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27 Cards in this Set
- Front
- Back
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What is the size of the peak in NMR spectroscopy proportional to? |
It is proportional to the number of protons contributing to the absorption |
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3 main pieces of information NMR provides |
1. the chemical environments of each set of protons, 2. the number of protons within each set, 3. the number of protons in adjacent sets |
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Fundamental Equation of NMR |
∆∈p = (hγH/ 2π) Bp
h= Plank's constant , B is the magnitude of the magnetic field at the proton γ is the gyromatic ratio = 26753 radians/ gauss s |
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What physically occurs during NMR Spectroscopy? |
Molecules are situated in a magnetic field. Then they are subjected to electromagnetic radiation with energy Ep exactly equal to ∆∈p. This energy is absorbed by the protons in the +½ spin state. The absorbed energy causes these protons to flip into the -½ spin state. The amount of energy absorbed is what is studied. |
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3 formulas for radiofrequency required for absorption |
vp = Ep / h = ∆∈p / h = (γH/2π)Bp |
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Shielding |
The reduction of the local field by the circulation of nearby electrons |
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3 factors that increase the proton chemical shift |
1. Increasing electronegativity of nearby groups, 2. increasing number of nearby electronegative groups, 3. decreasing distance between the proton and nearby electronegative groups |
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Chemical shifts |
The frequency differences between 2 protons sets that have different levels of shielding |
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Chemically Equivalent |
Protons that are in the same environment. In other words, they have the same level of shielding. All protons that are chemically equivalent send 1 signal |
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What does electronegativity do to the chemical shift? |
More electronegativity results in less shilding, so the chemical shift goes up. |
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Location for chemical shift based on sp³ hybridization |
0-2 |
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Location for chemical shift based on sp² hybridization |
4.5-7 |
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Location for chemical shift based on sp hybridization |
2-3 |
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Location for chemical shift based on aromatic sp² hybridization |
7-8 |
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Chemical shift if there is a ketone |
9-10 |
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Chemical shift if there is a carboxylic acid |
10-12 |
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Coupling constant (J) |
Distance between the peaks, |
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Region of absorption for protons on a carbon next to saturated centers |
0-1.5 |
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Region of absorption for protons next to unsaturated centers (allylic, benzylic, next to carbonyl) |
1.5-2.5 |
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Region of absorption for protons next to electronegative atoms |
2.5-4.5 |
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Region of absorption for protons on double-bond carbons (vinylic protons) |
4.5-6.5 |
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Region of absorption for protons on aromatic rings (aryl protons) |
6.5-8.0 |
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What information does ¹³C NMR Spectroscopy provide? |
It determines the number of different carbon atoms in an organic molecule of unknown structure |
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What is the effect of electronegative atoms to carbon's chemical shift? |
They absorb downfield (to the left) of typical aliphatic carbons. |
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What is the general range of absorption for sp³-hybridized carbons? |
0-90 ppm |
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What is the general range of absorption for sp²-hybridized carbons? |
110-220 ppm |
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What is the general range of absorption for carbonyl carbons? |
160-220 ppm |
