Structural studies of ionic liquid-modified microemulsions.

This work is focused on the influence of an ionic liquid (IL), i.e. ethyl-methylimidazolium hexylsulfate, on the spontaneous formation of microemulsions with ionic surfactants.

Influence of the core conformation on the NH-tautomerism in porphyrins: a study of meso-(1,3-dithian-2-yl)porphyrins.

In order to investigate the mechanism of the NH-tautomerism in porphyrins, three meso-dithianyl-substituted porphyrins of different substitution pattern were studied theoretically. The corresponding trans-, cis- and saddle-point geometries were optimized with DFT methods, and the macrocyclic conformations obtained were analyzed using normal-structure-decomposition (NSD) analysis. Special attention was given to the influence of the participating out-of-plane and in-plane conformations on the NH-tautomerism, and the interplay of substituents, core conformations and energies of the transition-state structures was critically evaluated.

Quantification of the (anti)aromaticity of fulvalenes subjected to pi-electron cross-delocalization.

Fulvalenes 3-12 were theoretically studied at the ab initio level of theory. For the global minima structures, the occupation of the bonding (pi)C=C orbital of the interring C=C double bond obtained by NBO analysis quantitatively proves pi-electron cross-delocalization resulting in, at least partially, 2- or 6pi-electron aromaticity and 8pi-electron antiaromaticity for appropriate moieties. The cross-conjugation was quantified by the corresponding occupation numbers and lengths of the interring C=C double bonds, while the aromaticity or antiaromaticity due to cross-delocalization of the pi-electrons was visualized and quantified by through-space NMR shielding surfaces.

Conformational landscape of meso-(1,3-dithian-2-yl)porphyrins.

An investigation of the conformational landscape of 1,3-dithian-2-yl bearing porphyrins and the rotational behavior of the dithianyl substituents in meso position was carried out by variable-temperature (VT) NMR spectroscopy. Additionally, theoretical results for alternative conformations and energy barriers were obtained by molecular modeling. The study revealed different NH trans tautomers with regard to the orientation of the dithianyl ligands for the free base porphyrins 1-3.

Synthesis of mono- and disubstituted porphyrins: A- and 5,10-A2-type systems.

General syntheses have been developed for meso-substituted porphyrins with one or two substituents in the 5,10-positions and no beta substituents. 5-Substituted porphyrins with only one meso substituent are easily prepared by an acid-catalyzed condensation of dipyrromethane, pyrrole-2-carbaldehyde, and an appropriate aldehyde using a "[2+1+1]" approach. Similarly, 5,10-disubstituted porphyrins are accessible by simple condensation of unsubstituted tripyrrane with pyrrole and various aldehydes using a "[3+1]" approach.

Electronic and steric substituent influences on the conformational equilibria of cyclohexyl esters: the anomeric effect is not anomalous!

The cyclohexyl esters of a series of carboxylic acids, RCO(2)H, spanning a range of electronegativities and quotients of steric hindrance for the R substituent (R=Me, Et, iPr, tBu, CF(3), CH(2)Cl, CHCl(2), CCl(3), CH(2)Br, CHBr(2), and CBr(3)) were prepared. Their conformational equilibria in CD(2)Cl(2) were examined by low-temperature (1)H NMR spectroscopy to study the axial or equatorial orientation of the ester functionality with respect to the adopted chair conformation of the cyclohexane ring. The ab initio and DFT geometry-optimized structures and relative free energies of the axial and equatorial conformers were also calculated at the HF/6-311G**, MP2/6-311G**, and B3LYP/6-31G** levels of theory, both in the gas phase and in solution.