Chapter 20: Carboxylic Acid Derivatives
Spectroscopic analyzis of Anhydrides
IR -
presence of
two
, high frequency C=O
Absorbance (cm
-1
)
Interpretation
1820
C=O stretch
1750
C=O stretch
1
H NMR
- only the protons adjacent to the C=O are particularly characteristic.
Resonance (ppm)
Interpretation
~2 - 2.5
H
-CC=O
13
C NMR
C
=O typically 160-180 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
*
(~225nm,
diagnostic
)
p
electron from
p
of C=O
n
electron from O lone pair
p
*
antibonding C=O
Mass Spectrometry
Prominent peak corresponds to formation of acyl cations (acylium ions)
