Chapter 15: Alcohols, Diols and Thiols

Spectroscopic analyzis of Alcohols

• IR  - presence of -OH.

 

Absorbance (cm-1)	Interpretation
3200 - 3650  (broad)	O-H stretch
1200 -1250	C-O stretch

• ¹H NMR - H- C-OH unit are the most easily recognised.

 

Resonance (ppm)	Interpretation
0.5 - 5 (broad, exchangeable)	-OH proton
3.3 - 4.0	H-C-O (deshielding due to O)


 
• ¹³C NMR

C-OH typically 60 - 75 ppm (deshielding due to O)

•   UV-VIS

Simple alcohols give usually no absorption above 200 nm.
 
• Mass Spectrometry

Molecular ion, M⁺, is usually small, loss of H₂O (M - 18) is often apparent.
Loss of alkyl radicals due to cleavage of branches adjacent to C-OH is common.