NMR
Emitted energy is wha tis captured to get NMR.
NMR is used for multiple tasks like structural confirmation, structural elucidation, and mechanistic studies.
Principle: Magenetic moment is denoted by “I” when it comes to proton NMR. For electrons it is knw as “ESR” but is not as strong as proton so thats why we use NMR. I should not be equal to 0 in order for. When protons and neutrons are both equal then the NMR is inactive. If one is odd and the other is even then it is inactive.
proton + neutron = mass. Mass number can very, so Isotopes
proton = atomic number
H1, H2, H3(Triturium) is an isotope that is usually not used because theres not much abundance.
What is inside an NMR machine?
A big ass superconducting magnet. Immersed in helium, which tempature is -269C which is what makes it superconducting and liquid nitrogen at tempature 196C.
A console that sends and receive information
During the spin, the magnetic momoment is spinning perpendicular. When atoms have no magenetic field and then subjected to a magnetic field it is known as B(0). The atoms then align. Magnetic field directly affects the distance between the alpha and beta spin state. The energy from the radio frequency also inclfuence when the splitting occured. The stronger the magenetic field the stronger the energy difference.
Circulating electrons oppose the magenetic field. This is known as shield.
When the alpha spins flip to beta flips and the energy is absorbed this is known as resonance.
Deuterated solvent is used to dissolve your sample and put into the NMR machine.
How to read a NMR signal:
The peaks show how many type of protons, the intensity will show the length, the position of signals show the types of protons. Splitting pattern only occurs when the hydrogens of neighboring patterns interact with each other.
Chemical Shift
Deshielded: proton that is getting its negativity pulled from it. Moving Downfield
Shielded: proton that is getting its negativity pushed to it. Moving Upfield
Even though MegaHertz is the radio frequency energy provided the difference between alpha and beta spin is Hertz but we just quantify it by ppm. Silicon is always positive, so the methyls are so shielded so the shift goes to 0. This is why TMS is used as the reference peak for NMR machines.
Carboxylic Acid is the most electronegative and the chemical chift is between 10-13 because the Hydrogen attached has no electrons spinning around it meaning has nothing blocking the magnetic shield.
Anistropy is the next lesson. Read over this omx
3/4/25
Benzene ring - the protons in the ring are delocalized which is what creates the cirlce that we draw in the ring. In the benze ring, the electrons circulating in the ring aligns with the magentific field so when you apply 100 mghz, the ring will experience 110 mghz because it aligns with the magnetic field aligning. This is known as aromatic deshielding affect. This also occurs to double bonds as well. The chemical shift range is ~6-8.5 ppm. This concept is known as Anistropy.
For example Annulene - the protons around the ring are deshielded while the protons in the ring are shielded because of the magnetic moment that is occuring.
Alkyne(triple bond) moments
This electron density also opposes the field. If the field is horizontal, the alkyne is perpendicular. Range is 2.5.
For proton NMR the rand is from 0-12 ppm.
Chemical Equivalence
Symmetry operation - axis of symmetry/plane of symmetry. If an atom
Fast intramolecular dynamic process - Chemical tautomerization or if the bond rotates quickly.
Homotopic- when you can split a compound in half and the protons have identical environments
Enantiotopic- when 2 hydrogens are enantiomers of each other.
If protons are not homotopic or enantiotopic then they are not chemically equivalent.
Where there are 2 protons on a chiral center, they are NEVER chemically equivalent due to the chiral center. Unless there is axis symmetry or plane symmetry.
Integration
The length of the peak is dependent on how many protons are in that type of peak. Integration values - basically finding the amount of of how many protons is in a peak.
Splitting
Multiple pssibilities. The peak length is splitting is dependent on the multilpe possibilies of the neighboring protons
Simple rule: N + 1. Number of neighboring protons that are chemically equivalent .
Hydrogen on Hydroxy groups keeps exchanging so it is not usually counted.
Coupling Constant
The degree to which a proton will couple to its neighboring proton, is called a couple constant, or J value. J value is the distance between the splitting of doublets, triplets, and so on.
Doublet of doublet is when there are more than 1 different neighboring protons.
13 Carbon NMR
Carbon-Carbon interaction does not occur because Carbon 13 is not abundant(1%) and most likely, there is not 2 Carbon 13s next to each other. Carbon NMR gives you single peaks which is great.
For carbon the value is 0-220ppm.
With NMR you have to separate the spectrum in half. One side is unsaturated and the other side is saturated.
Next class is Deducing Structure
3/6/25
COSY - H-H bond
DEPT - Carbon-Hydrogen Bond
Multiplicity of Carbons - How protons are attached to each carbon.
DEPT 45 will not show a signal for quatenary carbons
DEPT 90 will only show Methine(CH)
DEPT-135, there will be positive signals for methine and methyl carbons and negative signals for methylene carbons
2D NMR
Which protons are coupled with each other is the question?
How to interret COSY
Vicinial - separated by 2 bonds
Geminal- separated by 3 bonds
If it is separated by more then 3, the peak will show but will not be prominents. If you see a quartert in the 4 range and a triplet in the 1-2 range then you can assume that the structure is O-CH2-CH3
HECTOR( HeteroNuclear Correlation)
Carbon-Hydrogen.
Count the peaks.
What are the steps you have to follow?
Index of Hydrogen Deficiency - Formula that is required for determining how unsaturated a molecule is from its molecular formula. The IHD number is (multiple bonds + rings) and it should be a whole number. 2C+2+N-H-X divided by 2.
Analayze
Interpret the Spectrum