Chapter 22: Amines

Spectroscopic Analysis

• IR - The -N-H should be apparent. -NH one band, -NH₂ two bands (symmetric and asymmetric stretches)

Absorbance (cm-1)	Interpretation
3500 - 3100	NH stretch
1350 - 1000	C-N stretch

• ¹H NMR - The -N-H proton(s) tend to be broad peaks. N is less electronegative than O so it deshields less (i.e. lower chemical shift)

Resonance (ppm)	Interpretation
0.5 - 5.0 (broad, exchangeable)	-NH proton
1.5 - 3.0	CH2-NR2

• ¹³C NMR

C-N typically 35 - 50 ppm (deshielding due to N)
note: the deshielding is less than that observed in alcohols, C-O = 50 - 65 ppm)
 
• UV-VIS

 maxima due to  n→σ* (190 nm)
• n electron from N lone pair
• σ* antibonding C-N

 
• Mass Spectrometry

Peak for the molecular ion, M⁺, is usually apparent.
The nitrogen rule : compounds composed of only C, H, O have an even molecular weight.
If a compound contains an odd number of N atoms will have an odd molecular weight. (the Nitrogen rule).
Since N is very good at stabilising positive charge, cleavage at the b-carbon are common.

© Dr. Ian Hunt, Department of Chemistry