Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: pallidol on August 06, 2017, 02:55:43 AM
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Hi there. I need some suggestion in my labwork.
I performed dieckmann cyclisation reaction using Na/MeOH and reflux for two hours. Then MeOH was dried up and water was added followed by acidification until pH 1-2. But no precipitate was obtained the I took the aqueous and washed it using ethyl acetate. The organic layer was dried using Na2SO4 and dried under vacuum. The NMR showed no product of interested.
So i redo the reaction and modified the work-up procedure a little bit. After two hours reaction MeOH was dried up and I added drop wise 1M of HCl, followed by drop wise of NaHCO3. Then i took the aqueous and bring it under vacuum to give slightly brownish solid.
From NMR analysis, i have figured out the expected structure might compatible to the spectrum eventhough there is a cleavages . But one peak is missing. I am not sure whether Dieckmann cyclisation really took part in my reaction. Here i attach the NMR spectra (1H, APT, HMBC, HMQC) for the reference.
Thank you beforehand.
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1). If Bn = benzyl; benzyl ether cleavage is not possible under the described reaction and further treatment conditions.
2). In general; protons intgeration precision decreases, as the number of protons increases.
3). Taking an IR spectrum, will help the structure identification because the deprotected alcohol will form intermolecular H-bonding that appears further than 3500 cm-1. Besides, if the carboxylate ester is partially hydrolyzed, carboxylic acids have a characteristic IR appearance at that zone, too.