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N. N. Ezhova G. A. Korneeva E. V. Slivinsky R. A. Aronovich 《Russian Chemical Bulletin》1995,44(1):69-73
Hydroformylation of formaldehyde to give glycolaldehyde (GA) in the presence of RhCl(PPh3)3, RhCl(CO)(PPh3)2, or the RhCl3 + PPh3 system inN,N-dimethylacetamide was studied. The hydroformylation is accompanied by the Cannizzaro-Tishchenko reaction, condensation of CH2O with GA to give C3-C16 polyoxyaldehydes (POA), and dimerization of GA. The formation of POA, which probably occurs through coordination of GA with a Rh atom, predominates among the side reactions. The optimum conditions for hydroformylation of CH2O were found to be: RhCl3 + PPh3 as the catalyst,T 383 K,
12MPa, [H2O] 1.8 mol L–1, [Rh] 2.5 · 10–3 g-at. L–1, and [CH2O] 0.03 g L–1. At a substrate conversion of 62–67 %, the selectivity of GA formation reaches 96 %, and the yield is 60–65 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 75–78, January, 1995. 相似文献
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Erdi A. Bleda Ilhan Yavuz Zikri Altun Carl Trindle 《International journal of quantum chemistry》2013,113(8):1147-1154
We use a variant of the focal point analysis to refine estimates of the relative energies of the four low‐energy torsional conformers of glycolaldehyde. The most stable form is the cis‐cis structure which enjoys a degree of H‐bonding from hydroxyl H to carbonyl O; here dihedral angles τ1 (O?C? C? O) and τ2 (C? C? O? H) both are zero. We optimized structures in both CCSD(T)/aug‐cc‐pVDZ and aug‐cc‐pVTZ; the structures agree within 0.01 Å for bond lengths and 1.0 degrees for valence angles, but the larger basis brings the rotational constants closer to experimental values. According to our extrapolation of CCSD(T) energies evaluated in basis sets ranging to aug‐cc‐pVQZ the trans‐trans form (180°, 180°) has a relative energy of 12.6 kJ/mol. The trans‐gauche conformer (160°, ±75°) is situated at 13.9 kJ/mol and the cis‐trans form (0°, 180°) at 18.9 kJ/mol. Values are corrected for zero point vibrational energy by MP2/aug‐cc‐pVTZ frequencies. Modeling the vibrational spectra is best accomplished by MP2/aug‐cc‐pVTZ with anharmonic corrections. We compute the Watsonian parameters that define the theoretical vibrational‐rotational spectra for the four stable conformers, to assist the search for these species in the interstellar medium. Six transition states are located by G4 and CBS‐QB3 methods as well as extrapolation using energies for structures optimized in CCSD(T)/aug‐cc‐pVDZ structures. We use two isodesmic reactions with two well‐established thermochemical computational schemes G4 and CBS‐QB3 to estimate energy enthalpy and Gibbs energy of formation as well as the entropy of the gas phase system. Our extrapolated electronic energies of species appearing in the isodesmic reactions produce independent values of thermodynamic quantities consistent with G4 and CBS‐QB3. © 2013 Wiley Periodicals, Inc. 相似文献
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Why it is sometimes difficult to determine the accurate position of a hydrogen atom by the semiexperimental method: Structure of molecules containing the OH or the CH3 group
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Natalja Vogt Jean Demaison Jürgen Vogt Heinz Dieter Rudolph 《Journal of computational chemistry》2014,35(32):2333-2342
The semiexperimental (SE) technique, whereby equilibrium rotational constants are derived from experimental ground‐state rotational constants and corrections based on an ab initio cubic force field, has the reputation to be one of the most accurate methods to determine an equilibrium structure ( ). However, in some cases, it cannot determine accurately the position of the hydrogen. To investigate the origins of this difficulty, the SE structures of several molecules containing either the OH or the CH3 group are determined and compared to their best ab initio counterparts. It appears that an important factor is the accuracy of the geometry used to calculate the force field, in particular when the least‐squares system is not well conditioned. In this case, the mixed regression method is often an easy way to circumvent this difficulty. © 2014 Wiley Periodicals, Inc. 相似文献
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