Topic: Unusual splitting (or lack thereof) in 1H NMR Problem (Read 5167 times)

combatwombat · « **on:** March 08, 2009, 07:47:16 PM »

A compound has the formula C₈H₁₄O₄. Its 1H NMR spectrum shows the following features: 6H triplet at 1.2 ppm; 4H singlet at 2.5 ppm, and 4H quartet at 4.1 ppm. IR spec shows a peak at 1740 cm-1 (i.e. ester or lactone).

These are the two structures I came up with - the top one is correct, but I don't see how the 4 protons in the middle could possible produce a 4H singlet. Seems like they'd have to be a 4H doublet. Also - why the 2nd one doesn't fit the data as well?

nj_bartel · « **Reply #1 on:** March 08, 2009, 08:16:39 PM »

If they were to cause a 4-H doublet, they'd have to somehow be both identical and different, as you're integrating them together yet saying they also couple because there are no other adjacent protons. Those protons you circled are in fact identical - rotate half the molecule so the carbonyl oxygens are facing the same direction.

combatwombat · « **Reply #2 on:** March 08, 2009, 09:41:43 PM »

They are identical? OK... Still seems like they should be splitting each other. Each set of 2 hydrogens has an adjacent set of 2 hydrogens that should be splitting them... or so I thought

nj_bartel · « **Reply #3 on:** March 08, 2009, 11:13:04 PM »

http://img18.imageshack.us/my.php?image=helpnmr.jpg

That should make it more clear.

Topic: Unusual splitting (or lack thereof) in 1H NMR Problem (Read 5167 times)

combatwombat

Unusual splitting (or lack thereof) in 1H NMR Problem

nj_bartel

Re: Unusual splitting (or lack thereof) in 1H NMR Problem

combatwombat

Re: Unusual splitting (or lack thereof) in 1H NMR Problem

nj_bartel

Re: Unusual splitting (or lack thereof) in 1H NMR Problem

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