May 25, 2019, 09:48:53 AM
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Topic: Which of the following pairs can be distinguished using H-NMR?  (Read 2685 times)

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Offline s30.93a

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Which of the following pairs can be distinguished using H-NMR?
« on: January 25, 2017, 03:00:30 PM »
1. both the H are chemically and magnetically equivalent thus will split into singlet and we can't distinguish between the two spectra and tell which is trans or cis
2. each H will split as doublet(vinyl), doublet of quartet (vinyl and on same carbon having methyl) and doublet (methyl) but I don't know whether we can predict for cis or trans
Note: splitting of aromatic H are ignored.
Please check the above solution for (1) and further guide for (2)

Offline Babcock_Hall

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Re: Which of the following pairs can be distinguished using H-NMR?
« Reply #1 on: January 25, 2017, 05:22:16 PM »
Besides chemical shift, what other information is available from NMR spectra?

Offline s30.93a

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Re: Which of the following pairs can be distinguished using H-NMR?
« Reply #2 on: January 26, 2017, 04:40:01 AM »
1. J value can be roughly estimated
2. area under the curve will tell no of H
3. no. of peaks will tell how many adjacent H are present to split it

Offline Babcock_Hall

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Re: Which of the following pairs can be distinguished using H-NMR?
« Reply #3 on: January 26, 2017, 10:13:53 AM »
With respect to 1, I am not sure what you mean by roughly estimated.  Also with respect to 1, have you heard of the Karplus relationships?  These govern the value of coupling constants as a function of the dihedral angle between the two nuclei.

Offline s30.93a

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Re: Which of the following pairs can be distinguished using H-NMR?
« Reply #4 on: January 26, 2017, 12:49:20 PM »
yes i knew that formula, by roughly estimation I mean we can compare width between the peaks and thus deduce what is the intensity of splitting, as J(trans)>J(cis) that can be seen in spectra

Offline Babcock_Hall

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Re: Which of the following pairs can be distinguished using H-NMR?
« Reply #5 on: January 26, 2017, 01:30:20 PM »
Therefore, one can distinguish cis versus trans by the magnitude of the coupling constant.

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