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1 H NMR Interpretation: A New Tool for Students

1 H NMR Interpretation: A New Tool for Students. John V. McClusky Texas Lutheran University. Why Teach NMR Interpretation?. Necessary for molecular identification Important for teaching problem solving skills Complex and abstract Must concentrate on details and big picture

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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 peak incorrectly • n+1 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. Advantages of the NMR Mosaic • Requires use of integration, chemical shift, and multiplicity • Accentuates student’s 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 H | ─C─ | H Funct. Grp. CH3 CH2 Example: C3H7Cl X- Texas Lutheran University

  16. H | ─C─ | H CH2 H | ─C─ | H Funct. Grp. CH3 CH2 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. Functional Groups • Easily used for spectra with over 10 carbons plus aromatic rings • All major functional groups including: • Aromatic rings (mono and di-substituted) • Alcohols, ethers, esters, aldehydes, ketones, carboxylic acids, amines …… • Alkenes Texas Lutheran University

  31. 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 and only used it when had problems • Students had a much stronger understanding of NMR interpretation Texas Lutheran University

  32. 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

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