What are the key steps to analyzing an NMR spectrum?

In summary: Additionally, the shift difference and multiplicity are not provided, so you would also be lost trying to calculate them.
  • #1
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.
 
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  • #2
Mentors: the image of the NMR spectrum is not attached to this post. Therefore, it's essentially impossible to solve.
 

1. What is NMR spectra analysis?

NMR spectra analysis is a technique used in chemistry and biochemistry to study the structure and properties of molecules. It involves measuring the energy released by the nuclear spins of atoms in a molecule when they are placed in a strong magnetic field. This information can then be used to determine the chemical structure and composition of a molecule.

2. How does NMR spectra analysis work?

NMR spectra analysis works by subjecting a sample of a molecule to a strong magnetic field and then applying a radio frequency pulse to the sample. This pulse causes the nuclear spins of the atoms in the molecule to absorb energy and then release it in the form of a signal. The resulting NMR spectrum is a graph showing the frequencies at which these signals occur, which can be used to identify the atoms and their chemical environments within the molecule.

3. What can NMR spectra analysis tell us about a molecule?

NMR spectra analysis can provide valuable information about the structure, composition, and dynamics of a molecule. It can reveal the number of atoms in a molecule, their connectivity, and the types of chemical bonds present. It can also provide insight into the stereochemistry and conformational changes of a molecule, as well as its purity and stability.

4. What are the applications of NMR spectra analysis?

NMR spectra analysis has a wide range of applications in various fields, including organic and inorganic chemistry, biochemistry, pharmaceuticals, and materials science. It is commonly used for compound identification, purity testing, quality control, and studying reaction mechanisms. It can also be used for protein structure determination, drug discovery, and environmental analysis.

5. Are there any limitations to NMR spectra analysis?

While NMR spectra analysis is a powerful tool, it does have some limitations. It requires a relatively large sample size, typically on the order of milligrams, and may not be suitable for analyzing complex mixtures. It also requires specialized equipment and expertise, making it a more expensive technique compared to other analytical methods. Additionally, certain types of molecules, such as those with low molecular weight or lacking hydrogen atoms, may not produce useful NMR spectra.

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