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Anyone good at chemistry? I need some help real quick.

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freezed
Posts: 12973 - Karma: 500
I'm hoping by some strange stroke of luck someone more knowledgeable than I is on here.

I'm trying to interpret an IR spectrum of Eugenol that I took today. I'm having trouble seeing which peak is the phenol (Carbon-Oxygen) stretch. It's supposed to be supposed to be 970-1250 (strong), but in that range there are a bunch of separate peaks. Do I just pick the strongest one or what?


Probably futile posting this on here, but I have to turn this in tomorrow morning. ARGH I hate this class!!
Jan 25 2008 12:20AM
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Tinga
Posts: 11349 - Karma: 2,333
holy shit. good luck with your phd
Jan 25 2008 12:23AM
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HEYLADY
Posts: 572 - Karma: 9
that looks like college material to me i am in high school chem and that does not look like stuff that we were doing on tuesday
Jan 25 2008 12:23AM
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Piste.Off
Posts: 11586 - Karma: 1,860
not very sure but, wouldn't it be the peak that occurs the most?
Jan 25 2008 12:26AM
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Yauch
Posts: 1685 - Karma: 62
hm maybe they all count
Jan 25 2008 12:41AM
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John.
Posts: 1327 - Karma: 11
 No guarantees here, but from what I can see looking in my O chem book it depends on the bond. Carbon-Oxygen double bonds are between 1780-1650 and C-O single bonds are between 1250-1050.

Do you have the molecular formula for the Eugenol? In an alcohol the C-O single bond will be towards the lower end of the interval and higher in a carboxylic acid.
Jan 25 2008 12:55AM
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freezed
Posts: 12973 - Karma: 500
eugenol is C10H12O2... 2-methoxy-4-(2-propenyl)-phenol.

I'm looking at the C-O single bond, I know that, but I'm confused about how I tell which peak represents the absorption of that bond, because 1250-1050 is a broad range with multiple peaks within it.

thanks for the help.
Jan 25 2008 1:01AM
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John.
Posts: 1327 - Karma: 11
The IR spectrum link isn't working for me but maybe this will help:

http://webbook.nist.gov/cgi/cbook.cgi?ID=C97530&Units=SI&Mask=80#IR-Spec

I think you just go with the deepest peak. We haven't covered this yet, so I'm not sure. Good luck.
Jan 25 2008 1:15AM
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Elijah.
Posts: 9322 - Karma: 76
Organic Chem?
Jan 25 2008 1:19AM
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Muteman
Posts: 1508 - Karma: 12
From my experience analyzing IR peaks for aromatic compounds is really difficult. The peak you are describing is right in the range of most other aromatic peaks. Choosing one will be really hard. I think it would be acceptable to point to that region of the spectra and say that it would be located in that range but due to other values occurring in the same region locating a specific peak is not possible without more information.I've never made an IR in lab that didn't have some contaminants and background noise so that is another problem. You correctly identified the peak ranges and that might be the best you can do. You might be able to get more accurate if you can determine which way the peak would shift based on the other pieces of the molecule but whatever. Basically I didn't give any specifics so I'm sorry if that was a waste of time. From my experience though it would be hard to pin pont it. Her eis a link to the spectra if anyone else wants a stab at it.

http://webbook.nist.gov/cgi/cbook.cgi?ID=C97530&Units=SI&Type=IR-SPEC&Index=1#IR-SPEC
Jan 25 2008 1:25AM
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freezed
Posts: 12973 - Karma: 500
yeah, that's probably what I'll have to do. I think have all the other absorptions pinpointed to the right peaks, but like you said, when you do aromatics, it gets pretty messy, especially lower than like 1400/cm wavenumbers. I just don't have enough experience to really use the rest of the molecule to deduce which peak it should be. I could probably do that on an HNMR spectrum, but I really don't know anything about IR spectra...they just made us do this lab without even explaining anything about it.

thanks!
Jan 25 2008 1:38AM
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babysteeze84
Posts: 720 - Karma: 285
Mmmm, and this is why I'm glad I switched from Bio to Anthropology. :) That and I get to dig in the dirt and find 900 year old babies and pottery.
Jan 25 2008 3:11AM
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Red_Shirt
Posts: 292 - Karma: 8
The problem is that the compound's ir band you're looking for is in the fingerprint region, 800-1400, and in there its really hard to find a single band of absorption. I would look at the already established ir spectrum of whatever you want and then just compare the two to see if you're right.
Jan 25 2008 9:13AM
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prosnurfer
Posts: 1842 - Karma: 83
make a graph of the peaks and display it that way. that way u can choose the general range of the highest peaks. then make a essay expanding your reasons.
Jan 25 2008 9:32AM
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skiizy
Posts: 2137 - Karma: 16
believe it depends on the average of the peaks in that range
Feb 5 2008 8:35PM
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Owen.
Posts: 1134 - Karma: 13
I was gonna take chem next year....
but I think you just saved me, thank you
Feb 5 2008 8:39PM
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user098123
Posts: 6072 - Karma: 18
It's not just regular chem don't worry...

but ya, aromatics can be a bitch. I'd just take the smallest range possible that you can.
Feb 5 2008 8:41PM
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freezed
Posts: 12973 - Karma: 500
Yeah I ended up getting it right, thanks for the help guys. And my GC analysis shows my product is 99.6% pure. :) 
Feb 5 2008 8:56PM
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user098123
Posts: 6072 - Karma: 18
Ah nice, gotta love GC.
Feb 5 2008 9:01PM
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Alexander_Keith
Posts: 3204 - Karma: 25

You could get mad dollar peddling the street with that kind of purity.

Feb 6 2008 11:54AM
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RudyGarmisch
Posts: 25443 - Karma: 13,844
Fuck you, I was never able to get above 90% in my labs. Also, O-chem was my second least favorite class, after Biochem.
Feb 6 2008 12:11PM
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