Aspirin


Aspirin

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Figure 1.1: H NMR spectra for aspirin

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Figure 1.2: A peak at 2.2987 ppm, which corresponds to the three equivalent H protons on the methyl group attached to the carbonyl on the left side of the ester in the aspirin molecule. These protons are expected to measure at 2.1 ppm. While 2.2987 ppm is relatively close to this expected location, these protons are more deshielded, causing a slightly higher reading.

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Figure 1.3: A small broad peak at 5.023 ppm, which corresponds to the carboxylic acid in the molecule. NMR for carboxylic acids is variable, which explains why we see this broad peak at 5 ppm, instead of 10-12 ppm.

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Figure 1.4: A zoomed view of the sets of doublets and triplets present in the NMR spectra. The doublets appear at approximately 8.050 ppm and 7.150 ppm, while the triplets appear at approximately 7.620 ppm and 7.360 ppm. The positioning of these peaks is consistent with the aromatic ring present in the aspirin molecule, and coupling of adjacent protons accounts for the signal splitting into doublet and triplet groups.[Is that what you would expect from what we learned in class? JCB]

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Figure 1.5: An IR spectra for aspirin.

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Figure 1.6: The useful region of the aspirin IR spectra.

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Figure 1.7: The first portion of the useful region of aspirin IR. As expected, there is a spike at 1605 cm-1 corresponding with the benzene ring. Also, there are spikes present at 1680 and 1750 cm-1, which correspond to the 2 carbonyls present in the molecule, even though they are slightly shifted from the expected 1730-1740 cm-1 range. The peak at 1680 cm-1 is shifted to a lower wavenumber than the expected range due to conjugation with C=C in the attached benzene ring.

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Figure 1.8: The second portion of the useful region of aspirin IR. These spikes are wider and shorter than those in Figure 1.7. This broadness is expected, between 2500 and 3500 ppm, due to the presence of the carboxylic acid in the aspirin molecule.

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