The hydroxyacetone (CH3COCH2(OH)) torsional potential and isomerization: A theoretical study

In this work we explore the torsional potentials for hydroxyacetone using second order Møller‐Plesset (MP2) and coupled‐cluster (CCSD(T)) ab initio theoretical methods. We have calculated these potential energy surfaces as a function of single OH rotation, and simultaneous OH and methyl rotation. The results indicate that the low energy isomers coupled to the reduced barrier to methyl rotation can lead to several rotamers for this species to form. The values are compared to experimental quantities and implications for astrobiological research are also addressed. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Weak and strong hydrogen bonds conducting the supramolecular framework of 1-butyl-3-(1-naphthoyl)thiourea: crystal structure,vibrational studies,DFT methods,Pixel energies and Hirshfeld surface analysis

A detailed structural and spectroscopic study of a new thiourea derivative 1-butyl-3-(1-naphthoyl)thiourea (1) is presented with the assistance of theoretical calculations. The X-ray diffraction structure analysis reveals a planar carbonylthiourea group, favoured by intra-molecular NH···O bond. The compound is arranged in the lattice as NH···O and NH···S bonded polymeric ribbons, that extend along the crystal b-axis. Molecular pairs involving N–H···S hydrogen bonds are a dominant contribution to packing stabilisation coming from coulombic component. Hirshfeld surfaces and two-dimensional-fingerprint plots show different intermolecular contacts and its relative contributions to total surface in each compound. The AIM approach shows the nature and strength of the strong and weak intramolecular interactions and the solvent effect, while NBO analysis reveals that the sulphur atom is responsible for the higher hyperconjugative stabilising energy.     

Synthesis and Characterization of Triblock Terpolymers with three Potentially Crystallisable Blocks: Polyethylene-b-poly(ethylene oxide)-b-poly(ε-caprolactone)

A first attempt was made to produce novel ABC triblock terpolymers with three potentially crystallisable blocks: polyethylene (PE), poly(ethylene oxide) (PEO), and poly(ε-caprolactone) (PCL). Polybutadiene-b-poly(ethylene oxide) diblock copolymers were synthesized by living anionic polymerization. Then, a non-catalyzed thermal polymerization of ε-caprolactone from the hydroxyl end group of the PB-b-PEO diblock precursors was performed. Finally, hydrogenation by Wilkinson catalyst produced PE-b-PEO-b-PCL triblock terpolymers. Side reactions were detected that lead to the formation of undesired PCL-b-PEO diblock copolymers, however, these impurities were successfully removed by purification. A range of triblock terpolymers with PCL and PEO minor components were prepared. Topological restrictions on the PEO middle block prevented this block from crystallizing while the complex crystallization behavior of the PE and PCL blocks was documented by DSC and WAXS measurements.     

Exploring two-state reactivity pathways in the cycloaddition reactions of triplet methylene

Spin forbidden 1,2-cycloadditions of triplet methylene to alkenes have been theoretically studied as an example of the two-state reactivity paradigm in organic chemistry. The cycloadditions of triplet methylene to ethylene and the (E)- and (Z)-2-butene isomers show spin inversion after the transition state and therefore with no effect on the reaction rate. A local analysis shows that while triplet methylene addition to alkenes leading to the formation of a biradical intermediate is driven by spin polarization, the ring closure step to yield cyclopropane is a pericyclic process. We have found that at the regions in the potential energy surface where the spin crossover is likely to occur, the spin potential in the direction of increasing spin multiplicity, mu(+)(s), tends to equalize the one in the direction of decreasing spin multiplicity, mu(-)(s). This equalization facilitates the spin transfer process driven by changes in the spin density of the system.     

Catalytic Hydrogenation of 1-Hexene with RuCI2 (TPPMS)3(DMSO) Part II: Ionic Liquid Biphasic System

RuCl2(TPPMS)3(DMSO) (complex (I)) is very soluble in the ionic liquid 1-nbutyl-3-methylimidazolium hexafluorophosphate (BMI.PF6). Complex (I) catalyzes 1-hexene hydrogenation (500 psi H2 and 100oC) in a two-phase system, with 80% conversion in 24 h, with little substrate isomerization. Changes in catalytic behavior with temperature, pressure, time and substrate/catalyst relation are presented. Complex (I) shows good stability and can be reused several times with little activity loss. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electronic contributions to the sigma(p) parameter of the Hammett equation

A statistical procedure to obtain the intrinsic electronic contributions to the Hammett substituent constant sigma(p) is reported. The method is based on the comparison between the experimental sigma(p) values and the electronic electrophilicity index omega evaluated for a series of 42 functional groups commonly present in organic compounds.     

The maximum hardness and minimum polarizability principles as the basis for the study of reaction profiles

New and useful aspects of chemical reactivity as described by reactivity indexes and used in connection with the maximum hardness and minimum polarizability principles (MHP and MPP, respectively) are discussed and illustrated for two classical reactions in organic chemistry. They include the Beckmann rearrangement and the condensation reactions of -amino acids. The MPP appears as a more general rule than the MHP. Another relevant result is related to the usefulness of both empirical reactivity rules to predict the most probable reaction mechanism among two different pathways displaying very close values in activation energy (competitive pathways). This is illustrated for the condensation reaction of a series of -amino acids: while the accepted stepwise route follows both the MHP and MPP rules, the alternative concerted channel does not, yet its associated activation energy is slightly lower than that corresponding to the nonconcerted reaction mechanism.From the Proceedings of the 28th Congresco de Quimicos Teóricos de Expresión Latina (QUITEL 2002)