Why is the NMR multiplicity incorrect in some places?

In summary, the conversation discusses a question regarding determining the structure based on a molecular formula and NMR spectrum. The answer is questioned and it is determined that the assignment is incorrect, as evidenced by other sources showing a different result.
  • #1
etotheipi
I was doing a question that wanted you to determine the structure given a molecular formula and an NMR spectrum. The following was the answer:
1583685998403.png

I'm unsure as to how the multiplicities were obtained. For ##X##, the neighbouring carbon ##Y## has 2 hydrogens, so this peak is a triplet (OK so far!).

But for ##Y##, the neighbouring carbon (##X##?) has 3 hydrogens so shouldn't that peak should be a quartet? And ##Z##'s neighbouring carbon has no hydrogens so this peak should just be a singlet. This also agrees with the integration, since both ##X## and ##Z## have 3 hydrogens but ##Y## only has 2. I am not sure why they have put it the other way around?

Thank you!
 
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  • #2
I agree with you argumentation. It looks like the assignment is wrong.
 
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  • #3
DrStupid said:
I agree with you argumentation. It looks like the assignment is wrong.

Ah, awesome. Vindication!
 
  • #4
It’s wrong online in some places as well. This is the wrong assignment!
https://physics.bgu.ac.il/COURSES/LAB_C/NMR/htbooks/nmr/spectra/mek-016.gif
 
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FAQ: Why is the NMR multiplicity incorrect in some places?

1. What is NMR multiplicity?

NMR multiplicity refers to the number of peaks observed in a nuclear magnetic resonance (NMR) spectrum. It is determined by the number of neighboring hydrogen atoms that are chemically equivalent to the hydrogen being observed.

2. How is NMR multiplicity calculated?

NMR multiplicity is calculated using the n+1 rule, where n represents the number of neighboring hydrogen atoms. This rule states that the number of peaks in a multiplet will be equal to n+1. For example, a hydrogen with 3 neighboring hydrogens will have a quartet (3+1=4) in its NMR spectrum.

3. Why is NMR multiplicity important?

NMR multiplicity provides valuable information about the structure and environment of molecules. It can help identify the number of neighboring atoms, the type of bonding present, and the symmetry of the molecule.

4. How does NMR multiplicity differ for different nuclei?

The n+1 rule used to calculate NMR multiplicity is specific to hydrogen atoms. For other nuclei, such as carbon or nitrogen, the multiplicity is determined by the number of chemically equivalent nuclei that are directly bonded to the observed nucleus.

5. Can NMR multiplicity be used to determine the identity of a compound?

NMR multiplicity alone cannot determine the identity of a compound, but it can provide important clues. By comparing the multiplicity and chemical shifts of peaks in a spectrum to known values, it can help identify the functional groups present in a molecule.

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