Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: meepin on July 11, 2013, 10:33:50 PM

Title: NMR help
Post by: meepin on July 11, 2013, 10:33:50 PM

Hi all, I'm struggling a bit with this NMR assignment.

Here is the structure:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FkpvS2FD.jpg&hash=2a7aa26c25cc41bb1647b492c73b2bc6937030b8)

Here is the H NMR
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FL1ZWpKj.jpg&hash=0741ba664974aaf7e86e64595108ef9d7bf4c056)

I'm guessing the COOH (a) isn't shown because of deuterium exchange.

I'm guessing b would be at 7.7 b/c it's so close to an EN group. Then c would be at 7.5.

6.9 would represent e and g. They would be shifted downfield because of the methoxy group.

6.3 would represent d and f...because those are the only ones left.

h is at 3.832 b/c it's the only one representing 3 Hs due to integration.

Because e and g are equivalent, they would appear at the same spot and still be simply counted as a doublet right? same for d and f? Thanks in advance for anyone's input!

Mod edit: img tags added to display images. Please either upload images as attachments or put the image uri in [img][/img] tags rather than linking to external websites. More information on formatting posts here (http://www.chemicalforums.com/index.php?topic=59314.0).

Title: Re: NMR help
Post by: Dan on July 12, 2013, 06:52:30 AM

Hint: Pay attention to the coupling constants.

Title: Re: NMR help
Post by: meepin on July 13, 2013, 11:55:05 PM

Quote from: Dan on July 12, 2013, 06:52:30 AM

Hint: Pay attention to the coupling constants.

I'm afraid I don't understand - how would coupling constants help?

Title: Re: NMR help
Post by: Dan on July 14, 2013, 06:17:59 AM

If A couples to B with J = X Hz, then B couples to A with J = X Hz.

i.e. the signals for Hs that couple to each other should have matching coupling constants.