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Solving Unknown Structures Using NMR

Solving Unknown Structures Using NMR. Organic Structure Analysis, Crews, Rodriguez and Jaspars. Six Simple Steps for Successful Structure Solution. Get molecular formula. Use combustion analysis, mass spectrum and/or 13 C NMR spectrum. Calculate double bond equivalents.

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Solving Unknown Structures Using NMR

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  1. Solving Unknown Structures Using NMR Organic Structure Analysis, Crews, Rodriguez and Jaspars

  2. Six Simple Steps for Successful Structure Solution • Get molecular formula. Use combustion analysis, mass spectrum and/or 13C NMR spectrum. Calculate double bond equivalents. • Determine functional groups from IR, 1H and 13C NMR • Compare 1H integrals to number of H’s in the MF. • Determine coupling constants (J’s) for all multiplets. • Use information from 3. and 4. to construct spin systems (substructures) • Assemble substructures in all possible ways, taking account of dbe and functional groups. Make sure the integrals and coupling patterns agree with the proposed structure.  SOLUTION Organic Structure Analysis, Crews, Rodriguez and Jaspars

  3. USING 1H NMR DATA UNKNOWN B • A compound shows an M+. in the EIMS at 154 m/z • Further fragments are at 121, 93, 71, 55 and 39 m/z • The IR shows bands at 3400 cm-1 (broad) & 1450 cm-1 • Use the 1H and 13C data to determine the structure of the • compound Organic Structure Analysis, Crews, Rodriguez and Jaspars

  4. 13C NMR DATA UNKNOWN B t t t q q d d q s s A B C D E F GHI J Organic Structure Analysis, Crews, Rodriguez and Jaspars

  5. MOLECULAR FORMULA DETERMINATION UNKNOWN B s d t q A C D F I G H J B E (C)2 + (CH)2 + (CH2)3 + (CH3)3 = C10H17 = 137 Da The M+. appears at 154 m/z, so there is a mass difference of 17 Da (= OH) Therefore molecular formula = C10H18O (2 dbe) Organic Structure Analysis, Crews, Rodriguez and Jaspars

  6. 1H NMR DATA UNKNOWN B Integrals: ONLY 17 H! 5H 3H 3H 3H 2H H Organic Structure Analysis, Crews, Rodriguez and Jaspars

  7. SUBSTRUCTURES UNKNOWN B dC 112 t, 146 d dH 5.00 dd, 5.15 dd, 5.85 dd dC 125 d, 132 s dH 5.05 t & Me groups at dH 1.5 dC 73 s dH 1.05 s MF = C10H18O ! Organic Structure Analysis, Crews, Rodriguez and Jaspars

  8. WORKING STRUCTURES UNKNOWN B A – Ha should be ddt B – Ha should be ddt C – Ha should be dd Organic Structure Analysis, Crews, Rodriguez and Jaspars

  9. MASS SPECTRAL FRAGMENTATION UNKNOWN B Fragments at: 121, 93, 71, 55 and 39 m/z Organic Structure Analysis, Crews, Rodriguez and Jaspars

  10. USING MASS SPECTRAL DATA UNKNOWN G • A compound shows an M+. in the EIMS at 128 m/z • Further fragments are at 99, 83, 72 and 57 m/z • The IR shows bands at 1680 cm-1 (strong) & • bands at 1400 - 1500 cm-1 • Use the 1H and 13C NMR and MS data to determine • the structure of the compound Organic Structure Analysis, Crews, Rodriguez and Jaspars

  11. 13C NMR DATA UNKNOWN G t t q d d d t A B C D E FG Organic Structure Analysis, Crews, Rodriguez and Jaspars

  12. MOLECULAR FORMULA DETERMINATION UNKNOWN G s d t q A B C D E F G (C)0 + (CH)3 + (CH2)3 + (CH3)1 = C7H12 = 96 Da The M+. appears at 128 m/z, so there is a mass difference of 32 Da (= O2) Therefore molecular formula = C7H12O2 (2 dbe) Organic Structure Analysis, Crews, Rodriguez and Jaspars

  13. 1H NMR DATA UNKNOWN G Integrals: 12 H Total 3H 2H H H H H H H H Organic Structure Analysis, Crews, Rodriguez and Jaspars

  14. SUBSTRUCTURES UNKNOWN G dC 96 d dH 4.9 t dC 140 d, 101 d dH 6.15 d, 4.70 m dC 64 t 4 Oxygens in substructures but only 2 in MF MF = C7H12O2 ! Organic Structure Analysis, Crews, Rodriguez and Jaspars

  15. WORKING STRUCTURES UNKNOWN G 13C Shift additivity data MS Fragmentation Retro Diels-Alder Fragments are at 99, 83, 72 and 57 m/z Organic Structure Analysis, Crews, Rodriguez and Jaspars

  16. USING COSY DATA UNKNOWN H • A compound shows an [M + H]+ in the FAB MS at 132 m/z • MW = 131 (Odd) therefore odd number of nitrogens • A further fragment is at 86 m/z • The IR shows bands at 3400cm-1 (broad) & 1640 cm-1 (broad) • Use the NMR data to determine the structure of the compound Organic Structure Analysis, Crews, Rodriguez and Jaspars

  17. 13C NMR DATA UNKNOWN H d t t d s A B C D E Organic Structure Analysis, Crews, Rodriguez and Jaspars

  18. MOLECULAR FORMULA DETERMINATION UNKNOWN H s d t q B C D E A (C)1 + (CH)2 + (CH2)2 + (CH3)0 = C5H6 = 66 Da The MW is 131, so there is a mass difference of 65 Da (= NO3H3) Therefore molecular formula = C6H9NO3 (2 dbe) Organic Structure Analysis, Crews, Rodriguez and Jaspars

  19. 1H NMR DATA UNKNOWN H Integrals: D2O so no XH (OH, NH) ONLY 6 H! H H H H 2H b c d d’ e e’ Organic Structure Analysis, Crews, Rodriguez and Jaspars

  20. SUBSTRUCTURES UNKNOWN H dC 176 s IR band at 3400 dC 70 d dH 4.6 m dC 60 d dH 3.9 m MF = C5H9NO3 ! Organic Structure Analysis, Crews, Rodriguez and Jaspars

  21. 1H – 1H COSY NMR SPECTRUM UNKNOWN H b c d d’ e e’ d-e’ c-e/e’ e-e’ b-e/e’ b-d/d’ d-d’ Organic Structure Analysis, Crews, Rodriguez and Jaspars

  22. 1H – 1H COSY NMR DATA UNKNOWN H c-e/e’ b-e/e’ b-d/d’ Also 4-bond correlation d-e’ Diastereotopic pairs d-d’ and e-e’ Organic Structure Analysis, Crews, Rodriguez and Jaspars

  23. SUBTRUCTURES UNKNOWN H MF = C5H9NO3 Working structures: Organic Structure Analysis, Crews, Rodriguez and Jaspars

  24. ASSIGNING NMR DATA TO A KNOWN STRUCTURE GUAIAZULENE Expect: (C)5 (CH)6 (CH2)0 (CH3)4 MF = C15H18 Organic Structure Analysis, Crews, Rodriguez and Jaspars

  25. 13C NMR DATA GUAIAZULENE (C)5 + (CH)6 + (CH2)0 + (CH3)4 = C15H18 qq LM d J d H d K ddd EFG q N q O s B s D s I s A s C Organic Structure Analysis, Crews, Rodriguez and Jaspars

  26. HSQCNMR DATA GUAIAZULENE n o lm k O O N LM N LM K K Organic Structure Analysis, Crews, Rodriguez and Jaspars

  27. HSQCNMR DATA GUAIAZULENE g e f h j J J H H G G F F E E Organic Structure Analysis, Crews, Rodriguez and Jaspars

  28. 1HNMR DATA GUAIAZULENE Label spectrum according to HSQC: 3H m 3H l 3H o 3H n H g H e H f H j H h H k Organic Structure Analysis, Crews, Rodriguez and Jaspars

  29. HMBC NMR DATA GUAIAZULENE We will need expansions: Organic Structure Analysis, Crews, Rodriguez and Jaspars

  30. HMBC NMR DATA GUAIAZULENE g e f j h HI G F CDE B A I-g I-j G-f F-g C-h D-j D-e C-g B-h A-f Organic Structure Analysis, Crews, Rodriguez and Jaspars

  31. HMBC NMR DATA GUAIAZULENE g e f j h O N LM K N-h K-g K-f Organic Structure Analysis, Crews, Rodriguez and Jaspars

  32. HMBC NMR DATA GUAIAZULENE n o lm LM-lm K-lm H-n I-o C-n D-o B-lm A-n Organic Structure Analysis, Crews, Rodriguez and Jaspars

  33. HMBC NMR DATA GUAIAZULENE ‘Obvious’ assignments: N/O F/H J/E H/F E/J M O/N K L 1H-1H COSY data indicates that e and j are adjacent (J(e-j) = 4 Hz) as are f and h (J(f-h) = 11 Hz) Organic Structure Analysis, Crews, Rodriguez and Jaspars

  34. HMBC NMR DATA GUAIAZULENE N/O H J/E F E/J G M O/N K L Signal for f is a dd long-range coupling to remaining proton g Organic Structure Analysis, Crews, Rodriguez and Jaspars

  35. HMBC NMR DATA GUAIAZULENE N A H J/E C F E/J B G M O K L HMBC data can’t decide positions of E, J HMBC data can’t decide positions of D, I How do we decide? Organic Structure Analysis, Crews, Rodriguez and Jaspars

  36. FINALISING THE ASSIGNMENTS GUAIAZULENE NOE N A H J C F E I D B G M O K L puts it in a similar environment to C (136 ppm) Placing D (134 ppm) here This puts I (125 ppm) here Organic Structure Analysis, Crews, Rodriguez and Jaspars

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