Jump to main content
Jump to site search
PLANNED MAINTENANCE Close the message box

Scheduled maintenance work on Wednesday 27th March 2019 from 11:00 AM to 1:00 PM (GMT).

During this time our website performance may be temporarily affected. We apologise for any inconvenience this might cause and thank you for your patience.

Issue 29, 2010
Previous Article Next Article

Large-amplitude vibrations of an N–H⋯π hydrogen bonded cis-amide–benzene complex

Author affiliations


The ground-state N–H⋯π interaction of 2-pyridone·benzene (2PY·Bz) has been studied by infrared-UV depletion spectroscopy of the supersonic-jet cooled complex [P. Ottiger et al., J. Phys. Chem. B (2009) 113, 2937]. Here, we investigate the large-amplitude vibrations of 2PY·Bz and its d1-2PY and benzene-d6 isotopologues in the S1 state, using two-color resonant two-photon ionization and UV-holeburning spectroscopies, complemented by RI-CC2 and SCS-RI-CC2 calculations of the S1 state. The latter predict a tilted T-shaped structure with an N–H⋯π hydrogen bond to the benzene ring, similar to the S0 state. The binding energy is predicted to increase by 1.5 kJ mol−1 upon S1S0 excitation, in close agreement with the experimental value of 1.2 kJ mol−1. The vibronic band structure up to 60 cm−1 above the 000 band is dominated by large-amplitude δ tilting excitations, reflecting a change in the tilt angle of the T-shaped complex. The S0 and S1 state δ potentials were fitted to experiment, yielding a single minimum in the S0 state and a double-minimum S1 potential with δmin = ±13 degrees. The second large-amplitude vibration is the θ twisting or benzene internal-rotation mode. Due to the C6 symmetry of the benzene moiety the S0 and S1 state θ potentials are sixfold symmetric. Analysis of the θ band structure reveals that the S0 and S1θ potentials are mutually aligned and that the internal rotation barriers are V6(S0) < 0.2 kJ mol−1 and V6(S1) = 0.10(1) kJ mol−1, in close agreement with the calculations. Weaker excitations of the totally symmetric intermolecular vibrations χ (shear), ω (bend) and σ (stretch) vibrations are also observed. The 2PY intramolecular ν1 overtone, corresponding to an 2PY amide out-of-plane twist distortion, lies ∼30% higher than in bare 2PY, reflecting the hindrance of this motion by the strong N–H⋯π interaction.

Graphical abstract: Large-amplitude vibrations of an N–H⋯π hydrogen bonded cis-amide–benzene complex

Back to tab navigation

Supplementary files

Publication details

The article was received on 29 Jan 2010, accepted on 16 Mar 2010 and first published on 18 May 2010

Article type: Paper
DOI: 10.1039/C002056G
Citation: Phys. Chem. Chem. Phys., 2010,12, 8208-8218

  •   Request permissions

    Large-amplitude vibrations of an N–H⋯π hydrogen bonded cis-amide–benzene complex

    C. Pfaffen, H. Frey, P. Ottiger, S. Leutwyler, R. A. Bachorz and W. Klopper, Phys. Chem. Chem. Phys., 2010, 12, 8208
    DOI: 10.1039/C002056G

Search articles by author