Infra-Red and Mass Spectroscopy Webquest Modern Analytical Techniques

Propanone

Propanal

Propanoic Acid

Propan–1–ol

Propanone - C 3 H 6 O M r = 58 I have identified the mass spectrum for Propanone, as the mass spectrum below. Firstly this is because the relative formula mass for propanone is 58, and this corresponds with the Molecular ion peak (M+) having an m/z of 58 on the mass spectrum below. The base peak is at m/z = 43, which means that the most common fragment ion formed has a relative formula mass of 43. It appears that what causes the base peak at m/z = 43, is the fragment CH 3 CO +, which is produced by the following fragmentation: C 3 H 6 O CH 3 CO + + CH 3. (only possible in Propanone) M+ CH 3 CO + Cont. on next slide CH 3 +

M+ CH 3 CO + CH 3 + This is the infra-red spectroscopy that I have chosen for Propanone. Firstly because there is a peak between cm -1, this suggests that the molecule has a C=O, but there is no broad peaks between cm -1 or cm -1 which suggests that this is not an alcohol or carboxylic acid, respectively, but is a ketone. There is also a smaller peak at m/z 15, which is caused by another fragment ion, which in this case is CH 3 +, caused by this fragmentation: C 3 H 6 O CH CH 3 CO. (possible in all molecules in this investigation) C=O

Propanal - C 3 H 6 O M r = 58 I have identified the mass spectrum for Propanal, as the mass spectrum below. Firstly this is because the relative formula mass for Propanal is 58, and this corresponds with the Molecular ion peak (M+) having an m/z of 58 on the mass spectrum below. This is also the base peak, as it is the tallest line in the spectrum, and so it is the most common ion formed. Fragment ions are also formed, the peak at m/z = 29 suggests two possible fragment ions: C 2 H 5 + and CHO +, both of these fragment ions contribute towards the peak at m/z = 29 M+ Cont. on next slide C 2 H 5 +, CHO + C3H5O+C3H5O+

M+ The C 2 H 5 + and CHO + fragment ions are produced by the following fragmentations: C 3 H 6 O C 2 H CHO. (possible in propanal, propanoic acid, and propan-1-ol) C 3 H 6 O CHO+ + C 2 H 5. (possible in propanal, propanoic acid, and propan-1-ol) These two fragment ions are what distinguish this mass spectrum from that of Propanone, both have the same M r of 58 and so it can be hard to distinguish the two different molecules, but through the production of fragment ions, we can tell that this mass spectrum belongs to propanal, as you cannot get fragments of C 2 H 5 + or CHO+ from propanone, just as for the mass spectrum of Propanone, you get a CH 3 CO+ fragment ion, which you cannot produce from Propanal. Cont. on next slide C3H5O+C3H5O+

C 2 H 5 +, CHO + M+ Another fragment ion produced is C 3 H 5 O + which produces the peak at m/z = 57, which is formed by the following fragmentation: C 3 H 6 O C 3 H 5 O + + H. C3H5O+C3H5O+ This is the infra-red spectroscopy that I have chosen for Propanal. Firstly because there is a peak between cm -1, this suggests that the molecule has a C=O, but there is no broad peaks between cm -1 or cm -1 which suggests that this is not an alcohol or carboxylic acid, respectively. The absorbtions between cm -1 are characteristic of an aldehyde, and are what distinguishes this IR spectrum from that of propanone, wich does not have these absorbtions. (possible in propanal, propanoic acid, and propan-1-o l) C=O

Propanoic Acid - C 2 H 5 COOH M r = 74 I have identified the mass spectrum for Propanoic Acid, as the mass spectrum below. Firstly this is because the relative formula mass for Propanoic Acid is 74, and this corresponds with the Molecular ion peak (M+) having an m/z of 74 on the mass spectrum below. This is also the base peak, as it is the tallest line in the spectrum, and so it is the most common ion formed. Fragment ions are also formed, the peak at m/z = 73 suggests that the fragment ion causing the peak is C 2 H 5 COO +, which is caused by the following fragmentation: M+ C 2 H 5 COO + COOH + CO + C2H5+C2H5+ Cont. on next slide

M+ C 2 H 5 COO + COOH + CO + C2H5+C2H5+ C 2 H 5 COOH C 2 H 5 COO + + H. (only possible in propanoic acid) The peak at m/z = 45 suggests the fragment ion formed is COOH+: C 2 H 5 COOH COOH+ + C 2 H 5. (only possible in propanoic acid) The peak at m/z = 29 suggests the fragment ion formed is C 2 H 5 +: C 2 H 5 COOH C 2 H COOH. (possible in propanal, propanoic acid, and propan-1-ol) The peak at m/z = 28 suggests the fragment ion formed is CO+: C 2 H 5 COOH CO+ + C 2 H 5. + OH. (possible in all molecules in this investigation) Cont. on next slide

This is the infra-red spectroscopy that I have chosen for Propanoic Acid. Firstly because there is a peak between cm -1, this suggests that the molecule has a C=O bond, and there is a very broad peak between cm -1, which suggests that the molecule has an O-H bond, characteristic of a carboxylic acid, there is also a peak between cm -1, which suggests that the molecule has a C-O bond. The IR spectroscopy shows all of these bonds and therefore out of the four molecules, the IR spectrum must be that of Propanoic acid as none of the other molecules contain all three types of bond present in this spectrum. C=O O-H C-O

Propan-1-ol - C 3 H 7 OH M r = 60 I have identified the mass spectrum for Propan-1-ol, as the mass spectrum below. Firstly this is because the relative formula mass for propan-1-ol is 60, and this corresponds with the Molecular ion peak (M+) having an m/z of 60 on the mass spectrum below. The base peak is at m/z = 31, which means that the most common fragment ion formed has a relative formula mass of 31. It appears that what causes the base peak at m/z = 31, is the fragment CH 2 OH +, which is produced by the following fragmentation: CH 2 OH + M+ C2H5+C2H5+ C3H6+C3H6+ Cont. on next slide

CH 2 OH + M+ C2H5+C2H5+ C3H6+C3H6+ C 3 H 7 OH CH 2 OH + + C 2 H 5. (only possible in propan-1-ol) The peak at m/z = 29 suggests the fragment ion formed is C 2 H 5 + : C 3 H 7 OH C 2 H CH 2 OH. (possible in propanal, propanoic acid, and propan-1-ol) The peak at m/z = 42 suggests the fragment ion formed is C 3 H 6 + : C 3 H 7 OH C 3 H OH. + H. (possible in propanone, propanal and propan-1-ol) Cont. on next slide

This is the infra-red spectroscopy that I have chosen for Propan-1-ol. Firstly because there is a broad peak between cm -1, which suggests that the molecule has an O-H bond which is characteristic of an alcohol, the IR spectrum also has a peak between cm -1, suggesting the molecule has a C-O bond. What also distinguishes this IR spectrum from the ones for the other molecules, is that this one does not have a peak between cm -1, which denotes a C=O bond, which an alcohol does not contain and therefore out of the options, this must be the IR spectrum for Propan-1-ol. O-H C-O