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Topic: How to deduce the structure base on the information?  (Read 14608 times)

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Offline kwokmern

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How to deduce the structure base on the information?
« on: October 13, 2009, 09:44:17 AM »


I have tried for a few nights but to no avail~~ please would any kind soul out there help me....thank you~

I am unable to post any pictures, dunno y~ but the link to the NMR spectrum is http://www.flickr.com/photos/43535308@N04/4007785225/

Please help~~thanks

Offline DrCMS

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Re: How to deduce the structure base on the information?
« Reply #1 on: October 13, 2009, 10:11:34 AM »
Seems quite simple.

What have you got so far.

Offline kwokmern

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Re: How to deduce the structure base on the information?
« Reply #2 on: October 14, 2009, 10:58:46 AM »
I've just begined learning on these spectrum stuff, and i've drawn all isotopes base on the given structure, but non of it satisfy the spectrum. Maybe some of it satisfy the spectrum but i'm not knowledable to understand...I've drawn alcohol, ethers, and tried combination.....e.g, CH3-Ch2-O-CH2-CH2-CH3...

Offline DrCMS

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Re: How to deduce the structure base on the information?
« Reply #3 on: October 14, 2009, 12:29:00 PM »
Look at the intergration of the proton NMR you have:
6H doublet 
2H quartet
1H multiplet
1H broad singlet
2H triplet

What do these peak types and intergrations tell you about the groups in the structure?
What do the chemical shift of these peaks tell you?

In the Carbon 13 NMR you have
CH3 1 peak
CH 1 peak
CH2 - 2 different peaks
What do these peak types tell you about the groups in the structure?

In the IR you have a large broad absorption at 3341 wavenumbers.
What does that type of peak indicate?

You know the structure is C5H12O  what possible stuctures match the data?



Offline kwokmern

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Re: How to deduce the structure base on the information?
« Reply #4 on: October 15, 2009, 01:35:11 PM »
Hi,
I think this is the nearest to the spectrum, but i'm not sure. Please advise if it satisfy the spectrum~ thanks~

http://www.flickr.com/photos/43535308@N04/4014037367/in/photostream/

Offline sjb

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Re: How to deduce the structure base on the information?
« Reply #5 on: October 15, 2009, 03:04:03 PM »
OK, here's the structure you've drawn.

Whilst it matches in terms of the 6H peak, not much else seems to correspond. Can you see that the compound you have drawn will have a 3H singlet, as well as a 2H doublet and a 1H multiplet?

What does having a broad singlet integrating to 1H suggest, together with your IR?

Offline kwokmern

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Re: How to deduce the structure base on the information?
« Reply #6 on: October 16, 2009, 12:44:24 PM »
IR spectrum at 3341 wavenumber normally indicate the presence of OH group and possibly terminal alkynes group. But due to "sharp" feature, OH group has to be eliminated and for terminal alkynes group there is suppose to be another peak at around 2200 wavenumber due to the triple bond, which is not seen in the graph.

Broad singlet integrating to 1H would indicate 1 proton with no other proton beside it for coupling

Offline DrCMS

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Re: How to deduce the structure base on the information?
« Reply #7 on: October 16, 2009, 04:12:32 PM »
If you think the IR peak in question is "sharp" you need to think again about what sharp means or get new glasses. 
It is a broad peak indicative of an OH group and the broad singlet in the proton NMR is for the H in the OH.

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