Ortho-Substituent Effects and the Fundamental NH2 Stretching Vibrations in Anilines

  • Peter J. Krueger
Conference paper
Part of the Developments in Applied Spectroscopy book series (DAIS, volume 2)


The integrated intensities, frequencies, and half-band widths of the fundamental symmetric and asymmetric NH2 stretching vibrations in 32 ortho-substituted anilines, measured in dilute carbon tetrachloride solution, were examined in relation to the corresponding absorption band parameters for 31 meta- and para-substituted anilines, taking into consideration the electronic effects of the substituents. From an almost tetrahedral configuration in p-phenylenediamine, the s-character of the nitrogen atom gradually increases as the substituent groups become more electron-withdrawing, with a resulting increase in the HNH angle and the NH force constant. Ortho-substitution in general leads to enhanced HNH angle opening, probably because of intramolecular hydrogen bonding in many cases. The decrease in half-band width for both vibrational modes in ortho-substituted anilines over corresponding values in meta- and para-compounds is ascribed to steric hindrance to solvation of the amino group.

The asymmetric intensities in ortho-substituted anilines are generally increased over corresponding values in meta- and para-compounds, unlike the behavior of the symmetric mode. These results are consistent with a vibrational mechanism taking into account the following factors for each mode: (i) the direction of the transition moment; (ii) the extent of nitrogen lone pair and aromatic п-electron participation; and (iii) the direct field effect of the ortho-substituent.


Lone Pair Intramolecular Hydrogen Bonding Lone Pair Electron Symmetric Mode Transition Moment 
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Copyright information

© Society for Applied Spectroscopy Chicago, Illinois 1963

Authors and Affiliations

  • Peter J. Krueger
    • 1
  1. 1.Department of ChemistryUniversity of AlbertaCalgaryCanada

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