Chapter 20: Carboxylic Acid Derivatives

Spectroscopic Analysis of Acyl Chlorides

• IR  - presence of high frequency C=O, C-Cl too low to be useful

Absorbance (cm-1)	Interpretation
1800	C=O stretch

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

Resonance (ppm)	Interpretation
~2 - 2.5	H-C-C=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^* (~235 nm)
• πelectron 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