Chapter 20: Carboxylic Acid Derivatives

Spectroscopic Analysis of Esters

• IR  - presence of C=O, and two C-O bands (Csp²-O and Csp³-O bonds)

Absorbance (cm-1)	Interpretation
1735	C=O stretch
1300-1000	two bands for C-O stretch

• ¹H NMR - deshielded proton of H-C-O is often recognisable, and H-C-C=O.

Resonance (ppm)	Interpretation
3.5-4.5	H-COC
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^* (~207 nm)
• 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