NMR_HB_Part 1 - 1 Fig. 14-1, p. 544 Theory of 1H NMR H2...

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Fig. 14-1, p. 544 1
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Theory of 1H NMR H 2 molecules has two possible spin states have identical energies under normal conditions. In external magnetic field spin states have different energies. 2
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3 Background and Theory Nuclear Spin Flip +1/2 parallel to B o (lower energy); I = -1/2 antiparallel to B o (higher energy) Addition of energy results in nuclear spin flip Excited state Nuclear spin antiparallel to B o Higher energy I = +1/2 I = -1/2 Ground state Nuclear spin parallel to B o Lower energy Increasing energy Absorb energy Release energy (relaxation) E ~ 0.02 cal mol -1 = radio wave photons
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4 Background and Theory Magnetic Field Controls E E influenced by magnetic field strength at nucleus I = -1/2 I = +1/2 Spin state energy Magnetic field strength at nucleus Large magnetic field large E E Small magnetic field small E E Energy required for spin flip ( E)
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5 Background and Theory The NMR Spectrum Spectrum = plot of photon energy versus photon quantity Intensity of signal (photon quantity) Spin flip energy (photon energy) NMR signal Shielded (upfield) High magnetic field strength Deshielded (downfield) Low magnetic field strength
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6 Background and Theory The NMR Spectrum Nuclear: manipulation of nuclear spin Magnetic: magnetic field strength influences E C O C O X Resonance: tendency of a system to oscillate at maximum amplitude at a certain frequency NMR 1 H nucleus = a proton 1 H-NMR = proton NMR
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7 Background and Theory The NMR Spectrum Nuclear: manipulation of nuclear spin Magnetic: magnetic field strength influences E C O C O X Resonance: tendency of a system to oscillate at maximum amplitude at a certain frequency NMR 1 H nucleus = a proton 1 H-NMR = proton NMR
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8 Background and Theory Spectrum Structure How do we deduce structure from NMR spectrum? Information from NMR spectrum: Number of signals number of nonequivalent proton groups in molecule Position of signals (chemical shift) magnetic environment of protons
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This note was uploaded on 03/07/2011 for the course CHEM 302A taught by Professor Chellappahchanmugathas during the Winter '11 term at California State University Los Angeles .

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NMR_HB_Part 1 - 1 Fig. 14-1, p. 544 Theory of 1H NMR H2...

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