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Abstract:
(2S)-3-(3',4'-Dihydroxyphenyl)alanine (L-dopa), C9H11-NO4, Mr=197.9, monoclinic, P21, a=13.619(6), b=5.232(2), c=6.062(3)Å, β=97.56(4)o, V=428.191 Å3, Z=2, Dx=1.529g cm-3, Dm=1.515g cm-1 (T=293K), λ(MoKα)=0.71069Å, μ=1.2 cm-1, F(000)=208, T=173K, R(F)=0.017 for 4208 reflections with sin θ/λ < 1.078Å-1. The electron distribution has been determined by multipole refinement with the Hansen/Coppens aspherical scattering factor expansion, including multipole terms up to octopoles for C,N and O and up to dipoles for H. The molecular dipole moment was determined as 12(2)D, within as e.s.d. of the ab initio value reported here of 11D. The bond critical-point properties of the total electron density were determined, giving negative values for V2 ρc consistent with covalent bonds, and are in fair agreement with the ab initio results. An analysis of the hydrogen-bond critical points gave small positive V2 ρ values, consistent with ionic, closed-shell interactions between the participating atoms. A set of theoretical structure factors was generated from the ab initio charge distribution and subjected to multipole refinement, to enable a more detailed comparison with experiment.
