Chapter 17: Aldehydes and Ketones. Nucleophilic Addition to C=O
Spectroscopic analyzis of Ketones
IR -
presence of C=O
Absorbance (cm
-1
)
Interpretation
1710-1750
C=O stretch
1
H NMR
Resonance (ppm)
Interpretation
~2.4
C
H
2
C=O (deshielding due to C=O)
~2.0
C
H
3
C=O (deshielding due to C=O)
13
C 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®p
*
(< 200
nm) n
®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.
