spirocycle
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Need help with IR spec reading
In orgo class, we had to take an IR spec of our eugenol product and determine its structure.
There are so many freakin peeks, and this is my first one so I am having a real hard time reading it.
based on the boiling behavior, I assume there is little to no DCM left in the sample (no boiling at 55 c), but based on the viscosity and RI, there is
not likely significant quantities of water (recorded 1.5267 and the reported value is 1.5410
<http://chemicalland21.com/specialtychem/perchem/EUGENOL.htm>
and since it is not miscible with water, and there was no visible interphase, I think its safe to assume it was very dry.
But it was still a very, runny clear liquid, which is not typical according to my chem teacher.
anyway, here is the printout
I have circled the two peaks that I think I identified, and I think that the wide section aroudn 3529 is indicitive of c-o bonding
thanks for helping!
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DJF90
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For a start, don't worry about the region below 1000 cm^-1 - this is termed the "fingerprint region" and is rather specific to the compound. What IR
spec is good at is identifying functional groups in your molecule. The broad peak at 3529 cm^-1 is due to the phenolic OH (this region is also active
for alcohols), and that at 2845 is likely to be your aldehyde C=O stretch. That at 2935cm^-1 is likely to be your terminal alkene. The peaks in the
700-900cm^-1 range are likely to be due to the benzene ring. Peaks in the region 1200-1260 will be due to the phenol again and the phenol and methyl
ether C-O stretches.
[Edited on 23-10-2010 by DJF90]
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spirocycle
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there is no aldehyde in eugenol, or any other solvents used in the extraction.
also, what peaks would show the allyl group?
and what does that giant peak just over 1500 signify?
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Nicodem
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The first thing to do is to verify that your spectra fits that of eugenol. You can find the IR spectra of eugenol at SDBS. Next, if you want to assign peaks, you can compare them to a table of characteristic IR peaks. Here is one such table (by clicking the links on the table you get to more detailed info). But you should be aware that IR spectra can not and
should not be used alone to unambiguously determine the functional groups and structural elements present in the compound. You should have other
spectroscopic data as well to determine anything with some proper certainty. But since by comparing with literature spectra you already know the
identity of the compound, you can now practice assigning frequencies to the bonds vibrations and stretching using the above linked table.
[Edited on 25/10/2010 by Nicodem]
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DDTea
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Quote: Originally posted by spirocycle  | there is no aldehyde in eugenol, or any other solvents used in the extraction.
also, what peaks would show the allyl group?
and what does that giant peak just over 1500 signify?
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1500cm<sup>-1</sup> + 1430cm<sup>-1</sup> are your benzene "fangs." If you're good at reading spectra (and I'm not), you can
use the peaks between 1500 and 2000 cm<sup>-1</sup> to find the substitution pattern of the benzene ring.
That's one of those functional groups that you should always look for; fortunately it's pretty obvious (in most cases).
I don't see an aldehyde carbonyl in this spectrum (and again, this is another obvious peak).
For allyl, you would see the C=C bond stretch (that should be your short peak around 1760) and sp<sup>2</sup> C-H bond symmetric +
asymmetric stretches + scissoring.
Of course, as Nicodem said, relying on IR alone to determine structure is not wise. It would be good to compare your spectrum to a spectral database.
"In the end the proud scientist or philosopher who cannot be bothered to make his thought accessible has no choice but to retire to the heights in
which dwell the Great Misunderstood and the Great Ignored, there to rail in Olympic superiority at the folly of mankind." - Reginald Kapp.
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DJF90
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Haha oops getting confused between Eugenol and Vanillin... my bad!
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chemrox
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@Nicodem what does one have to do to view this page? I get a big red slash "forbidden" graphic.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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chemrox
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and every other published link leads me to sites in Japanese or pdf shot of the english language portal
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Nicodem
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The link should work now. Next time please search for the spectra manually. It only takes 15 seconds, which is less than I need to find it again and
then edit the post.
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