Equilibrium structure of the hydrogen bonded dimer H2O ⋯ HF

The equilibrium structure of the hydrogen bonded complex H2O HF has been calculated ab initio using the CCSD(T) method with basis sets up to sextuple- quality with diffuse functions and taking into account the basis set superposition error correction. The calculations carried out confirm the importance of diffuse functions and of counterpoise correction to obtain an accurate geometry. The most important point is that the basis set convergence is extremely slow and, for this reason an accurate ab initio structure requires a very large basis set. Nevertheless, the ab initio structure is significantly different from the experimental r0 and rm structures. Analysis of the basis set convergence and of the approximations used for the determination of the experimental structures indicates that the ab initio structure is expected to be more reliable.

Absolute line intensities for formic acid and dissociation constant of the dimer

Absolute line intensities in the v6 and v8 interacting bands of trans-HCOOH, observed near 1105.4 and 1033.5 cm -1, respectively, and the dissociation constant of the formic acid dimer (HCOOH)2 have been measured using Fourier transform spectroscopy at a resolution of 0.002 cm-1. Eleven spectra of formic acid, at 296.0(5) K and pressures ranging from 14.28(25) to 314.0(24) Pa, have been recorded between 600 and 1900 cm-1 with an absorption path length of 19.7(2) cm. 437 integrated absorption coefficients have been measured for 72 lines in the v6 band. Analysis of the pressure dependence yielded the dissociation constant of the formic acid dimer, k p=361(45) Pa, and the absolute intensity of the 72 lines of HCOOH. The accuracy of these results was carefully estimated. The absolute intensities of four lines of the weak v8 band were also measured. Using an appropriate theory, the integrated intensity of the v6 and v 8 bands was determined to be 3.47 × 1017 and 4.68 × 10-19 cm-1/(molecule cm-1) respectively, at 296 K. Both the dissociation constant and integrated intensities were compared to earlier measurements. © 2007 American Institute of Physics.

Concertedness and solvent effects in multiple proton transfer reactions: The formic acid dimer in solution

The issue of multiple proton transfer (PT) reactions in solution is addressed by performing molecular dynamics simulations for a formic acid dimer embedded in a water cluster. The reactant species is treated quantum mechanically, within a density functional approach, while the solvent is represented by a classical model. By constraining different distances within the dimer we analyze the PT process in a variety of situations representative of more complex environments. Free energy profiles are presented, and analyzed in terms of typical solvated configurations extracted from the simulations. A decrease in the PT barrier height upon solvation is rationalized in terms of a transition state which is more polarized than the stable states. The dynamics of the double PT process is studied in a low-barrier case and correlated with solvent polarization fluctuations. Cooperative effects in the motion of the two protons are observed in two different situations: when the solvent polarization does not favor the transfer of one of the two protons and when the motion of the two protons is not synchronized. This body of observations is correlated with local structural and dynamical properties of the solvent in the vicinity of the reactant. (C) 2000 American Institute of Physics. [S0021-9606(00)51121-0].

The mechanism of N2O formation via the (NO)(2) dimer: A density functional theory study

Catalytic formation of N2O via a (NO)(2) intermediate was studied employing density functional theory with generalized gradient approximations. Dimer formation was not favored on Pt(111), in agreement with previous reports. On Pt(211) a variety of dimer structures were studied, including trans-(NO)(2) and cis-(NO)(2) configurations. A possible pathway involving (NO)(2) formation at the terrace near to a Pt step is identified as the possible mechanism for low-temperature N2O formation. The dimer is stabilized by bond formation between one O atom of the dimer and two Pt step atoms. The overall mechanism has a low barrier of approximately 0.32 eV. The mechanism is also put into the context of the overall NO+H-2 reaction. A consideration of the step-wise hydrogenation of O-(ads) from the step is also presented. Removal of O-(ads) from the step is significantly different from O-(ads) hydrogenation on Pt(111). The energetically favored structure at the transition state for OH(ads) formation has an activation energy of 0.63 eV. Further hydrogenation of OH(ads) has an activation energy of 0.80 eV. (C) 2004 American Institute of Physics.

Enantioselective Rhodium-Catalyzed Alkylative Desymmetrization of 3,5-Dimethylglutaric Anhydride

A rhodium-catalyzed enantioselective cross-coupling of sp³ organozinc reagents and 3,5-dimethylglutaric anhydride has been developed to afford the corresponding products, syn-deoxypolypropionates, in excellent yields and enantioselectivities. This reaction has been developed so that both commercially available and in situ prepared organozinc reagents are competent coupling partners.

New families of enantiopure cyclohexenone cis-diol, o-quinol dimer and hydrate metabolites from dioxygenase-catalysed dihydroxylation of phenols

Toluene dioxygenase-catalysed cis-dihydroxylation of phenols has led to the discovery of new enantiopure cyclohexenone cis-diol, o-quinol dimer and phenol hydrate metabolites having synthetic potential.

The structural characterization and hydroformylation activity of the tri-rhodium complex [Rh-3(mu(2)-dppm)(2)(mu(2)-CO)(3)(K-1-CO)(3)]BF4

Rh-2(cod)(2)(mu(2)-dppm)(mu(2)-Cl)]BF4 (1) rearranges under carbon monoxide to give [Rh-3(mu(2)-dppm)(2)-(mu(2)-CO)(3)(K-1-CO)(3)]BF4 (2). Complex 2 has been structurally characterized by single crystal X-ray crystallography. The hydroformylation activities of 1 and 2 were compared for substrates styrene and 1-hexene and the activity of 2 found to be unexpectedly high.