1 / 19

Chem-805/806

Chem-805/806. Structure determination. Strategies to assign resonances. Entry point: Try to find all the resonances that can be assign without ambiguity from 1D-NMR Predict chemical shifts (H and C) and compare with observed shifts.

dung
Télécharger la présentation

Chem-805/806

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chem-805/806 Structure determination

  2. Strategies to assign resonances • Entry point: Try to find all the resonances that can be assign without ambiguity from 1D-NMR • Predict chemical shifts (H and C) and compare with observed shifts. • Integration can be used to match number of protons in overlapping multiplets • Predict multiplets and see how they match

  3. Bookkeeping • Determine which signals belong to CH, CH2 and CH3. Integrate H-NMR • Create tables of proton and carbon shifts related to each other • Try to understand the shift (which type of oxygen do you have (carbonyl, ester, ether..) • Build substructure that make sense of multiplicity. • Propose a structure. Number the structure (UPAC rules). Assign H and C NMR.

  4. Example : H-NMRC8H15NO2 3H 2H + 1H 2H 1H 1H 1H 1H 1H 1H 1H

  5. C8H15NO2 Example COSY 3H, t 2H, q CH3 - CH2 - O

  6. C8H15NO2 Example HMQC CH2 CH2 CH2 CH2 O-CH2 CH3 CH  OH? NH?        

  7. Example : H-NMRC8H15NO2 In C13 NMR: 170 ppm ester 3H (CH3-CH2-O-C=O) 2H + 1H 2H OH or NH 1H 1H 1H 1H 1H 1H 1H         

  8. C8H15NO2 Example COSY 3H, t CH3-CH2-O-CO- NH 2H, q            All atoms are accounted for CH2   CH2   CH CH2 CH2 NH     Deshielded by N

  9. Example Jeffrey H. Simpson, “Orgamic structure determination using 2-D NMR spectroscopy”

  10. Example : H-NMRC8H15NO2      3H 2H + 1H 2H 5 NH 6’ 4’ 2’ 3 6 5’ 2 4

  11. Example

  12. Assignment of quaternary Carbons Quaternary carbons: 176.3, 154.8, 143.4, 125.2, 120.4 C4 = 176 C10 = 155, most deshielded due to oxygen C11 C10 C4

  13. HMBC 2 12 13 6 3 10 4 13 12 5 7 2 11

  14. Strategy for Unknown molecules • Consider solvent used: contribution to H and C NMR • Inspect H and C spectra for obvious clues Deshielded HOD Aromatic Solvent: D2O CHO

  15. EXPANSIONS CH – O Aromatic Ortho CHO

  16. C13 O CH-O Aromatic CH O 193.3 ppm CH=O Not shown

  17. Unknown: HMQC • CHO group: 10.2 ppm – 193.3 • 4 aromatic H: disubst., Ortho (2D, 2T) • Deshielded H at 5.2, coupled to C 100.1 ppm : deshielded by 2 O? CH-O O CH O Ortho aromatic CHO

  18. Unknown: HMQC expansion CHO CH2-O 4 x CH-O

  19. Unknown : good accounting

More Related