Hrvoj Vančik

Mechanosynthesis of nitrosobenzenes: a proof-of-principle study in combining solvent-free synthesis with solvent-free separations

Mechanochemical Oxone oxidation of selected para-substituted anilines was used as a rapid and solvent-free route to nitrosobenzenes; besides avoiding bulk solvents and short reaction times, this method exploits high vapour pressures of nitrosobenzenes for the solvent-free separation of the product by sublimation, demonstrating an entirely solvent-free route to chemical synthesis and product isolation.

Dimethylsilylene: a trisilane and a geminal diazide as new photochemical precursors. Evidence for an absorption maximum near 450 nm

Le diazidodimethylsilane et le diphenyl-1,3 hexamethyltrisilane sont consideres comme de nouveaux precurseurs du dimethylsilylene

Crystal disordering and organic solid-state reactions

This work is the extension of our preliminary communication about the relationship between the change in the solid-state structure and the chemical reaction in a crystal. The investigation is a case study about the nature of the adiabatic organic solid-state reactions by kinetic measurements of the processes that occur during the dimerization of aromatic nitroso compounds (p-bromo- and p-iodonitrosobenzenes, respectively) in crystals. From the reaction rates at different temperatures we have calculated the activation energy. Since dimerization is induced by the appearance of crystal deformations on the surface caused by sublimation, we study here the relationship between the rate of sublimation and the rate of dimerization. There are indications that the sublimation of molecules from the surface serves only for the activation of chemical solid-state reaction. Dimerization is also studied under three different topochemical environments: strong topochemistry in the cryogenic conditions where the starting monomers were obtained by photolysis of crystals of the corresponding dimer at 14 K, looser topochemistry in the freshly sublimed crystals of monomers, and randomly distributed monomer molecules in thin layers prepared by cryogenic deposition. It is demonstrated that the change in topochemistry drastically modifies the reaction rate.

Confirmation of the H-bridged structure of the 2-butyl cation by comparison of experimental and ab initio IR frequencies

The IR spectrum of the 2-butyl cation, measured at –125 °C in an SbF5 matrix and calculated ab initio(MP2(FULL)/6-31G*), is characterized by a C(H [graphic omitted] ) C peak at 2175 cm–1 assigned to the nonclassical H-bridged (C2-symmetry) structure 1.

Opus Magnum: An Outline for the Philosophy of Chemistry

This work explores the nature of chemistry as an autonomous science and philosophical consequences of generalizations of some chemical aspects. Chemistry is regarded in its distinction from physics, going back to the alchemical aim for the ultimate experiment rather than for all explaining theory. Topology, shape, valence etc. are identified as typically chemical concepts. The contribution of chemistry to the general theory of complexity is demonstrated by approach of diminishing interactions by which smaller and smaller energy increments are needed to move from one level to another one of higher complexity.

Matrix isolation and vibrational spectroscopy of carbocations

It is reported that some unstable species, such as cyclopropylcarbinyl-, cyclooctyl-, 2-butyl- and 7-norbornyl- carbocations, can be prepared in the SbF5 matrix and investigated by IR spectroscopy combined with high level ab initio calculations. Direct measurements of the changes in bond strenghts, i.e. changes of vibrational frequencies (Av/cm-l) induced by forming the cationic species, could yield fundamental information on the neighboring group effects. Results of systematic investigations along these lines include studies of the complexes of nitriles and ketones with SbF5, ally1 and propargyl cations and chlorocarbocations.

Characteristic frequencies of hydrogen-bridged carbocations. IR spectra and ab initio calculations of the nonclassical structures of the cyclooctyl cation

The symmetrically H-bridged structure of the cyclooctyl cation is confirmed definitively by the characteristic IR vibration at 1845 cm–1 and by the agreement of the IGLO chemical shifts calculated with MP2/6-31G* geometry of the chair–boat (CS) conformation with the experimental NMR values.

Surface nucleation in solid-state dimerisation of nitrosobenzenes promoted by sublimation

The dimerisation reaction in crystals of monomeric nitrosobenzenes proceeds by the nucleation and growth mechanism with nucleation first occurring at crystals kinks followed by nucleation at edges and surfaces. Nucleation as well as the reaction rate are strongly reduced if sublimation is hindered under the corresponding experimental conditions and increased if sublimation is promoted.

Rearrangement of bicyclo[3.2.0]heptyl precursors to the 7-norbornyl cation in the cryogenic SbF5 matrix

The first direct observation by IR spectroscopy in the cryogenic SbF5 matrix was made of the rearrangement of 2- and 3-chlorobicyclo[3.2.0]heptanes (3) and (4), respectively, to the 7-norbornyl cation 1 and its subsequent transformation into the 2-norbornyl cation 5.

Reaction of Trimethylsilylacetylenes with Antimony Pentafluoride under Matrix Isolation Conditions: Experimental and Computational Study†

Reaction of trimethylsilylacetylenes Me(3)SiC≡CR with SbF(5) in the solid state was investigated using matrix isolation infrared spectroscopy and quantum-mechanical calculations. Two reaction pathways were detected. Replacement of the trimethylsilyl group with SbF(4) produces neutral antimony acetylides F(4)SbC≡CR. Acetylenic bond protonation produces silyl cation 6-R, fully bridged for R = H and SiMe(3). High total charges on the bridging SiMe(3) group and low Me(3)Si-C bond orders to acetylenic moiety, both calculated at the MP4(SDQ)/6-311G(d,p) level of theory, indicate high silyl cation character of these species.