Chapter 20: Carboxylic Acid Derivatives

Spectroscopic Analysis of Amides

• IR  - presence of low frequency C=O, N-H stretches for 1^o or 2^o amides.

Absorbance (cm-1)	Interpretation
1660	C=O stretch
3500 and 3100	N-H stretch (two for NH2, one for NH)

• ¹H NMR - N-H protons often broad,

Resonance (ppm)	Interpretation
5-8  (broad, exchangeable)	NH
~ 2 - 2.4	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

absorption maxima n→ π^* (~215 nm)
• n electron from O lone pair
• π^* antibonding C=O

• Mass Spectrometry

Molecular ion M+ often visible.
A prominent peak corresponds to formation of acyl cations (acylium ions)


 

© Dr. Ian Hunt, Department of Chemistry