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Chemical Shift

Chemical Shift. Carbon-13 Spectra. How many C-13 signals? Which signals are further upfield ? Can the compounds be differentiated?. Correlation Chart. Same number of signals Occur in different areas of spectrum Predictable shifts. Chemical Shift Tables. Complex vs simple Basics:

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Chemical Shift

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  1. Chemical Shift

  2. Carbon-13 Spectra • How many C-13 signals? • Which signals are further upfield? • Can the compounds be differentiated?

  3. Correlation Chart • Same number of signals • Occur in different areas of spectrum • Predictable shifts

  4. Chemical Shift Tables • Complex vs simple • Basics: • Alkane: 5-45ppm • C-Q: 40-70ppm • sp: 70-100ppm • sp2: 100-160 ppm • Carbonyl: 160-220 ppm

  5. Predict C-13 Chemical Shifts • If carbon fits two categories, choose higher shift

  6. More subtle points • Inductive effects • Additive effects • More substituted sp3 carbon is further downfield

  7. More subtle points • Carbonyls • Above 200ppm, ketone and aldehyde • Below 200ppm, O=C-Q • Explain by shielding and resonance

  8. More subtle points • Alkene vs Alkyne

  9. Which Structure(s) Fit? TMS absent CDCl3

  10. Which Structure Fits?

  11. C3H8O

  12. Proton NMR Shifts

  13. Basic Correlation Chart • How many 1H signals? • Shift?

  14. Common “exceptions” • Phenyl protons give one “signal” even if nonequivalent

  15. Common “exceptions” • Exchangeable protons are broad and small • Washed away with D2O

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