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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)

Abstract

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.

Keywords

Lone Pair Intramolecular Hydrogen Bonding Lone Pair Electron Symmetric Mode Transition Moment 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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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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