A new way for the internal functionalization of dendrimers

The selective reaction of amines and hydrazides with only one Cl on each P(S)Cl₂ or P(O)Cl₂ end group of phosphorus dendrimers, followed by the grafting of hydroxybenzaldehyde on the remaining P-Cl functions, and the subsequent growing of the dendrimer from the aldehyde is described. Allyl and pyrene derivatives have been grafted in this way inside the dendrimers during their growing. This constitutes a new way for the internal functionalization of dendrimers.     

Gas-phase ion–molecule reactions of thioic and dithioic acid derivatives. Condensation reactions with alkenes and alkynes

A Fourier transform–ion cyclotron resonance study of thioacyl compounds as binary mixtures with unsaturated hydrocarbons has revealed that thioacetylium ions CH₃CS⁺ generated by electron fragmentation fail to thioacyl-ate even the most reactive aromatic hydrocarbons. Among the hydrocarbons studied, only 3-hexyne and 2,4-dimethyl-2,5-hexadiene were observed to react with CH₃CS⁺. Apart from proton-transfer reactions, the major ionic reaction of thioesters with arenes, alkynes and alkenes is condensation of the molecular ion of one component, usually the ester, with a neutral molecule of the other, resulting in the cleavage of the S? C_alkyl bond of the thioester. The nature of this reaction is discussed and a possible mechanism is suggested.     

The phase behavior of dodecylsulfonic acid with water: A reinterpretation

Data from visual inspection, microscopic observations through a polarizing microscope, and dilatometry on sealed samples have been used to draw a phase diagram for this two-component system that differs from the one originally published on the basis of the same data. The difference lies in the recognition of a mesophase existing in a composition region intermediate between that of the cylindrical (middle) and lamellar (neat) phases. The problems of accounting for these three types of structures include their very narrow miscibility gaps with each other, their extraordinary thermal stability, and the possible absence of any region of direct binary equilibrium between the middle and neat phases.     

Investigating bonding in small silicon-carbon clusters: exploration of the potential energy surfaces of Si3C4, Si4C3, and Si4C4 using ab initio molecular dynamics

A theoretical investigation of the properties of the Si3C4, Si4C3, and Si4C4 clusters is reported. Systematic explorations of the potential energy surfaces of the three clusters are performed using a combination of ab initio molecular dynamics and local energy minimizations using density functional theory. A large number of isomers with a large variety of geometries has been found. The geometries, energies, and vibrational frequencies yielded are discussed. Furthermore, a quantitative analysis of the interatomic distances, angles, and coordination numbers observed, as well as the conclusions on the bonding properties, are presented. The cluster properties are then compared to those of solid SiC and of the smaller Si-C clusters (with size up to 6) obtained in a previous study. Analysis of our results and comparison with bulk properties show that even clusters as small as Si3C4, Si4C3, and Si4C4 exhibit properties similar to those of the amorphous bulk, in particular as for the structures and bonds formed by C atoms.     

Coordinative Chain Transfer Polymerization of Butadiene with Functionalized Aluminum Reagents

Functionalized aluminum alkyls enable effective coordinative chain transfer polymerization with selective chain initiation by the functionalized alkyl. (ω‐Aminoalkyl)diisobutylaluminum reagents (12 examples studied) obtained by hydroalumination of α‐amino‐ω‐enes with diisobutylaluminum hydride promote the stereoselective catalytic chain growth of butadiene on aluminum in the presence of Nd(versatate)₃, Cp*₂Nd(allyl), or Cp*₂Gd(allyl) precatalysts and [PhNMe₂H⁺]/[B(C₆F₅)₄^?]. Carbazolyl‐ and indolylaluminum reagents result in efficient molecular weight control and chain initiation by the aminoalkyl rather than the isobutyl substituent bound to aluminum. As confirmed for (3‐(9H‐carbazol‐9‐yl)propyl)‐initiated polybutadiene (PBD), for example, by deuterium quenching studies, polymer chain transfer by β‐hydride transfer is negligible in comparison to back‐transfer to aluminum.     

Toward the comparison of rare earth element and actinide behavior in materials: a computational study of Ce- and U-bearing britholites

We present a computational investigation into the nature of bonds formed by f-elements in materials. The paper presents an example of the incorporation of rare earth elements (REE) and actinides in minerals derived from fluorapatite: Ca(10)(PO(4))(6)F(2). These minerals, called britholites, allow many substitutions on all three Ca, P, and F sites and are considered as potential host phases for radioactive elements separated from nuclear waste. REE and actinides have very similar physical and chemical properties, but REE are not radioactive and much more easily handled. REE are, therefore, very often used as a surrogate for actinides in experimental studies. The representative elements of rare earths and actinides chosen for this first investigation are cerium and uranium, respectively. We have studied all the various configurations of Ca(9)X(PO(4))(6)(-)(y)()(SiO(4))(y)()F(2), where X stands for Ce(3+), Ce(4+), U(3+), and U(4+), and y is equal to 1 and 2 for three-time and four-time charged cations, respectively. Calculations have been performed within the density functional theory (DFT) framework according to the computation scheme determined in a previous study. The analysis of the energies of the various configurations shows that the incorporation of all the cations considered stabilizes the apatitic structure. This stabilization, however, is greater for four-time charged cations than for three-time charged ones, which shows that Ce and U are both preferentially substituted in the +IV oxidation state. In addition, the substitution in one of the two cationic sites of the apatitic structure is always more favorable. Then, the geometry analysis shows a larger decrease in size of this cationic site for U than for Ce, as well as different volume variations for Ce and U substitutions in the two cationic sites. This cannot be explained by steric effects alone. Finally, the electronic density analysis yields three essential results: U and Ce form significantly covalent bonds, U forms bonds more covalent than Ce, and finally four-time charged cations form more covalent bonds than three-time charged ones. The comparison of these results with the formation enthalpies of the various phases shows a positive correlation between the covalence degree of the bonds formed by the f-element and the stability of the structure. In addition, our results prove that Ce- and U-bearing britholites exhibit very similar energetic, structural, and electronic properties. Ce, therefore, appears to be a good simulant for U.