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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: smghz on February 19, 2018, 10:48:11 AM

Title: 1H NMR question
Post by: smghz on February 19, 2018, 10:48:11 AM
I've been struggling a bit with this NMR interpretation problem. There is this pair of 2.00 that are just frustrating, as well as that 5.68 that I round to 6 H's. I would love to know any insight about this. The molecule is trans-9-(2-phenylethenyl)anthracene.
(https://ibin.co/w800/3sHqICV843Al.png)
Title: Frustrating 13C NMR problem
Post by: smghz on February 19, 2018, 10:51:04 AM
For one reason or another, this may be the most frustrating NMR spectrum I have seen. I honestly do not know where to begin. There are no halides or electronegative atoms that make it easier to find those carbons deshielded v. shielded. Only aromatics. And I do not know any pattern about carbons in aromatic rings. Can someone help me read this and match the peaks? I can definitely find out the integration, splitting, etc., but matching the peaks has been just mind boggling.

(https://ibin.co/w800/3sHrI1I1uNMe.png)
Title: Re: Frustrating 13C NMR problem
Post by: hypervalent_iodine on February 19, 2018, 12:51:16 PM
In general, quaternary carbons tend to have a lower intensity that other carbons, so you could start there. Its there any particular reason you have to assign all of them? It seems like a lot of wasted effort and mental strain to me.
Title: Re: 1H NMR question
Post by: billnotgatez on February 19, 2018, 01:14:30 PM
@smghz
I have merged your post that were alike

We only post a given question once on the forum.
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http://www.chemicalforums.com/index.php?topic=65859.0 (http://www.chemicalforums.com/index.php?topic=65859.0)
Title: Re: 1H NMR question
Post by: wildfyr on February 19, 2018, 01:35:36 PM
I think you could get some really useful places to start by using the SDBS database. Perhaps look up styrene and methyl anthracene, just to get you moving. Its a powerful resource. And I agree this is a very stupid exercise in bashing a student's head against the wall. You can learn just as much from structures that give clearer splittings and shifts.

http://sdbs.db.aist.go.jp/sdbs/cgi-bin/cre_index.cgi
Title: Re: 1H NMR question
Post by: clarkstill on February 19, 2018, 08:45:06 PM
Bear in mind that the pair of hydrogens you've circled in yellow aren't magnetically equivalent, nor are the pair in the pink circle. However, there is a mirror plane down the middle of the anthracene unit, so hydrogens on opposite sides of the anthracene that are linked by the mirror plane are magnetically equivalent.

That said, without 2D data (COSY, HSQC, HMBC) I'm not convinced its possible to assign this unambiguously.
Title: Re: 1H NMR question
Post by: kriggy on February 20, 2018, 01:41:56 AM
Yeah, get some 2D and you will be fine. You can clearly identify the hydrogens.
BTW what solvent did you use for the experiment? Because the signal at 7.2x that is not integrated looks very much like CDCl3 peak.