Section 22.20 Spectroscopic Analysis of Amines 1

Infrared Spectroscopy the N—H stretching band appears in the range 3000-3500 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

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

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

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

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

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.

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

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