Chapter 20: Carboxylic Acid Derivatives

Spectroscopic Analysis of Anhydrides

• IR  - presence of two, high frequency C=O

Absorbance (cm-1)	Interpretation
1820	C=O stretch
1750	C=O stretch

• ¹H NMR - only the protons adjacent to the C=O are particularly characteristic.

Resonance (ppm)	Interpretation
~2 - 2.5	H-CC=O


 
• ¹³C 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 π→ π^* (<200 nm) n→ π^* (~225nm, diagnostic)
• π electron from π of C=O
• n electron from O lone pair
• π^* antibonding C=O

• Mass Spectrometry

Prominent peak corresponds to formation of acyl cations (acylium ions)

© Dr. Ian Hunt, Department of Chemistry