H Abstract Selective 1 H, 1 H decoupling Thematic use of ribavirin as an example to illustrate NMR principles and techniques 1. Williams, K. R.; King, R. W J. Chem. Educ. 1990, 67, A125-A137. UW Oshkosh Chemistry Department NSF-ILI Program (USE ) for funds to purchase the JEOL GSX-270 NMR spectrometer The molecule ribavirin serves as an excellent example for illustrating a variety of NMR principles and instrumental techniques. Ribavirin was used in a thematic fashion as a recurring example throughout a semester-long interpretative spectroscopy course. The goal was to provide a familiar molecular framework in which to introduce new concepts and techniques of increasing complexity. Proton NMR spectra were acquired at 270 MHz (carbon at 67.5 MHz) in DMSO-d 6. Unique protons & chemical shift Multiple functional groups with protons in diverse chemical environments Asymmetric structure with four contiguous stereogenic centers All protons are unique and give well-resolved 1 H NMR signals All multiplets are first order, making splitting of analysis straightforward Interesting backstory (used clinically to treat serious viral infections) Commercially available (~$40/100 mg, TCI America, Aldrich, Acros, etc.) d e f g h i j k l Ribavirin serves as a good example to illustrate spin-spin splitting, including inverted splitting tree analysis. Illustrating splitting and n+1 rule + D 2 O abcde f g hijkl H2OH2O HDO Deuterium-proton exchange Example: Irradiate proton g Splitting in coupled protons k and l affected g k/l j i f h e d d e f g h i j k l abcde f g hijkl H2OH2O 22 ° C 40 ° C 60 ° C 70 ° C 74 ° C 80 ° C b/c Coalescence Temperature = 74 °C bc A B C D E F G H ppm Proton decoupled 13 C NMR DEPT 135 CH 2 CH A/B C CH 3 CH CH 2 d e f g h ij kl d e f g h i j k l AB CD E FG H k l g f e d c b a j i h HETCOR example Conformations and 1D NOE Variable temperature NMR 13 C NMR, DEPT 2D Homonuclear NMR 1 2D Heteronuclear NMR H2OH2O a b c d e f g h i j k l H-Carbon H-Oxygen H-Nitrogen * * * * 1) Unique protons 2) Chemical shifts 3) Spin-spin splitting 4) H-D exchange 5) Selective decoupling H k dddH l dt 5.4 Hz 4.3 Hz 11.9 Hz 5.4 Hz 11.9 Hz Ribavirin illustrates how asymmetry and restricted rotation can make protons inequivalent. The aromatic ring and multiple heteroatoms also make ribavirin a good example for discussing deshielding effects and chemical shifts. Rotation about ribavirin’s amide bond can be studied at experimentally accessible temperatures. Ribavirin’s Properties Make it Useful in NMR Education Brant L. Kedrowski and William F. Wacholtz, University of Wisconsin Oshkosh, Oshkosh, Wisconsin Summary 6) NOE & conformations 7) Variable temperature NMR 8) 13 C NMR, DEPT 9) Homonuclear 2D NMR 10) Heteronuclear 2D NMR doublets triplet quartets (approximate) Ribavirin is useful in teaching the following NMR topics:Students can assign protons d-l definitively by selective decoupling. Students can assign protons b, c, and e-g as OH or NH through exchange with D 2 O. b/c e/f/g Conformations of ribavirin can be studied by NOE analysis.Homonuclear 2D techniques introduced with ribavirin. COSY example Heteronuclear 2D techniques introduced with ribavirin Carbon NMR and DEPT techniques can be introduced with ribavirin inequivalent methylene protons inequivalent amide protons Reference Acknowledgements ppm Ribavirin The effect of temperature on chemical shifts of NH and OH protons is also clearly visible (only NH and OH signals shift upfield with increasing temps)