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chap13 - NMR CHAP 13 NMR nuclear magnetic resonnance...

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1 NMR CHAP 13 NMR- nuclear magnetic resonnance Advantages- 1. small sample. 2. Non-destructive (sometimes slightly acidic) 3. Detailed structural information Used to study nuclei with odd atomic spin numbers (1/2) which means odd mass numbers and odd atomic numbers. Ex. 1 H, 13 C (isotope), 15 N (isotope), 19 F, 31 P Treat a proton as a rotating sphere, movement of charge generates a magnetic field. Like a canoe in a river, the magnetic field is equivalent to the current N S S N low energy state a -spin state N S S N high energy state b -spin state
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2 D E = g hH o /2 P H o = strength of magnet g = gyromagnetic rotation depends on nucleus D E = 1 x 10 -5 kcal/mol Resonance occurs when the proton flips its spin, goes from alpha to beta spin state by being irradiated with radio frequency photons. Resonance frequency is equal to u = 1/2 P g H o Dependent on magnetic field. Old days used CW (continous wave) NMR Now use FT-NMR- uses short microsecond rf pulses applied along the x-axis and provides the entire frequency range, hits all protons simultaneosely.
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