Božo Plesničar

Dihydrogen trioxide clusters, (HOOOH)n (n = 2−4) and the hydrogen-bonded complexes of HOOOH with acetone and dimethyl ether: implications for the decomposition of HOOOH

Hydrogen-bonded gas-phase molecular clusters of dihydrogen trioxide (HOOOH) have been investigated using DFT (B3LYP/6-311++G(3df,3pd)) and MP2/6-311++G(3df,3pd) methods. The binding energies, vibrational frequencies, and dipole moments for the various dimer, trimer, and tetramer structures, in which HOOOH acts as a proton donor as well as an acceptor, are reported. The stronger binding interaction in the HOOOH dimer, as compared to that in the analogous cyclic structure of the HOOH dimer, indicates that dihydrogen trioxide is a stronger acid than hydrogen peroxide. A new decomposition pathway for HOOOH was explored. Decomposition occurs via an eight-membered ring transition state for the intermolecular (slightly asynchronous) transfer of two protons between the HOOOH molecules, which form a cyclic dimer, to produce water and singlet oxygen (Delta (1)O 2). This autocatalytic decomposition appears to explain a relatively fast decomposition (Delta H a(298K) = 19.9 kcal/mol, B3LYP/6-311+G(d,p)) of HOOOH in nonpolar (inert) solvents, which might even compete with the water-assisted decomposition of this simplest of polyoxides (Delta H a(298K) = 18.8 kcal/mol for (H 2O) 2-assisted decomposition) in more polar solvents. The formation of relatively strongly hydrogen-bonded complexes between HOOOH and organic oxygen bases, HOOOH-B (B = acetone and dimethyl ether), strongly retards the decomposition in these bases as solvents, most likely by preventing such a proton transfer.

Crystalline hydrogen bonded adducts of oxygen bases with peroxybenzoic acids

Abstract The preparation and isolation of several crystalline 1 : 1 adducts of substituted peroxybenzoic acids with triphenylphosphine oxide, triphenylarsine oxide, and pyridine oxides, is reported. Infrared spectra indicate the presence of strong intermolecular hydrogen bonds in these adducts.

Paper chromatography of some isomeric monosubstituted peroxybenzoic acids

The Rb values of a number of isometric monosubstituted peroxybenzoic acids have been determined for two different solvent systems. The solvent systems are hexane saturated with dioxane and dimethyl formamide for use on acetylated paper and benzene for use on paper impregnated with N-methylformamide. The Rb values of isomeric peracids vary considerably, depending on the substituent group and its orientation. An attempt is made to correlate the chromatographic data with the structure of the compounds. The influence of the strong inductive and steric effects of the substituents is cleary seen.

Calorimetric, 1H nuclear magnetic resonance, and molecular orbital studies of hydrogen bonding between peroxy acids and oxygen bases. Implications for mono-oxygen donation potential of peroxy acids

The enthalpies of formation of hydrogen-bonded complexes between peroxybenzoic acids and various oxygen bases, ΔH°, were obtained by calorimetry. The 1H n.m.r. shifts of the OOH absorptions, under conditions of complete peroxy acid complexation, were measured. ΔH° and ‘hydrogen-bond shifts’, ΔδOOH =δOOH(base)–δOOH(CCl4), were found to be sensitive to the acidity of the peroxy acid as well as the basicity of the oxygen base. A satisfactory linear correlation between ΔH° and ΔδOOH, expressed by the equation –ΔH°(kJ mol–1)=(7.59 ± 0.92)ΔδOOH +(7.35 ± 1.61), was found. Ab initio MO SCF calculations (STO-4G, 4–31 G*) were carried out for the peroxyformic acid–dimethyl ether complex and peroxyformate ion. The peroxy acid isotope effect for epoxidation of cyclohexene with 4-t-butylperoxybenzoic acid (OH/OD) in NN-dimethylacetamide (kH/kD1.09), together with the results of kinetic studies in other oxygen bases as solvents, suggest that oxygen base is most probably a part of an ‘early’, loose charge-transfer-type transition state for these reactions (‘direct attack mechanism’), and that reduced reactivity of peroxy acids in basic solvents most probably reflects lowered electrophilicity of the peroxy acid due to the forcing of the enlarged negative charge on the terminal oxygen atom after complexation.

The infrared spectra of peroxybenzoic acids—II: Disubstituted peroxybenzoic acids

Abstract Bands characteristic of the peroxycarboxyl group are described for a number of disubstituted peroxybenzoic acids. The evidence suggests probable non-equivalency of intermolecular hydrogen bonds in the investigated 2,5-disubstituted peroxybenzoic acids in the solid state.

The nature of hydrogen bonding in hydrotrioxides of methyl α-methylbenzyl ether and α-methylbenzyl alcohol. Are hydrotrioxides self-associated in solutions?

1 H and 13C N.m.r. spectroscopic evidence supports the hypothesis of the self-association of hydrotrioxides (2a) and (2b); inspection of molecular models of dimeric forms of these hydrotrioxides by taking into account the equilibrium geometry of methyl hydrotrioxide, calculated by the ab initio method at the STO 4-31G level, reveals two nearly optimal hydrogen bonding geometries in the associated hydrotrioxide species.

A molecular orbital study of the mechanism of the oxidation of acetylene by peroxyformic acid

The restricted Hartree–Fock level of ab initio theory has been used to study the reaction of peroxyformic acid with acetylene. Various plausible directions of the peroxy-acid approach to acetylene, believed to lead to molecular arrangements of both components which are near the transition state for the formation of oxiren, were investigated. The unsymmetrical attack of the peroxy-acid on acetylene is energetically more favourable than the symmetrical one. The peroxy-acid approach appears to be dominated by charge-transfer interactions. Theoretical investigation of the second-step of reaction, i.e. the oxidation of oxiren to 2,4-dioxabicyclo[1.1.0]butane, shows that such a molecule cannot exist. Nevertheless, the possibility of a diradical state for this species cannot be ruled out.

The determination of organic peroxy compounds : V. The mechanism of the chromatographic separation of symmetrically substituted dibenzoyl peroxides on various sorbents

Abstract The RF values of seventeen isomeric substituted dibenzoyl peroxides on aluminium oxide, treated and untreated cellulose and silica gel are given. The best separations were obtained on silica gel and dimethylformamide impregnated paper. The so-called “ortho effect” and the effect of substituents on the migration behaviour of compounds under investigation are discussed.

Research notesThe infrared spectra of peroxybenzoic acids—II: Disubstituted peroxybenzoic acids

Abstract Bands characteristic of the peroxycarboxyl group are described for a number of disubstituted peroxybenzoic acids. The evidence suggests probable non-equivalency of intermolecular hydrogen bonds in the investigated 2,5-disubstituted peroxybenzoic acids in the solid state.

Chromatography of isomeric peroxybenzoic acids II. The thin-layer chromatographic separation mechanism of isomeric mono- and disubstituted peroxybenzoic acids on various polyamide and cellulose adsorbents

Abstract The migration behaviour of several mono- and disubstituted peroxybenzoic acids has been studied on seven thin-layer chromatographic adsorbents. Some effects of the molecular structure of the peroxy acids on their chromatographic behaviour and the interactions between the stationary or the mobile phase and peroxy acids are discussed