Hydrogen atom mediated Stone-Wales rearrangement of pyracyclene: a model for annealing in fullerene formation.

We have investigated the Stone-Wales (SW) rearrangement of pyracyclene (C(14)H(12)) using quantum mechanical molecular modeling. Of particular interest in this study is the effect of an added hydrogen atom on the barriers to SW rearrangement. Hydrogen atoms are found in high abundance during combustion, and their effect upon isomerization of aromatic compounds to more stable species may play an important role in the combustion synthesis of fullerenes. We have calculated the barriers for the SW rearrangement in pyracyclene using density functional theory B3LYP/6-31G(d) and B3LYP/6-311G(d,p). Two mechanisms have been investigated: (i) a mechanism with two identical transition states of C(1) symmetry and a cyclobutyl intermediate and (ii) a mechanism with one transition state containing an sp(3) carbon (J. Am. Chem. Soc. 2003, 125, 5572-5580; Nature 1993, 366, 665-667). We find that the barriers for these mechanisms are 120.0 kcal mol(-1) for the cyclobutyl mechanism and 130.1 kcal mol(-1) for the sp(3) mechanism. Adding a hydrogen atom to the internal bridge carbon atoms of pyracyclene reduces the barrier of the cyclobutyl mechanisms to 67.0 kcal mol(-1) and the sp(3) mechanism to 73.1 kcal mol(-1). The bonding of carbon atoms in pyracyclene is similar to those found in isomers of C(60), and the barriers are low enough so that these reactions can become significant during fullerene synthesis in flames. Adding hydrogen atoms to the external bridge atoms on pyracyclene produces a smaller reduction in the SW barrier and adding hydrogen atoms to nonbridge external carbon atoms results in no reduction of the barrier.

New lubricants from vegetable oil: cyclic acetals of methyl 9,10-dihydroxystearate.

Potential new lubricants and fuel lubricity enhancers have been prepared from methyl 9,10-dihydroxystearate and long chain aldehydes to form the corresponding cyclic acetals. These materials are oils down to low temperatures, as compared to symmetric ketals derived from the same diol, which are waxes at room temperature. The acetals form in an equilibrium reaction (Keq approximately 60) which suggests they will be stable as fuel additives. The viscosities of the new oils are close to those predicted for normal paraffins with the same number of non-hydrogen atoms, but the acetal structure has subtle effects on viscosity as compared to branched alkanes. Acetals with long alkyl branches maintain higher viscosity on a molecular weight basis compared to branched alkanes. The qualitative relationship between branch length and viscosity is discussed. These acetals are potential candidates for novel biobased lubricants.

Stable water-oil emulsions from the new insoluble surfactant sodium 5-(1-dodecylaminocarbonyl) picolinate.

The new compound sodium 5-(1-dodecylaminocarbonyl) picolinate (NaDPA) has been prepared and found to have the unusual surfactant property of forming stable water-oil (w/o) emulsions in the presence of water and a variety of organic liquids. A study of droplet size (diameters=0.1-1.0 mm) as a function of the amount of surfactant used shows that a near constant coverage of surfactant molecules exists at the water-oil interface and that the interface is made up of multiple layers. The structure of NaDPA, with its multiple hydrogen-bonding possibilities, probably contributes to the observed stability of the emulsions. The emulsions are made up of droplets that are stable for months and can be filled with dyes, buffers, and solutions of high ionic strength.

A novel method for the templated synthesis of homogeneous samples of hollow carbon nanospheres from cellulose chars.

A novel method for the production of homogeneous samples of hollow carbon nanospheres is reported from cellulose, an inexpensive and renewable precursor. The nanospheres are of diameter 50 nm, graphitic wall thickness 5-10 nm, and can easily be produced in several hundred milligram batches. The nanospheres are derived from the laser pyrolysis of a nickel chloride templated cellulose char via open Ni-core shells.