1, what happens when an nuclei with a spin number of ½ is subjected to an applie
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1, what happens when an nuclei with a spin number of ½ is subjected to an applied magnetic field? 2. Recalling that we can have spin up and spin down orientations; what does this diagram suggest about the applied field (%) and the energy separation (AE) of the nuclei? 2 1 2 0 Bo B, Figure 1. https:/www2.chemistry.msu.edu/faculty/reusch/virttxtjmlspectrpy/nmr/nmr1.htm 3. If the nuclei can experience the magnetic field can the electrons? Would the density of the electrons surrounding the nucleus affect what the nucleus feels? 4. We know that the individual signals provided in a classic H-NMR spectra are unique to each chemically-inequivalent hydrogen. Can you provide a reason? 5. Considering the effect of the applied field on a single proton in a molecule and how the electron density impacts this; what might a proton on an adjacent carbon do to the first proton?Explanation / Answer
1. A nucleus with spin number I can have (2 I + 1) possible orientations.Therefore,by using the formulae a nuclei with spin number 1/2 will have 2 possible orientations.In the absence of applied magetic field,both of the possible orientations will have equal energy.However,in the presence of applied magnetic field,the energy levels will split and there is going to exist an energy gap in between the two levels.The spin orientation aligned towards external magnetic field will have lower energy than the spin orientation aligned against external magnetic field.
2. We know that on applying external magetic field,degenerate levels get splitted depending upon whether their spin orientation is towards or against the external magnetic field.The magnitude of the splitting depends upon the the size of the applied magnetic field.
The diagram suggests that when the applied magnetic field is Bx then the energy gap in between the two level is less as compared to the gap when the value of applied magnetic field is greator than Bx.
3. In case of nucleus,its the interaction between the applied magnetic field and spin orientation that plays a major role while in case of electrons,they create their own magnetic field which opposes the external magnetic field.
The density of electron surrounding the nucleus have a huge impact on the way nucleus experience the external magetic field.The magnetic field experienced by nucleus is not equal to the applied magnetic field because the electrons tend to shield the nucleus from the applied field.A magnetic field is produced by electrons around protons which tend to oppose the applied magnetic field.Thereby,reducing the magnitude of the field experienced by proton.
Consider Nucleus A and Nucleus B,nucleus A is having more electron density as compared to nucleus B.Now if we apply identical magentic field to both the nucleus,Nucleus A will experience less amount of magnetic field as compared to nuclues B because in nucleus A,electrons will shield the nucleus to more extent.Thus,more amount of magnetic field need to be applied in case of nucleus A.
4. In a compound, protons can be equivalent or non equivalent depending upon their magnetic environment.Equivalent protons have similar structural environment.Thus,they experience external magnetic field to same extent and lead to single peak in the spectra.On the other hand,Non Equivalent protons do not have identical structural environment.Therefore,they do not experience external magnetic field to same extent and produce different peaks depending upon how many non equivalent protons are present in the compound.
5. By taking under consideration that the protons have different electron density around the nucleus,we can easily predict that they will experience different magnitude of applied magnetic field.In order to explain the affect of a proton on adjacent proton let's take an example of Ethanol,CH3CH2OH wherein two non equivalent hydrogens are present ( look at the structural environment).
As per the spectra of ethanol,Methyl (-CH3) peak is split into triplet which can be explained by looking at the types of spin orientation of Methylene protons (-CH2).There are two methylene protons and both can have two possible orientations either aligned or opposed with respect to applied external field.This leads to four possible (either one is aligned towards or against the applied magnetic field or both are aligned against or towards the applied magnetic field) states out of which two states (both are aligned or opposing the applied external field) can be considered as magnetically equivalent combination.Thus,methyl (-CH3) protons's peak gets splitted into a triplet.Similarly by making combinations for the methyl protons,we can predict how the peak of methylene protons is getting splitted.
NOTE - Once you're done making all the combination,look out for the magnetically equivalent combinations and then predict the splitting of the peak.Also, (n+1) rule exists which can easily predict the multiplicity of multiplet by putting the value of n as the number of equivalent protons in the neighbouring atom.
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