Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: AllylicAzideUMN on March 10, 2018, 03:08:50 PM
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My research involves perylene derivatives that are notoriously insoluble in common organic solvents. One of the most frustrating aspects of my work is obtaining useful NMR, IR, GC-MS, and TLC data on my compounds that will barely go into solution. Using DMSO as the solvent for my NMR and GC samples, I often obtain spectra whose peaks are so low intensity that they are buried in noise. I encounter similar issues with TLC. IR often works using a thin layer of solid compound on a NaCl plate, but my absorption values are usually very low and noisy. Therefore, I have a difficult time interpreting how well my chemistry is going. I have tried alternative solvents such as pyridine, but pyridine has NMR signals that overlap with my compound's and isn't much better at solubilizing my compounds. What other analytical techniques or tricks may allow me to better analyze my insoluble compounds?
Thank you in advance for the advice! I appreciate it very much.
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Use other solvents? I mean, you can run NMR in vide variety of solvents, not only DMSO or CDCl3. There is methanol, acetic acid, benzene, water, DMF... What solvent are you using for your reactions?
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Thank you for your response.
I have been attempting my reactions with the most insoluble compounds in methanol, ethanol, or chlorobenzene. However, these solvents do not dissolve my compounds even at elevated temperatures (120 degrees with chlorobenzene). I don't think there is a solvent that will beat DMSO. I haven't tried acetic acid yet, so that is something I can look into.
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For FTIR - have you tried it in ATR mode?
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have you tried increasing the number of scans the NMR machine records, any noise should be cancelled out by repeated scans.
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I'm sure it's totally compound-dependent, but d5-pyridine has dissolved several compounds of mine that nothing else would touch, even DMSO...
Apologies for skim-reading the first time - just read your (very clear) discussion of your attempts at using pyridine as a solvent...
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For FTIR - have you tried it in ATR mode?
Yes a pure powder in an ATR setup should give beautiful spectra. Most undergrad labs have one.
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CRC Handbook of Chem & Phys. gives VERY soluble in acetone for Perilene.
Otherwise, do a lit. search for synthesis of Perilene compounds similar to yours; this will indicate solvents used.
Please let us know what works!
Regards.
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Also consider decalin, which dissolves resins and fuel additives (Wiki).
Based on the premise that like dissolves like.
I know, I know..
Regards