NMR-2 Chemical Shift - NMR Chemical Shifts Further...

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NMR Chemical Shifts Further Discussion
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Typical 1 H Chemical Shift Ranges
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Why Different Chemical Shifts Are Observed? Shielding by bonding electrons Magnetic anisotropy
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Shielding by Bonding Electrons B 0 B i B T < B 0 because of B i B α β B 0 B T Δ E Electron density B i B T Resonates at smaller ν γ B T 2 π ν = B T = B 0 (1 - σ ), σ : shielding constant
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1-Chloro-2,2-dimethylpropane 0 1 2 3 4 PPM CH 2 C CH 3 CH 3 CH 3 Cl Electronegative element Less shielded More shielded
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Shielding and Electronegative Elements CH 3 -F CH 3 -Cl CH 3 -Br CH 3 -I CH 3 -H δ (CH 3 ) 4.13 2.84 2.45 1.98 0.13 Electronegativity 4.0 3.0 2.8 1.98 2.1
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Aromatic Protons H H H H + 1/7 electron withdrawing H - 1/5 electron donating δ (ppm) 9.17 7.27 5.37
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Beyond Shielding C C H H H H H H C C H H H H C C H H δ (ppm) 0.9 5.25 1.80 H H H 7.2ppm 9.3ppm - 3.0ppm !! sp3 sp2 sp More s-charactor (more electronegative carbon)
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Magnetic Anisotropy A H B 0 B i A B i H When B i B i = magnetically isotropic When B i B i = magnetically anisotropic Decreased B T Increased B T
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Benzene Ring H B 0 B i B i H B i B i << Benzene protons are deshielded , and show up at more down field positions than vinylic protons. deshielded shielded H H 9.3ppm deshielded -3.0ppm shielded
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Other Benzene Derivatives H H ~ 7ppm - 0.51 ppm CH 3 CH 3 H ~ 8 ppm CH 3 : - 4.25 ppm
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Cyclophane 0 1 2 3 4 5 6 7 8 PPM CH 2 CH 2 CH 2 CH 2 CH 2 2.63 1.55 1.08 0.70 0.51 ChemDraw says Softwares are useful, but don’t trust them too much.
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Alkynes C C + - - + H H H ~ 2ppm ~ 7ppm ~ 9ppm shielded shielded deshielded deshielded
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Alkenes + - - + C C H H 1.42 ppm - 0.42 ppm H H 1.44 ppm 2.82 ppm H OH 3.53 ppm HO H 3.75 ppm
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Alkanes + - - + O OH H H HO OH H H HO O CH 3 H O OH H H HO OH H H HO H O CH 3 5.18 ppm 4.69 ppm 3.78 ppm 3.97 ppm
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Typical 1 H Chemical Shift Ranges R-CO 2 H : 10 ~ 14 ppm R-N H - and R-O H : 0.5 ~ 7.5 ppm R-S H : 1 ~ 2 ppm
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NMR-2 Chemical Shift - NMR Chemical Shifts Further...

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