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Fluorine atoms play an important role in all branches of chemistry and accordingly, it is very important to study their unique and varied effects systematically, in particular, the structure‐physicochemical properties relationship. The present study describes exceptional physicochemical effects resulting from a H/F exchange at the methylene bridge of gem‐difunctional compounds. The Δlog P(CF2‐CH2) values, that is, the change in lipophilicity, observed for the CH2/CF2 replacement in various α,α‐phenoxy‐ and thiophenoxy‐esters/amides, diketones, benzodioxoles and more, fall in the range of 0.6–1.4 units, which for most cases, is far above the values expected for such a replacement. Moreover, for compounds holding more than one such gem‐difunctional moiety, the effect is nearly additive, so one can switch from a hydrophilic compound to a lipophilic one in a limited number of H/F exchanges. DFT studies of some of these systems revealed that polarity, conformational preference as well as charge distributions are strongly affected by such hydrogen to fluorine atom substitution. The pronounced effects described, are a result of the interplay between changes in polarity, H‐bond basicity and molecular volume, which were obtained with a very low 'cost' in terms of molecular weight or steric effects and may have a great potential for implementation in various fields of chemical sciences. [ABSTRACT FROM AUTHOR]

A facile and efficient method is described for the cleavage of the Ar-Si bond of various aryl trimethyl silanes. These arylsilanes have readily undergone a solvent-free protodesilylation to the corresponding arenes at room temperature, when adsorbed on montmorillonite KSF (mont KSF).

The preparation of partially and completely saturated calix(4)arenes derivatives is reported and the configurational isomerism and conformation of the systems analyzed. Results show that catalytic hydrogenation of calix(4)arenes can afford saturated calixarene analogues in which one, two, or all rings have been hydrogenated. One takes on a confirmation wherein the phenol groups are oriented syn and the cyclohexanol shows an anti-down arrangement. An anti-down/gauche-down conformation was observed for the cyclohexanol rings of two distal phenols.

Reinvestigation of the molecular structure of tetracyclohexylmethane reveals that it exists in the crystal in a (g/a/-g) conformation and the rings are skewed from their perfectly staggered D2d conformation. Crystallographic conformation is the lowest energy form, as revealed by molecular mechanics calculations. Multinuclear NMR experiments reveal the occurrence of fast rotational process in these molecules, leading to topomerization. A transition state of D2d symmetry is associated with the rotational pathway involving libration of the four rings.

Tetracyclohexylethene in tongue and groove arrangement is prepared and analyzed to study the conformational phenomenon in the polycyclohexyl system. Conformations of two methylene groups at methine carbon are restricted due to the presence of a ring. Crystallographic analysis reveals the deep introduction of syn rings methine hydrogens in the grooves. Higher conformational barrier is observed due to restricted rotations of cyclohexyl rings.

Two dimensional NMR methods INADEQUATE and DQF COSY were used to assign C and H NMR of tricyclohexylmethane. Molecular mechanics computations were carried out to analyze the impact of torsional angles of the cyclohexyl rings and their patterns of attachment on the relative energy of the conformations. This was a part of the study of static and dynamic stereochemistry of tricyclohexylmethane.

The degradation of the warfare agent sulfur mustard (HD) adsorbed onto KF/[Al.sub.2][O.sub.3] sorbents is described and analyzed by MAS NMR. The detoxification of the blister agent has showed the formation of nontoxic substitution and less-toxic elimination products and the reaction rates are affected by MAS conditions.

The reaction under [S.sub.N]1 conditions of the hexabromo calixarene derivative with the appropriate nucleophile was used to prepare calix[6]arenes derivatives monosubstituted at all bridges. The reaction could use wide array of nucleophiles such as alcohols, azide ion, aniline, benzene derivatives and even with acetylacetone.

The scope of the reaction of the tetrabromocalixarene derivative with alcohols under solvolytic conditions in trifluoroethanol (TFE) or hexafluoroisopropanol (HFIP) is analyzed. The reaction of de-tert-butylated tetrabromo derivative with m-xylene in HFIP followed by methylation of the crude product has afforded the tetraxylyl derivative.

The advantages and limitations of (super 31)P diffusion NMR in corroborating the type of species that prevail in these systems are discussed. (super 31)P diffusion NMR is a useful tool for characterizing enzyme, which adduct arrays in systems where the (super 1)H NMR spectra are noninformative because of relatively short T2.

A study was conducted to analyze face selectivity during the hydrogenation of calixarene ethers. Attacks on the face of the symmetry-equivalent rings were examined using 13C nuclear magnetic resonance spectroscopy. Results indicated that the hydrogenation of atropisomers of calix(4)arene derivatives supports an exo, all-syn method. In addition, the judicious selection of the atropisomeric starting material supported control of the pattern of stereocenters in the hydrogenated product.

The stereoselective synthesis of fully hydrogenated calixarene analogues was described. Saturated (1(n))-metacyclophane derivatives incorporating in the macrocycle cyclohexanone or cyclohexanol rings have the capability to act as host molecules and as potential synthetic intermediates for the synthesis of a novel class of calixarenes and host molecules. The rotational barrier of the product RsS SsR RsS SsR was determined using the saturation transfer method.

Hydrogenation of 1,2,3,4-tetraphenylbenzene using a Pd/C catalyst results in the formation of two stereoisomeric 1,2,3,4-tetracyclohexylcyclohexane products. Fractional crystallization enables the separation of the two stereoisomers. X-ray studies of the major product reveal it to be the cis-trans-cis isomer, while the minor product has a cis-team-trans configuration. X-ray data reveal the existence of a central ring in the minor compound in a twist-boat conformation. These data indicate that four neighboring isopropyl groups are enough to make the twist-boat as the lowest energy conformation of a cyclohexyl ring.