How do you rationalize an infrared spectrum of salicylic acid and aspirin? How do you know which is which?
To rationalize an infrared (IR) spectrum of salicylic acid and aspirin, you can compare the spectral patterns and functional groups present in each compound.
1. Familiarize yourself with the IR spectrum: Infrared spectroscopy measures the absorption of infrared light by chemical bonds. Different functional groups absorb infrared radiation at characteristic frequencies, resulting in peaks in the IR spectrum.
2. Study the functional groups: Salicylic acid and aspirin have distinct functional groups that can be identified in their IR spectra. Salicylic acid contains a hydroxyl (-OH) group and a carboxylic acid (-COOH) group. Aspirin, on the other hand, has an ester (-COO-) group.
3. Analyze the spectra: Compare the IR spectra of salicylic acid and aspirin to identify specific peaks associated with their respective functional groups.
- Salicylic Acid: In the IR spectrum of salicylic acid, you will observe a broad peak around 3200-3500 cm-1, corresponding to the O-H stretching vibration of the hydroxyl group. Additionally, there will be a strong peak around 1700-1750 cm-1, representing the C=O stretching vibration of the carboxylic acid group.
- Aspirin: In the IR spectrum of aspirin, you will see a peak around 1750-1755 cm-1, which corresponds to the C=O stretching vibration of the ester group (-COO-).
4. Differentiate between the spectra: By analyzing the peaks associated with the functional groups, you can distinguish between salicylic acid and aspirin. The presence of the -OH peak in the range of 3200-3500 cm-1 is indicative of salicylic acid, while the presence of the ester C=O peak around 1750-1755 cm-1 indicates aspirin.
By comparing the respective peaks in the IR spectra, you can determine whether the sample is salicylic acid or aspirin. Keep in mind that the overall interpretation of an IR spectrum involves considering other peaks and patterns as well, but the key functional group peaks mentioned above are the most indicative for differentiating between salicylic acid and aspirin.