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1 H NMR Interpretation: A New Tool for Students

Learn why NMR interpretation is essential for molecular identification, improves problem-solving skills, and how the NMR Mosaic tool simplifies complex multiplets. Explore the process and common errors in NMR interpretation to enhance your understanding.

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1 H NMR Interpretation: A New Tool for Students

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  1. 1H NMR Interpretation: A New Tool for Students John V. McClusky Texas Lutheran University Texas Lutheran University

  2. Why Teach NMR Interpretation? • Necessary for molecular identification • Important for teaching problem solving skills • Complex and abstract • Must concentrate on details and big picture • “You guess, you loose” Texas Lutheran University

  3. The Process • Students must use • Integration • Number of hydrogens making the peak • Multiplicity • Number of adjacent hydrogens • Chemical shift • Functional groups • Determine the molecular structure Texas Lutheran University

  4. The Problem Doesn’t look like Texas Lutheran University

  5. Typical Student Errors • Ignore integration, multiplicity, or chemical shift • Interpret multiplicity incorrectly • n+1, n, or n-1? • Switch integration and multiplicity • Force spectrum to “match” preconceived molecule Texas Lutheran University

  6. NMR Mosaic Goals • Make NMR Interpretation more concrete • Reinforce need to use all data • Chemical shift • Multiplicity • Integration • Visualize relationship between multiplicity and connectivity • Retain all problem-solving aspects Texas Lutheran University

  7. NMR Mosaic Spectral peaks Molecular fragments Molecule fit mismatch Finished Revise -- Texas Lutheran University

  8. Strengths of the NMR Mosaic • Requires use of integration, chemical shift, and multiplicity • Accentuates interpretation errors • Eases interpretation of complex multiplets • Illustrates relationship between connectivity and multiplicity Helps students understand and visualize NMR interpretation Texas Lutheran University

  9. H | ─C─ | H H | ─C─ | H Funct. Grp. CH3 Mosaic Pieces Peak is from Splitting indicates Chemical shift Final mosaic piece a CH2 adjacent CH3 indicates adjacent functional group + + = Funct. Grp CH3 Students add static clings to generic pieces to produce a custom piece encoding connectivity and functionality Texas Lutheran University

  10. Example: C3H7Cl Texas Lutheran University

  11. H | ─C─ | H Example: C3H7Cl Texas Lutheran University

  12. CH2 H | ─C─ | H Example: C3H7Cl Texas Lutheran University

  13. CH2 Funct. Grp. H | ─C─ | H Example: C3H7Cl Texas Lutheran University

  14. CH2 Funct. Grp. H | ─C─ | H Example: C3H7Cl X- Texas Lutheran University

  15. H | ─C─ | H CH2 CH3 CH2 Funct. Grp. H | ─C─ | H Example: C3H7Cl X- Texas Lutheran University

  16. H | ─C─ | H CH2 CH3 CH2 Funct. Grp. H | ─C─ | H H | H─C─ | H CH2 Example: C3H7Cl X- Texas Lutheran University

  17. H | ─C─ | H CH2 H | ─C─ | H Funct. Grp. CH3 CH2 H | H─C─ | H CH2 Example: C3H7Cl X- 1-chloropropane Texas Lutheran University

  18. NMR Mosaic Simplifies Interpretation of Complex Multiplets • Adjoining pieces specify connectivity • Interpretation is no longer “impossible” Texas Lutheran University

  19. Example: C4H9Cl Texas Lutheran University

  20. CH2 H | ─C─ | Funct. Grp. CH3 Example: C4H9Cl X- Texas Lutheran University

  21. H | ─C─ | H CH2 H | ─C─ | Funct. Grp. CH3 Example: C4H9Cl X- Undetermined Splitting Texas Lutheran University

  22. H | ─C─ | H CH2 H | H─C─ | H H | ─C─ | CH Funct. Grp. CH3 Example: C4H9Cl X- Undetermined Splitting Texas Lutheran University

  23. H | ─C─ | H CH2 H | H─C─ | H H | ─C─ | CH Funct. Grp. CH3 H | H─C─ | H CH2 Example: C4H9Cl X- Undetermined Splitting Texas Lutheran University

  24. H | ─C─ | H CH2 H | H─C─ | H H | ─C─ | CH Funct. Grp. CH3 H | H─C─ | H CH2 Example: C4H9Cl X- Undetermined Splitting Texas Lutheran University

  25. CH2 H | H─C─ | H H | ─C─ | CH Funct. Grp. H | ─C─ | H CH CH3 CH3 H | H─C─ | H CH2 Example: C4H9Cl 2-chlorobutane X- Texas Lutheran University

  26. NMR Mosaic Helps Students Catch Mistakes • Mosaic pieces no longer match • Focus students on incorrectly interpreted peaks Texas Lutheran University

  27. Example: C3H7Cl Texas Lutheran University

  28. H | ─C─ | H Funct. Grp. CH2 H | ─C─ | H CH3 CH3 H | H─C─ | H CH2 Example: C3H7Cl X- Incorrect Match ↑ Texas Lutheran University

  29. H | ─C─ | H CH2 H | ─C─ | H Funct. Grp. CH3 CH2 H | H─C─ | H CH2 Example: C3H7Cl X- Corrected Piece Matches Texas Lutheran University

  30. Computer Version • Same basic format as “hardware” version • Extensive help section • Over 50 problems, many including Infrared, 13C NMR, and reaction sequences • Student answers to problems are checked for correctness Texas Lutheran University

  31. Main Program Work Area Texas Lutheran University

  32. Texas Lutheran University

  33. Student Experiences • Students found the NMR Mosaic a great aid in NMR Interpretation • Much higher percentage of students successfully solved problems • Allows much more realistic problems on exams • Better students weaned themselves off NMR Mosaic • Students had a much stronger understanding of NMR interpretation Texas Lutheran University

  34. NMR Mosaic: Key Features • Requires use of Integration, Multiplicity, and Chemical Shift • Accentuates students’ interpretation errors • Eases interpretation of complex multiplets • Reinforces relationship between multiplicity and connectivity • Can be used with thousands of spectra EMPHASIZES UNDERSTANDING AND PROBLEM SOLVING SKILLS Texas Lutheran University

  35. Acknowledgement Texas Lutheran University www.tlu.edu/nmr Texas Lutheran University

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