUNDS BY DIRECT COMPARISON OF SPECTRA
INFRA RED SPECTRA - USES
IDENTIFICATION OF PARTICULAR BONDS
IN A MOLECULE
The presence of bonds such as O-H and C=O within a molecule can be confirmed because they have characteristic peaks in identifiable parts of the spectrum.
IDENTIFICATION OF COMPOUNDS BY DIRECT COMPARISON OF SPECTRA
The only way to completely identify a compound using IR is to compare its spectrum with a known sample. The part of the spectrum known as the ‘Fingerprint Region’ is unique to each compound.

26. Uses of IR spectroscopy - Forensic science - Breathalyzers - Quality control in perfume production - Drug analysis

27. FINGERPRINT REGION
• organic molecules have a lot of C-C and C-H bonds within their structure
• spectra obtained will have peaks in the 1400 cm-1 to 800 cm-1 range
• this is referred to as the “fingerprint” region
• the pattern obtained is characteristic of a particular compound the frequency
of any absorption is also affected by adjoining atoms or groups.

28. Interpreting spectra You must be able to identify the following peaks.
You will have a data sheet to help.
C-O in alcohols, esters & carboxylic acids
C=O in aldehydes, ketones and carboxylic acids
C-H in alkanes/alkenes/aldehydes
O-H in carboxylic acids
(very broad)
O-H in alcohols
(broad)

29. IR SPECTRUM OF A CARBONYL COMPOUND
• carbonyl compounds show a sharp, strong absorption between 1700 and 1760 cm-1
• this is due to the presence of the C=O bond

30. IR SPECTRUM OF AN ALCOHOL
• alcohols show a broad absorption between 3200 and 3600 cm-1
• this is due to the presence of the O-H bond

31. IR SPECTRUM OF A CARBOXYLIC ACID
• carboxylic acids show a broad absorption between 3200 and 3600 cm-1
• this is due to the presence of the O-H bond
• they also show a strong absorption around 1700 cm-1
• this is due to the presence of the C=O bond

32. IR SPECTRUM OF AN ESTER
• esters show a strong absorption between 1750 cm-1 and 1730 cm-1
• this is due to the presence of the C=O bond

33. WHAT IS IT?
One can tell the difference between alcohols, aldehydes and carboxylic acids by comparison of their spectra.
ALCOHOL
O-H STRETCH
ALDEHYDE
C=O STRETCH
O-H STRETCH
C=O STRETCH
AND
CARBOXYLIC ACID

34. Identify the group next to the yellow box using the key below.
C-O in alcohols, esters & carboxylic acids
C=O in aldehydes, ketones and carboxylic acids
C-H in alkanes/alkenes/aldehydes
O-H in carboxylic acids
(very broad)
O-H in alcohols
(broad)

35. Identify the groups next to the yellow boxes using the key below.
C-O in alcohols, esters & carboxylic acids
C=O in aldehydes, ketones and carboxylic acids
C-H in alkanes/alkenes/aldehydes
O-H in carboxylic acids
(very broad)
O-H in alcohols
(broad)

36. C-O in alcohols, esters & carboxylic acids
C=O in aldehydes, ketones and carboxylic acids
C-H in alkanes/alkenes/aldehydes
O-H in carboxylic acids
(very broad)
O-H in alcohols
(broad)

37. Working backwards Which peaks would be present in the spectrum of…
Working backwards Which peaks would be present in the spectrum of….? a) A ketone b) A secondary alcohol c) Alkene

38. Exam question A compound was analysed by IR spectroscopy and Mass spectrometry. It gave strong absorbance at 1740 cm-1 and peaks at m/z values of 15, 29 and 72. The compound had the following composition by mass: C, 66.63%; H, 11.18%; O, 22.19%. Use this information to identify two possible structures of this compound.

39. Exam question A compound was analysed by IR spectroscopy and Mass spectrometry. It gave strong absorbance at 1740 cm-1 and peaks at m/z values of 15, 29 and 72. The compound had the following composition by mass: C, 66.63%; H, 11.18%; O, 22.19%. Use this information to identify two possible structures of this compound. 1) Calculate the empirical formula 2) Use IR spectrum to identify the functional group(s) 3) Use Mass spectrum to identify the parent ion (and therefore the molecular formula) 4) Use Mass spectrum to identify the fragments 5) Suggest the two possible identities of the molecule

40. Exam question A compound was analysed by IR spectroscopy and Mass spectrometry. It gave strong absorbance at 1740 cm-1 and peaks at m/z values of 15, 29 and 72. The compound had the following composition by mass: C, 66.63%; H, 11.18%; O, 22.19%. Use this information to identify two possible structures of this compound. 1) Calculate the empirical formula: C4H8O 2) Use IR spectrum to identify the functional group(s) : C=O 3) Use Mass spectrum to identify the parent ion (and therefore the molecular formula) 72, so C4H10O 4) Use Mass spectrum to identify the fragments : 15 = CH = C2H5+ 5) Suggest the two possible identities of the molecule: Butanal or butanone

41. Watch the video clip and answer the questions
How can a pair of atoms joined by a covalent bond be described?
What frequency is needed to increase the vibration of molecules?
How can we identify different functional groups?
Why is a blank needed?
How can an unknown sample be identified?

42. Whiteboard quiz

43. Quiz 1) Identify the species responsible for the peak at m/z = 29

44. 2) Structural formula of 1-chlorobutane

45. 3) What is the mass of the molecular ion?

46. 4) Skeletal formula of ethanol

47. 5) How do you get from an alcohol to a carboxylic acid?

48. 6) What is missing?

49. 7) Identify the group next to the yellow box.
C-O in alcohols, esters & carboxylic acids
C=O in aldehydes and ketones
C-H in alkanes/alkenes/aldehydes
O-H in carboxylic acids
(very broad)
O-H in alcohols/carboxylic acids
(broad)

50. 8) Draw the mechanism for the reaction of ethene with Hydrogen Bromide