Get access

Fluorine Substitution Effects on Flexibility and Tunneling Pathways: The Rotational Spectrum of 2-Fluorobenzylamine

Authors

  • Dr. Camilla Calabrese,

    1. Dipartimento di Chimica “Giacomo Ciamician”, Università degli Studi di Bologna via Selmi 2, 40126 Bologna (Italy)
    Search for more papers by this author
  • Dr. Assimo Maris,

    1. Dipartimento di Chimica “Giacomo Ciamician”, Università degli Studi di Bologna via Selmi 2, 40126 Bologna (Italy)
    Search for more papers by this author
  • Dr. Luca Evangelisti,

    1. Dipartimento di Chimica “Giacomo Ciamician”, Università degli Studi di Bologna via Selmi 2, 40126 Bologna (Italy)
    Search for more papers by this author
  • Prof. Walther Caminati,

    1. Dipartimento di Chimica “Giacomo Ciamician”, Università degli Studi di Bologna via Selmi 2, 40126 Bologna (Italy)
    Search for more papers by this author
  • Prof. Sonia Melandri

    Corresponding author
    1. Dipartimento di Chimica “Giacomo Ciamician”, Università degli Studi di Bologna via Selmi 2, 40126 Bologna (Italy)
    • Dipartimento di Chimica “Giacomo Ciamician”, Università degli Studi di Bologna via Selmi 2, 40126 Bologna (Italy)

    Search for more papers by this author

Abstract

The effect of ring fluorination on the structural and dynamical properties of the flexible model molecule 2-fluorobenzylamine has been studied by rotational spectroscopy in free-jet expansion and quantum chemical methods. The complete potential energy surface originating from the flexibility of the aminic side chain has been calculated at the B3LYP/6-311++G** level of theory and the stable geometries were also characterized with MP2/6-311++G**. The rotational spectra show the presence of two of the predicted four stable conformers: the global minimum (I), in which the side chain’s dihedral angle with the phenyl plane is almost perpendicular, is stabilized by an intramolecular hydrogen bond between the fluorine atom and one hydrogen of the aminic group; and a second conformer II (EIIEI≈5 kJ mol−1) in which the dihedral angle is smaller and the amino group points towards the aromatic ortho hydrogen atom. This conformation is characterized by a tunneling motion between two equivalent positions of the amino group with respect to the phenyl plane, which splits the rotational transition. The ortho fluorination increases, with respect to benzylamine, the tunneling splitting of this motion by four orders of magnitude. The motion is analyzed with a one-dimensional flexible model, which allows estimation of the energy barrier for the transition state as approximately 8.0 kJ mol−1.

Get access to the full text of this article

Ancillary