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Author Topic: i need help with identifying a molecule  (Read 5631 times)

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anoymous

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i need help with identifying a molecule
« on: May 25, 2017, 06:37:13 AM »

so for the course spectroscopic methods, we had to make a 1H-NMR, IR and UV-vis, and we got a COSY and a 13C-NMR
the deadline is monday
these are the spectra (sorry idk how to embed if it is possible to embed):

IR:



H-NMR (+zooms):









C-NMR:



UV-VIS:

https://puu.sh/w0LGl/476f69484a.png

it was greenish and solid
b4 anyone asks: we didnt get a molar mass
thanks in advance

we already identified a part of the molecule (or at least we think we did):
para substituted acetophenone
« Last Edit: May 26, 2017, 09:14:55 PM by Dan »
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wildfyr

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Re: i need help with identifying a molecule
« Reply #1 on: May 25, 2017, 02:35:03 PM »

I gave a crack at it with the NMR and IR spectra and couldn't come up with anything I liked.  I will say though... how can something be greenish and have no absorbance in the visible spectrum?

Not a big fan of interpreting a 1640 cm-1 IR peak as acetophenone either. Usually thats an amide, but I dont see an amide proton. Mass spec would be hella useful.
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clarkstill

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Re: i need help with identifying a molecule
« Reply #2 on: May 25, 2017, 09:17:24 PM »

It looks like there's an allyl group in there somewhere...
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anoymous

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Re: i need help with identifying a molecule
« Reply #3 on: May 25, 2017, 11:42:53 PM »

I gave a crack at it with the NMR and IR spectra and couldn't come up with anything I liked.  I will say though... how can something be greenish and have no absorbance in the visible spectrum?

Not a big fan of interpreting a 1640 cm-1 IR peak as acetophenone either. Usually thats an amide, but I dont see an amide proton. Mass spec would be hella useful.
conjugated carbonyl can be around that region in IR
the main reason why we thought about acetophenone is bc the signals at 198 ppm for the carbonyl carbon, 26 ppm for the methyl carbon and 2.6 for the methyl hydrogens fit perfectly for an aceto group directly on a benzene. we compared with other spectra containing acetophenone and used calculation software, all of the different molecules and all the calculation programs gave the same signals for that aceto group
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Dan

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Re: i need help with identifying a molecule
« Reply #4 on: May 26, 2017, 09:08:48 PM »

(sorry idk how to embed if it is possible to embed):

You need to put the image url in img tags, like this:

Code: [Select]
[img]website.com/image.ext[/img] 
I have edited your post.
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anoymous

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Re: i need help with identifying a molecule
« Reply #5 on: May 27, 2017, 12:17:49 AM »

(sorry idk how to embed if it is possible to embed):

You need to put the image url in img tags, like this:

Code: [Select]
[img]website.com/image.ext[/img] 
I have edited your post.
thanks!
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wildfyr

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Re: i need help with identifying a molecule
« Reply #6 on: May 27, 2017, 12:06:06 PM »

Sdbs says acetophnone is 1690. http://www2.ups.edu/faculty/hanson/Spectroscopy/IR/I is a good IR reference. 1680-1700 for aryl ketones. Even benzophenone isn't all the way down at 1640. Your singlet on a methyl could be a methyl on benzene, it shows up in similar spots in 1H and carbon. For me the hardest to square up is that multiplet (sextet?) on 1 proton. It's down where, as clarkstill pointed out you might see allyl, but a normal allyl has a highly characteristic splitting of two doublets at about 5 and 5.5 and a multiplet at 6, all on 1 H.


« Last Edit: May 27, 2017, 12:17:44 PM by wildfyr »
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anoymous

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Re: i need help with identifying a molecule
« Reply #7 on: May 28, 2017, 05:58:32 AM »

Sdbs says acetophnone is 1690. http://www2.ups.edu/faculty/hanson/Spectroscopy/IR/I is a good IR reference. 1680-1700 for aryl ketones. Even benzophenone isn't all the way down at 1640. Your singlet on a methyl could be a methyl on benzene, it shows up in similar spots in 1H and carbon. For me the hardest to square up is that multiplet (sextet?) on 1 proton. It's down where, as clarkstill pointed out you might see allyl, but a normal allyl has a highly characteristic splitting of two doublets at about 5 and 5.5 and a multiplet at 6, all on 1 H.
those exact values can change depending on what kind of IR
check the NMR values for the aceto group in acetophenone (both carbons+the hydrogens) and compare it to our values, and you'll see that the values fit nearly perfectly


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wildfyr

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Re: i need help with identifying a molecule
« Reply #8 on: May 28, 2017, 11:33:40 AM »

I've never seen an IR value change more than about 5 based on doing neat ATR, nujol mull, KBr pellet etc. You came here for help, I've run 1000+ IR spectra and NMRs in my life. I agree that the those few NMR signals match well, but prediction software is not intended to be exact.

Here is a thought: there is a very strong peak at 813, which is just about half of 1640, perhaps that is just an overtone, and there is no carbonyl species at all.

Humor me and see how Para allyl toluene (or perhaps allyloxy?)   fits if you make that assumption.

This is an altogether tough one, I'm sorry.
« Last Edit: May 28, 2017, 11:49:48 AM by wildfyr »
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wildfyr

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Re: i need help with identifying a molecule
« Reply #9 on: May 28, 2017, 11:37:53 AM »

And please come back and let me know what it ends up being, I spent like an hour working on this and I'm damned curious.
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anoymous

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Re: i need help with identifying a molecule
« Reply #10 on: May 28, 2017, 12:16:41 PM »

I've never seen an IR value change more than about 5 based on doing neat ATR, nujol mull, KBr pellet etc. You came here for help, I've run 1000+ IR spectra and NMRs in my life. I agree that the those few NMR signals match well, but prediction software is not intended to be exact.

Here is a thought: there is a very strong peak at 813, which is just about half of 1640, perhaps that is just an overtone, and there is no carbonyl species at all.

Humor me and see how Para allyl toluene (or perhaps allyloxy?)   fits if you make that assumption.

This is an altogether tough one, I'm sorry.
it isnt only in the predicted spectra tho
it also shows up for every regular spectrum we found
and how would you otherwise explain that carbon nmr signal at 198? by my knowledge, that can only be a carbonyl, and even then only an aldehyde or ketone (and we clearly dont have an aldehyde when we look at the proton nmr)
dont get me wrong
i welcome the thought it would be something else
i just dont know what it could possibly be
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wildfyr

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Re: i need help with identifying a molecule
« Reply #11 on: May 28, 2017, 02:00:25 PM »

So the guess is Para allyl acetophenone?
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anoymous

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Re: i need help with identifying a molecule
« Reply #12 on: May 28, 2017, 08:59:43 PM »

So the guess is Para allyl acetophenone?
unless you know something else that has a peak in the carbon spectrum at 198 ppm, yes
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wildfyr

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Re: i need help with identifying a molecule
« Reply #13 on: May 29, 2017, 11:23:28 AM »

I dig some deep digging and found this paper http://pubs.acs.org/doi/abs/10.1021/ja00252a029 by Stille. In it, they do a bunch of Stille couplings and one of them gives a mix of 4-(2-Propenyl)acetophenone #4 and (E)-4-(l-propenyl)acetophenone
#5. Our guess for your HW is #4.

1H NMR (270 MHz)

7.89 (d, J = 8.3 Hz, 2 H, 4), 7.88 (d, J = 8.3 Hz, 2 H, 5), 7.38 (d, J= 8.4 Hz, 2 H, 5), 7.27 (d, J = 8.2 Hz, 4), 6.41 (m, 2 H, 5), 5.94 (m. 1 H, 4), 5.13-5.06 (m, 2 H, 4), 3.43 (d, J = 6.7 Hz, 2 H, 4), 2.57 (s, 3H, 4), 2.53 (s, 3 H, 5), 1.91 (d, J = 5.0 Hz, 3 H, 5).

It fits pretty well, except your benzene ring is at 6.91 not 7.27, and your peaks at 5.1 are doublets unless your squint reeeaaalll hard. Hope this extra info helps.
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anoymous

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Re: i need help with identifying a molecule
« Reply #14 on: May 30, 2017, 04:19:39 AM »

that fits indeed very well for the HNMR, but we seem to have 2 extra carbon signals (a quaternary at 159 ppm and then a signal from a double bonded carbon)
any idea where those might come from?
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