1. Section 22.20 Spectroscopic Analysis of Amines1

2. Infrared Spectroscopy
the N—H stretching band appears in the range cm-1
primary amines give two peaks in this region, one for a symmetrical stretching vibration, the other for an antisymmetrical stretch R N H
symmetric H R N H
antisymmetric 6

3. Infrared Spectroscopy
primary amines give two N—H stretching peaks, secondary amines give one
RNH2
R2NH 6

4. compare chemical shifts in:
1H NMR
compare chemical shifts in:
H3C
CH2NH2
H3C
CH2OH
d 3.9 ppm
d 4.7 ppm N C H
is more shielded than O C H 6

5. 13C NMR
Carbons bonded to N are more shielded than those bonded to O.
CH3NH2
CH3OH
d 26.9 ppm
d 48.0 ppm

6. lmax 204 nm 256 nm lmax 230 nm 280 nm lmax 203 nm 254 nm UV-VIS
An amino group on a benzene ring shifts lmax to longer wavelength. Protonation of N causes UV spectrum to resemble that of benzene.
NH3 +
NH2
lmax
204 nm
256 nm
lmax
230 nm
280 nm
lmax
203 nm
254 nm

7. Mass Spectrometry
Compounds that contain only C, H, and O have even molecular weights. If an odd number of N atoms is present, the molecular weight is odd.
A molecular-ion peak with an odd m/z value suggests that the sample being analyzed contains N.

8. Mass Spectrometry
Nitrogen stabilizes carbocations, which drives the fragmentation pathways.
(CH3)2NCH2CH2CH2CH3 •• e–
(CH3)2NCH2CH2CH2CH3 •+
(CH3)2N
CH2 + +
•CH2CH2CH3

9. Mass Spectrometry
Nitrogen stabilizes carbocations, which drives the fragmentation pathways.
CH3NHCH2CH2CH(CH3)2 •• e–
CH3NHCH2CH2CH(CH3)2 •+
CH3NH
CH2 + +
•CH2CH(CH3)2