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10 Cards in this Set
- Front
- Back
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Chemical shift
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Used the delta scale and has the units ppm
Is the difference between the chemical shift of the sample in comparison of a standard TMS absorption |
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Factor affecting chemical shift
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Proximity to an electronegative atom
Proximity to Pi electrons Anisotropic effects - localised magnetic field from the circulating electrons of at atom - either paramagnetic or dimagnetic |
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Electronegative atoms _____ the nucleus because ____________
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deshield
draw electron density away from an atom |
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Anisotropic effects are
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localised magnetic field from the circulating electrons of at atom - either paramagnetic or dimagnetic
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Circulating electrons _____________ the nucleus because ______________
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shield
spin around the nucleus divert some of the energy |
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Pi electrons can ___________ or ____________ depending on _______________
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shield
deshield whether lines of force (magnetic moment) is parallel or antiparallel |
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Parallel magnetic moment
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deshield
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Antiparallel magnetic moment
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shield
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Deshielding moves chemical shift
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downfield
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NMR splitting - spin/spin coupling
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Nuclei possess a small magnetic field which if less than 3 bonds away can be experienced by another proton
This is known as spin-spin coupling and results in NMR splitting pattern Splitting results in two spin states - +1/2 alpha -1/2 beta These are slightly different in energy when a field is applied - shielding also affects the nuclei chemical environment Results in a nuclei having a different split depending on environment of neighbouring H1 resulting in complex signals |
