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Section 22.19 Spectroscopic Analysis of Amines

Section 22.19 Spectroscopic Analysis of Amines. H. H. N. N. R. R. H. H. symmetric. antisymmetric. Infrared Spectroscopy. The N—H stretching band appears in the range 3000-3500 cm -1 .

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Section 22.19 Spectroscopic Analysis of Amines

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  1. Section 22.19Spectroscopic Analysis of Amines

  2. H H N N R R H H symmetric antisymmetric Infrared Spectroscopy The N—H stretching band appears in the range3000-3500 cm-1. Primary amines give two peaks in this region, onefor a symmetrical stretching vibration, the other foran antisymmetrical stretch.

  3. Infrared Spectroscopy Primary amines give two N—H stretching peaks, secondary amines give one.

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

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

  6. + NH2 NH3 UV-VIS An amino group on a benzene ring shifts maxto longer wavelength. Protonation of N causesUV spectrum to resemble that of benzene. max204 nm256 nm max230 nm280 nm max203 nm254 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. •• (CH3)2NCH2CH2CH2CH3 •+ (CH3)2NCH2CH2CH2CH3 + + •CH2CH2CH3 (CH3)2N CH2 Mass Spectrometry Nitrogen stabilizes carbocations, which drives the fragmentation pathways. e–

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

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