Chapter 17: Aldehydes and Ketones. Nucleophilic Addition to C=O

Spectroscopic Analysis of Ketones

• IR  - presence of  C=O

Absorbance (cm-1)	Interpretation
1710-1750	C=O stretch

• ¹H NMR

Resonance (ppm)	Interpretation
~2.4	CH2C=O (deshielding due to C=O)
~2.0	CH3C=O  (deshielding due to C=O)


 
• ¹³C NMR

C=O typically 190-220 ppm (deshielding due to O)
• minimal intensity, characteristic of C's with no attached H's

•   UV-VIS

two absorption maxima p to p^* (< 200 nm) n to p^* (> 200 nm)
• p electron from p of C=O
• n electron from O lone pair
• p^* antibonding C=O
  
  
• Mass Spectrometry

Molecular ion, M⁺, is prominent.
Loss of alkyl radical leads to the formation of acyl cations (acylium ions), e.g.

© Dr. Ian Hunt, Department of Chemistry