L39 - Non-First Order Coupling/Carbon NMR

• When will protons not couple to each other?

  Chemically equivalent protons won't couple to each other. Think about symmetry!

  
• What kind of coupling happens in aromatic rings?

  Ortho, meta and para couplings.

  
• What does size of coupling depends on?

  Orientation of protons to each other.

  
• What's the equation used to predict chemical shift?

  Chemical shift = 7.27 + (Zortho + Zmeta)

  
• What does a 13C NMR spectra look like?

  - Aromatic carbons typically 120-160ppm.

  
  

  - Long relaxation times (excited to ground state) so no integrations.

  
  

  - Peaks are decoupled and give single lines.

  
  

  - Quaternary carbons appear shorter.
• What are the most significant factors affecting 13C chemical shifts?

  - Electronegativity of groups attached to C atoms.

  
  

  - Hybridisation of carbon (sp2/sp3).

  
• At what ppm would we typically see Aromatics on 13C spectra?

  120-160ppm.

  
• At what ppm would we typically see C=O carbonyls on 13C spectra?

  200-220ppm

  
• At what ppm would we typically see O=C-X on a 13C spectra?

  150-190ppm.

  
• At what ppm would we typically see C=C bonds on a 13C NMR spectra?

  100-150ppm.

  
• At what ppm would we typically see C-X bonds on 13C NMR?

  40-80ppm.

  
• At what ppm do we typically see C-C bonds on a 13C NMR spectra?

  0-50ppm.

  
• What does the no. of signals show on a 13C NMR spectra?

  The amount of carbonenvironments.Not total C no!
• What does DEPT 90 show?

  DEPT 90 only shows carbons with 1x H attached (CH).

  
• What does DEPT 135 show?

  DEPT 135 shows CH and CH3 as positive peaks, and CH2 as negative peaks.