Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: Bertha12 on April 28, 2016, 08:35:06 AM
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Hi everyone! I was wondering if I could get some help. I'm supposed to be able to figure out the name of the this compound. I know for a fact that it is some sort of Carboxylic acid, but I can't seem to figure out a name for it. Thank you in advance!
By the way, it has a melting point of 105-110. Also, in case I didn't make it clear, this is for Organic Chemistry.
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Welcome to the forum. It is a forum rule that you must show your attempt to answer your question before we can help you. A good place to start might be the H-1 NMR spectrum. What information can you find there?
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Oh my apologies, I didn't know that. Well, I believe that a signal at 7.5ish indicates some sort of aromaticity, right? I asked my teacher about the lack of a signal at 3-4 (for the carboxylic -H), and he said sometimes the H MNRs don't show it. I just find it extremely confusing, because any of the aromatic carboxylic acids I've looked up (benzoic acid, gallic acid, etc), do not match neither my IR scan nor my H MNR.
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I am tempted to question whether or not the IR spectrum is for the same compound.
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What makes you think that?
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Suppose that the H-1 NMR is of benzoic acid. What would you expect the IR to look like (what peaks should be present)? How would you assign the stretch near 3000 wavenumbers in the IR that you have?
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These assignments are a nightmare. There is simply not enough data here to ID the compound properly.
Do you have a databook with melting points listed to narrow down the search?
Is the melting point a literature value, or determined experimentally by you? Are you confident it is correct?
How was the IR measured - was it a nujol mull? Nujol may be throwing red herrings in here.
How do you know "for a fact" that it is a carboxylic acid?
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I know! Both the IR and H MNR were both pre-given to me, so I have no idea how it was measured. As for the melting point, it was determined experimentally by me, and I am pretty confident with my value. However, to allow for the best possible window of results, I would allow a wiggle room of + or - 5 degrees. I know for a fact that it is a carboxylic acid because my instructor told me so. That's the only reason.
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As for the melting point, it was determined experimentally by me, and I am pretty confident with my value. However, to allow for the best possible window of results, I would allow a wiggle room of + or - 5 degrees. I know for a fact that it is a carboxylic acid because my instructor told me so. That's the only reason.
I'm stumped. The reason I asked about the melting point is that most simple benzoic acids melt much higher (around 200 °C), so it's difficult to think of anything that fits.
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What about unmodified benzoic acid that is very impure?
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What about unmodified benzoic acid that is very impure?
Maybe I suppose. NMR is way off compared to the CDCl3 spectrum, but it's not clear what the solvent in the posted spectrum is.
http://www.sigmaaldrich.com/spectra/fnmr/FNMR000244.PDF
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I am suspicious that an error may have been made. Benzoic acids all seem to be higher melting and the spectra were not obtained by the poster on the sample that had the mp determined. Could one of the provided spectra have been wrong? Certainly the mp was correct, sort of. The NMR is aromatic, but does seem like a benzoic acid, no integral either. I didn't check the IR, but IR seems carboxylic acidish. Could the poster have been given a wrong spectrum? I'd check with the instructor.
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What is the exact wavenumber of the carbonyl resonance around 1700 cm-1?