chemical shift - inductive effects in alkanes -anisotropy -inductive effects in alkenes -δ values...
TRANSCRIPT
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Chemical shift
- Inductive effects in alkanes-Anisotropy-Inductive effects in alkenes-δ values for different groups-13C chemical shift in different groups-Solvents-Rotation
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Inductive effects in alkanes
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Inductive effect and chemical shift
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δ-values: Hybridization effects
δ values: sp3 < sp2 < sp
Carbons with sp2 hybridization hold the electrons closer to the nucelus than do sp3 carbons. This leadsto less shielding of the attached protons. Thus vinyl hydrogens have higher chemical shifts than alifatic hydrogens
Acetylenic protons (sp-hybridized C) would be expected to have a higher chemical shift than vinyl protons.
This is not true due to magnetic anistropy
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Magnetic anisotropy
A magnetic field with non-uniform density or non-sperical distribution
The presence of π-electrons in a magnetic field sets up a small, localcurrent and an anisotropic magnetic field in its close proximity
Applies only to atoms with sp2 and sp hybridization
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Inductive effects i alkenes
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Alkynes
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Chemical shift overview
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Alkaner: δ-values
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Alkener: δ values
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Benzene derivatives: δ values
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13C-Carbonyl chemical shift
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13C-cyclic compounds
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13C-Arenes
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Cyclic alkenes
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N-H and O-H chemical shift
δ: very dependent on solvent and concentration
R-O-H: 0,5 < δ < 4,5
R-N-H: 1,0 < δ < 5,0
Carboxylic acids (usually dimeric): 10 < δ 12
Enols: 12 < 18
In deuterated protic solvents: N-H, O-H and S-H can rapidly exchangeD with solvent and the 1H-NMR signal disappears.
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Solvents
Non polar solvents: Small effect on chemical shift
Polart + benzene : significant effect on chemical shift
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Slow rotation