First observation of different diffusion coefficients for two conformers in a neat liquid.
Self-diffusion coefficients were studied for the highly polar liquid N-methylformamide at pressures up to 200 MPa between the melting pressure curves and 420 K by the spin-echo method. N-Methylformamide exists as a mixture of two conformers in the neat liquid. These conformers have large differences at lower temperatures in their dynamic and structural properties. The self-diffusion coefficient of the cis-conformer being 17% lower than that of the trans-conformer at the same T and p. This is the first observation of such an effect. The experimental study is supported by Monte Carlo (MC) calculations which show that the first neighbors around a cis conformer are arranged differently than in an all trans liquid. The difference leads in the simulations to a much lower dielectric constant for the trans-cis mixture and might also explain the retardation of diffusion for the cis conformer.
Chen
L
L
Institut für Biophysik und Physikalische Biochemie, Universität Regensburg, Germany.
Gross
T
T
Lüdemann
H D
HD
Krienke
H
H
Fischer
R
R
D004058:Diffusion; D005559:Formamides / Q000737:chemistry*; D007700:Kinetics; D008968:Molecular Conformation; D009010:Monte Carlo Method; D013237:Stereoisomerism
D005559:Formamides; C002950:methylformamide