Review of Spectroscopic Methods II

Review of Spectroscopic Methods II - Quick Review of...

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Quick Review of Spectroscopic Methods II. Overview of IR and NMR.
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Nuclear Magnetic Resonance: NMR Whereas IR responds to the molecular vibrations of bond stretching, twisting, and scissoring, NMR responds to the presence of the nucleus under observation. Usually, the observational nucleus is 1 H, but other nuclei such as 13 C, 31 P, 19 F, or 15 N may be targeted.
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Signal Sensitivity (Response) The sensitivity or response strength for a specific nuclei depends upon several factors. Natural abundance of the nuclei. Strength of the magnetic field ( B ) used. The magnitude of the gyromagnetic constant ( γ ) for the nuclei.
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Natural Abundance: All else being equal, different nuclei would have similar responses or sensitivities. However, for some elements, like carbon, the NMR active isotope is a minor component. C: 98.9% 12 C (inactive) & 1.1% 13 C (active) So the signal for 13 C is only ~1% as strong as the signal for 1 H.
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Magnetic Field B: Normally the spin (NMR) active nuclei are randomly oriented in space. But, in a magnetic field ( B ), the spin active nuclei orient themselves into two groups; those oriented with the field and those oriented against the field.
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Magnetic Field Strength B . B=0 Random B increases ∆Ε ∆Ε220d B=0 Random B increases ∆Ε ∆Ε220d
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Magnetic Field B .
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