Dear blog reader , this post is for brushing up our fundamentals of spectroscopy using simple molecules like aspirin
text may be less but graphs are educative. one can browse through this to brush up
Product Name: Acetylsalicylic acid CAS:50-78-2
1H NMR
Assign. Shift(ppm)
A 11.
B 8.125
C 7.624
D 7.356
E 7.142
F 2.352
ABOVE IS PROTON NMR OF ASPIRIN AND ITS INTERPRETATION
abelled.The peaks I have are:
- 2.30ppm (I this is a singlet and would be F)
- 7.07ppm (I think this is E)
- 7.29ppm (I think this is D)
- 7.53ppm (I think this is C)
- 8.05ppm (I think this is B)
- 11.44ppm (this is a singlet and would be A)
For B,C,D,E I need to say what kind of splitting pattern there would be and how many coupling constants are present and there approximate value. I think I know the assignments of them but I don't know the splitting pattern or coupling constants.
Would E and B be doublet of doublets because they couple with D and C so they would have ortho and meta coupling?
Would D and C be coupling with each other and B and E so would they be doublet of doublets of doublets, with two ortho and one meta coupling?
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BELOW IS IR OF ASPIRIN KBR DISC
IR in nujol mull
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MASS SPECTRUM
above is mass spectrum of aspirin
o-acetoxybenzoic acid C9H8O4 (Mass of molecular ion: 180)
Source Temperature: 170 °C Sample Temperature: 100 °C DIRECT, 75 eV
13 C NMR
above is 13 C NMR OF ASPIRIN
| 50.18 MHz | |
| C9 H8 O4 | 0.039 g : 0.5 ml CDCl3 |
ppm Int. Assign.
170.20 450 1
169.76 510 2
151.28 560 3
134.90 924 4
132.51 1000 5
126.17 986 6
124.01 974 7
122.26 397 8
20.99 674 9
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below is Raman spectra of aspirin
NMR INTERPRETATIONS
H-NMR spectral analysis
 CAS NO. 50-78-2, Acetylsalicylic acid H-NMR spectral analysis |
C-NMR spectral analysis
 CAS NO. 50-78-2, Acetylsalicylic acid C-NMR spectral analysis H, H-COSY spectrum
In H, H-COSY spectrum are on both axes, the 1 H chemical shifts plotted; In principle, both the axes 1 to see H-NMR spectra. Thus, there is a symmetric to the diagonal diagram.
1 H-NMR spectrum of acetylsalicylic acid
H, H-COSY spectrum of acetylsalicylic acid
In the spectrum, only the range from 7.0 to 8.2 ppm is applied, because only here HH scalar couplings can be expected.
There are two types of signals:
In general it can be seen in the COSY spectrum each scalar coupling between two nuclei at four signals (two cross and two diagonal peaks) resulting connected a square; in the following example, the vicinal coupling between the H atoms is highlighted 3 and 4.
With good resolution of the COSY spectrum, the coupling constants can be determined from the fine structure of the cross and diagonal signals, but this is rarely done because of the 1-D H-NMR spectra is easily possible.
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