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Topic: NMR Maleic & Fumaric Acid  (Read 993 times)

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Offline Der-Ubermensch

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NMR Maleic & Fumaric Acid
« on: April 13, 2020, 08:27:06 AM »
Hello, I just wanted to know why the chemical shift of hydrogen in the fumaric acid is 6.6 ppm and for maleic acid it's 6.3 ppm. Hydrogen are much closer to COOH in the fumaric acid ?
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Offline Babcock_Hall

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Re: NMR Maleic & Fumaric Acid
« Reply #1 on: April 13, 2020, 08:12:04 PM »
What makes you think that the hydrogens are closer in fumaric acid?  Do you mean in a through-space sense or a through-bond sense?
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Offline Der-Ubermensch

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Re: NMR Maleic & Fumaric Acid
« Reply #2 on: April 13, 2020, 09:10:04 PM »
I said that hydrogen are much closer in the fumaric acid because I saw this in a correction, but it's seem silly to me. But I don't know how to justify that hydrogen in the fumaric acid are more "unblinded" (déblindé in french).

(sorry for my english)
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Offline Babcock_Hall

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Re: NMR Maleic & Fumaric Acid
« Reply #3 on: April 15, 2020, 07:51:14 AM »
https://www.chem.wisc.edu/areas/reich/chem605/index.htm
I don't know the explanation.  However you might want to go to eh CHM 605 site at the University of Wisconsin and go to the section, "9.61 Parameters for Calculating Vinyl Chemical Shifts."  There are Z values given for estimating the chemical shifts on vinyl hydrogens.
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