Benchmark study of molecules with large-amplitude ring-twisting motion: accurate equilibrium structure of succinic anhydride from gas electron diffraction data and coupled-cluster computations

• Published in: Structural chemistry 2015-12, Vol.26 (5-6), p.1481-1488
• Main Authors: Vogt, Natalja, Altova, Ekaterina P., Ksenafontov, Denis N., Rykov, Anatolii N.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Computer Applications in Chemistry; Original Research; Physical Chemistry; Theoretical and Computational Chemistry
• ISSN: 1040-0400; 1572-9001
• DOI: 10.1007/s11224-015-0654-0

The gas electron diffraction (GED) study of succinic anhydride (dihydro-2,5-furandione) is used as a benchmark example for the reliable determination of the structure of floppy molecules with saturated non-rigid ring. According to results of B3LYP calculations, the molecule has a planar skeleton (C 2v total symmetry), whereas the MP2 optimized structure has a non-planar ring with the torsional angle φ (C–C–C–C) of up to 11° (C 2 symmetry). It has been revealed that the increase in the quality of ab initio calculations up to CCSD(T) level and the enlargement of basis set up to quadruple- ζ size decrease the non-planarity of the molecular skeleton, which is approximated to be planar in the best-estimated ab initio structure. The semiexperimental equilibrium structure ( r e se ) has been determined from the GED data with the application of the so-called dynamic (pseudo-conformer) model describing the large-amplitude ring-twisting motion. Vibrational corrections Δ( r a  −  r e ) to the experimental internuclear distances have been calculated from the B3LYP/cc-pVTZ quadratic and cubic force constants. The best-estimated ab initio structure agrees well with the r e se structure. This fact points to the reliability and a high accuracy of both experimental data and applied theory.