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Structural Chemistry

, Volume 7, Issue 1, pp 59–71 | Cite as

Molecular structure of aniline in the gaseous phase: A concerted study by electron diffraction and ab initio molecular orbital calculations

  • György Schultz
  • Gustavo Portalone
  • Fabio Ramondo
  • Aldo Domenicano
  • István Hargittai
Article

Abstract

The molecular structure of free aniline has been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF and MP2 levels of theory, using the 6-31G*(6D) basis set. Least-squares refinement of a model withC s symmetry, with constraints from MP2 calculations, has led to an accurate determination of the C-C-C angle at theipso position of the benzene ring, α=119.0±0.2‡ (where the uncertainty represents total error). This parameter provides information on the extent of the interaction between the nitrogen lone pair and the π system of the benzene ring, and could not be determined accurately by microwave spectroscopy. The angles at theortho, meta, andpara positions of the ring are 120.3±0.1‡, 120.7±0.1‡, and 119.0±0.3‡, respectively. Important bond distances are 〈rg(C-C)〉=1.398±0.003 å andrg(C-N) =1.407±0.003 å. The effective dihedral angle between the H-N-H plane and the ring plane, averaged over the large-amplitude inversion motion of the amino group, is 〈¦Τ¦〉=44±4‡. The equilibrium dihedral angle is calculated to be 41.8‡ at the HF level and 43.6‡ at the MP2 level, in agreement with far-infrared spectroscopic information. The MO calculations predict that the differencer(Cortho-Cmeta) -r(Cipso-Cortho) is 0.008–0.009 å. They also indicate that the nitrogen atom is displaced from the ring plane, on the side opposite to the amino hydrogens. The displacement is 0.049 å at the HF level and 0.072 å at the MP2 level. The two calculations, however, yield very different patterns for the minute deviations from planarity of the ring carbons.

Key words

Aniline gas-phase electron diffraction ab initio MO calculations benzene ring deformation nitrogen inversion motion 

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Copyright information

© Plenum Publishing Corporation 1996

Authors and Affiliations

  • György Schultz
    • 1
  • Gustavo Portalone
    • 2
  • Fabio Ramondo
    • 3
  • Aldo Domenicano
    • 3
  • István Hargittai
    • 1
    • 4
  1. 1.Structural Chemistry Research Group of the Hungarian Academy of SciencesEötvös UniversityBudapestHungary
  2. 2.Department of ChemistryUniversity of Rome “La Sapienza”RomeItaly
  3. 3.Department of Chemistry, Chemical Engineering and MaterialsUniversity of L'AquilaL'AquilaItaly
  4. 4.Institute of General and Analytical ChemistryBudapest Technical UniversityBudapestHungary

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