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Introduction to NMR in Organic Chemistry: Understanding Structural Determination

Explore the principles of NMR spectroscopy for structural analysis of organic compounds, including spin characteristics, chemical shifts, and energy calculations. Learn about proton and carbon NMR spectroscopy, chemical shift values, and factors influencing signal patterns. Gain insights into the role of molecular structure in determining NMR results and discover the significance of spin-spin splitting and coupling constants. Dive into detailed information on molecular structure analysis in organic chemistry through NMR technology.

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Introduction to NMR in Organic Chemistry: Understanding Structural Determination

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  1. CHEM 344 Organic Chemistry Lab Structural Determination of Organic Compounds Lecture 2 – Intro to NMR January 22nd & 26th 2009

  2. Speed of light (c) is constant for all wavelengths • Frequency (n), the number of wavelengths per second, is inversely proportional to wavelength: n = c/l • Energy of a radiation is directly proportional to frequency E = hc/l = hn

  3. NMR Spin ½ nuclei 1H, 13C • Spin 1 nuclei2H (D), 14N Proton and Carbon NMR spectroscopy Spin 0 nuclei12C, 16O, 32S

  4. 100 E~ Radiowave 600 700 200 Nuclear Magnetic Resonance 400 400 INCREASING MAGNETIC FIELD

  5. 2.29 Chemical shift 7.04 Ha Hb 6 4 SiMe4 (TMS) Integration

  6. 3.75 Ha 6.82 Hb 6 4

  7. 1.50 Ha Downfield 9 Deshielded Upfield Hb Shielded 8.00 1

  8. 2.29 Ha 7.04 Upfield relative to Hb Shielded relative to Hb Downfield relative to Ha Deshielded relative to Ha Hb 6 4

  9. Downfield Deshielded Upfield Shielded

  10. 2.45 4.56 9 CHCl3 6

  11. 0.87 9 2.42 NH2 1.04 2 2

  12. 2.14 5.80 3 2

  13. 3.66 2.05 3 3

  14. 0.08 2.04 9 3.76 TMS 3 2

  15. Summary NMR – detailed info on molecular structure Different protons within the molecule give different signals # different protons = # signals Integration = # protons giving the signal Chemical shift value influenced by local structure of molecule (e.g. electronegative groups) Equivalent protons = same chemical shift Next time – spin-spin splitting, coupling constants…. Pages 383– 408 Solomons & Fryhle UW Edition

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