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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: s30.93a on January 25, 2017, 03:00:30 PM

Title: Which of the following pairs can be distinguished using H-NMR?
Post by: s30.93a 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)
Title: Re: Which of the following pairs can be distinguished using H-NMR?
Post by: Babcock_Hall on January 25, 2017, 05:22:16 PM
Besides chemical shift, what other information is available from NMR spectra?
Title: Re: Which of the following pairs can be distinguished using H-NMR?
Post by: s30.93a 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
Title: Re: Which of the following pairs can be distinguished using H-NMR?
Post by: Babcock_Hall 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.
Title: Re: Which of the following pairs can be distinguished using H-NMR?
Post by: s30.93a 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
Title: Re: Which of the following pairs can be distinguished using H-NMR?
Post by: Babcock_Hall on January 26, 2017, 01:30:20 PM
Therefore, one can distinguish cis versus trans by the magnitude of the coupling constant.