What are the key steps to analyzing an NMR spectrum?

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SUMMARY

The discussion focuses on analyzing a 400 MHz NMR spectrum, specifically determining chemical shifts, integrated intensities, proton types, multiplicities, coupling constants (J), and the number of protons on adjacent atoms. Key techniques mentioned include the ratio of integrals for peak identification and the application of the (n+1) rule for predicting multiplicity. The user expresses confusion regarding the interpretation of split peaks and the calculation of coupling constants, particularly for doublets and quintets. The absence of the NMR spectrum image hinders accurate analysis and resolution of the user's queries.

PREREQUISITES
  • Understanding of NMR spectroscopy principles
  • Familiarity with chemical shift values and their significance
  • Knowledge of the (n+1) rule for multiplicity determination
  • Ability to calculate coupling constants (J) in NMR
NEXT STEPS
  • Research the interpretation of NMR spectra, focusing on peak splitting and multiplicity
  • Learn how to accurately calculate coupling constants (J) for various peak types
  • Study the significance of integrated intensities in determining hydrogen counts
  • Explore advanced NMR techniques for analyzing complex spectra
USEFUL FOR

Chemistry students, organic chemists, and researchers involved in NMR spectroscopy analysis will benefit from this discussion.

Foghorn
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Homework Statement



Determine the chemical shift, integrated intensity, proton type, multiplicity, J (Hz), and # of protons on the adjacent atoms for this spectra given a 400 MHz NMR.

http://img411.imageshack.us/img411/7629/chem262lnmr1.png

Homework Equations



(n+1) rule?
(n+1) x (m+1) rule?

J = shift difference x NMR MHz

The Attempt at a Solution



Sup,

I'm having trouble analyzing an NMR spectrum of the aforementioned compound. Namely, I'm provided a spectrum with only 5 sets of peaks, but I'm sure it has 7 groups of heterotopic hydrogens.

First, I calculated the ratio of integrals to each other, which I hoped would give me the number of hydrogens represented by each region. 2:1:1:2:3. I have no idea if that's even a correct technique, but it helped me confirm several things. The first peak, upfield at around 2.277 ppm is the methyl group; I've determined that. From there, I'm slightly lost. The singlet at 4.679 ppm is probably the AR-O-CH2, since its integrated intensity corresponds to a ratio of 2 hydrogens.

After that, I'm confused as to why there are so many split peaks. The doublet could correspond to carbon #3's hydrogen adjacent to the methyl group, since the (n+1) rule is followed. Following that, no clue. For example, how could a quintet be produced here? Is it actually a quartet with the singlet from the hydroxyl group of the acid?

Finally, how could I measure the coupling constant (J) for these peaks? A doublet is just the difference between the two peaks (ppm) multiplied by the MHz of the machine (400 MHz in this case), the triplet is the difference of the inner peak and an outer peak multiplied by MHZ (do I provide the range? or just pick one of the differences?); does the same principle apply for the quintet, i.e. find the difference between the inner peak and an outer peak? And singlets do not have a coupling constant, correct?

As you can tell, I am thoroughly confused.

It seems to me that all of the hydrogens are unique. There are no equivalent hydrogens, except those bonded to the same carbon.
 
Last edited by a moderator:
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Mentors: the image of the NMR spectrum is not attached to this post. Therefore, it's essentially impossible to solve.
 

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