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Chemical Detectives

Chemical Detectives. Assoc. Prof. Richard Morrison School of Chemistry Monash University (Richard.Morrison@sci.monash.edu.au). A Problem-Solving Spectral and Structural Database = a Fun and Engaging Way to Teach Spectroscopy. Uses of Chemical Detectives program:. Aids with nomenclature

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Chemical Detectives

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  1. Chemical Detectives Assoc. Prof. Richard Morrison School of Chemistry Monash University (Richard.Morrison@sci.monash.edu.au) A Problem-Solving Spectral and Structural Database = a Fun and Engaging Way to Teach Spectroscopy

  2. STAV VCE Chemistry Conference

  3. Uses of Chemical Detectives program: • Aids with nomenclature • Can choose different classes, difficulty levels • Initial spectral recognition based on known compounds • Finding unknown structures based on integrated spectral analysis STAV VCE Chemistry Conference

  4. Microanalysis • Percentage by mass of each atom in molecule STAV VCE Chemistry Conference

  5. Mass Spectrometry • Electron-impact (EI) mass spectrum • Positive ions are separated based on their mass-to-charge (m/z) ratio • One electron is removed as a result of impact • Molecular ion (M.+) – an odd-electron ion – at an even m/z if an even # of nitrogens • Fragment ions are indicative of structure, isotope peaks can also be very useful (think halogens !) • Double bond equivalents : CxHyNzOn = x-y/2+z/2+1 (rings + double bonds) STAV VCE Chemistry Conference

  6. Methyl bromide - MS STAV VCE Chemistry Conference

  7. a-cleavage STAV VCE Chemistry Conference

  8. a-cleavage STAV VCE Chemistry Conference

  9. Infrared Spectroscopy • Reveals presence of molecular functional groups by the vibrations of their bonds • Peaks beyond ‘fingerprint’ region important (> 1500 cm-1) • Presence/absence of peaks can both be useful !! • O-H bond: 3200 – 3500 cm-1 Strong and broad • N-H bond: 3100 – 3500 cm-1 Medium • C-H bond: 2850 – 3100 cm-1 Medium to strong • C=O bond: 1630 – 1800 cm-1 Strong • C=C bond: 1600 – 1680 cm-1 Weak STAV VCE Chemistry Conference

  10. IR Spectroscopy Aniline STAV VCE Chemistry Conference

  11. NMR Spectroscopy Nucleii : resonance frequencies, isotope abundances Not all nucleii are NMR active STAV VCE Chemistry Conference

  12. NMR Spectroscopy STAV VCE Chemistry Conference

  13. Nuclear Spins in a Magnetic Field • A spinning charge creates an associated magnetic field. • If a nucleus of 1H is placed in a strong external magnetic field (Bo Tesla, 1T = 104 Gauss), its magnetic moment will line up with field. • The moment can be parallel or anti-parallel to the field. STAV VCE Chemistry Conference

  14. Nuclear Spins in a Magnetic Field • For 1H and 13C, only two orientations are allowed. • Absorption of radio-frequency radiation of the appropriate energy flips the nuclear spin STAV VCE Chemistry Conference

  15. Frequency depends on Bapp m opposed to B E DE=hn m aligned with B Bapp B STAV VCE Chemistry Conference

  16. Local vs. Applied Magnetic Field m opposed to B E DE=hn m aligned with B Blocal B STAV VCE Chemistry Conference

  17. 1H NMR Spectroscopy • Three characteristics of the spectrum aid in identifying structure • Chemical shift – depends on environment (shielding/deshielding) • Integration – the number of equivalent protons determines the area under peak • Splitting pattern - identifies number of adjacent protons (more in a moment….) STAV VCE Chemistry Conference

  18. Chemical Shifts (1H NMR) STAV VCE Chemistry Conference

  19. 1H Chemical Environments 1H NMR spectrum, 100 MHz OH and NH2 protons can give broad signals due to exchange processes STAV VCE Chemistry Conference

  20. 1H NMR Spectra: Integration • Integration : the area under an NMR peak is proportional to the number of equivalent hydrogens in an environment. Integration is the proton count. STAV VCE Chemistry Conference

  21. Splitting due to an adjacent –CH group m opposed to B E m aligned with B B- B+ B STAV VCE Chemistry Conference

  22. Spin-Spin Splitting Patterns STAV VCE Chemistry Conference

  23. Multiplet Splittings and Pascal’s Triangle # of adj. H 0 1 2 3 4 5 6 7 Gives the relative integration of the multiplet signals. STAV VCE Chemistry Conference

  24. Spin-spin coupling STAV VCE Chemistry Conference

  25. 1H NMR Spectroscopy 1 2 3 1 2 3 STAV VCE Chemistry Conference

  26. 1H NMR Spectroscopy 1 2 1 1 2 STAV VCE Chemistry Conference

  27. 1H NMR Spectroscopy 1 1 1 STAV VCE Chemistry Conference

  28. 1H NMR Spectroscopy 1 1 2 1 2 STAV VCE Chemistry Conference

  29. 1H NMR Spectroscopy 1 2 3 1 3 2 STAV VCE Chemistry Conference

  30. 1H NMR Spectroscopy 1 1 2 2 3 3 2 - 4 4 STAV VCE Chemistry Conference

  31. 13C NMR Spectroscopy • Distinct peak for each C environment (13C =1.1%) • Chemical shifts:0-200 ppm vs 0-12 ppm for 1H • d depends on hybridization of C and electronegativity of attached groups • Peak areas are not indicative (a quirk of the instrumentation in pulsed FT-NMR) • Spin-spin coupling is not important : 13C-13C is unlikely due to low 13C abundance and 13C-1H coupling is removed by a technique known as “broadband decoupling” STAV VCE Chemistry Conference

  32. X C H C H C H Vinylic C C C H H X = O, N, halide Ester/Amide/ Aldehyde/ Ketone/ Carboxylic Acid Saturated C-H Unsat. C-H Aromatic 240 200 160 120 100 60 40 0 Chemical shift () 13C NMR Spectra : Chemical Environments Chemical shift related to the BL which is determined by the hybridization of the carbon centre and the groups attached. STAV VCE Chemistry Conference

  33. 13C NMR Spectroscopy Aromatic C - H STAV VCE Chemistry Conference

  34. 13C NMR Spectroscopy 1 2 3 3 1 2 Carboxylic acid C (Quaternary C) Aliphatic C STAV VCE Chemistry Conference

  35. 13C NMR Spectroscopy 2 1 2 3 3 1 Aldehyde C Aliphatic C STAV VCE Chemistry Conference

  36. 13C NMR Spectroscopy 1 2 3 4 1 3 2 4 Aliphatic C STAV VCE Chemistry Conference

  37. 13C NMR Spectroscopy 4 5 5 1 4 2 3 3 2 1 Carbonyl C (quaternary C) Aliphatic C Quaternary C STAV VCE Chemistry Conference

  38. 13C NMR Spectroscopy 2 1 2 1 Alkene C Alkane C STAV VCE Chemistry Conference

  39. STAV VCE Chemistry Conference

  40. Packages / Applications STAV VCE Chemistry Conference

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