Effect of 2-Substitution on the Rearrangement of 1-Cyclopropylvinyl Cations

2-Substitution in 1-cyclopropylvinyl cations produces a steric effect on cation generation and solvent trapping, but an electronic charge-stabilizing effect on cyclopropyl-to-cyclobutyl rearrangement

A Model for Granular Texture with Steric Exclusion

We propose a new method to characterize the geometrical texture of a granular packing at the particle scale including the steric hindrance effect. This method is based on the assumption of a maximum disorder (entropy) compatible both with strain-induced anisotropy of the contact network and steric exclusions. We show that the predicted statistics for the local configurations is in a fairly agreement with our numerical data.Comment: 9 pages, 5 figure

Comparison of the atomic level structure of the plastic crystalline and the liquid phases of CBr2Cl2: neutron diffraction and Reverse Monte Carlo modeling

Neutron diffraction results obtained for plastic crystalline dichlorodibromomethane (CBr2Cl2) have been modelled by means of the Reverse Monte Carlo method. Comparison with its liquid phase is provided at several levels of the atomic structure (total scattering structure factors, partial radial distribution functions, orientational and dipole-dipole correlations). Results reveal that the relative orientation of neighbouring molecules largely depends on the steric effect. The small dipole moment has not as strong influence as the steric effect on the short range order. Our observations fit well with earlier findings presented for the series CBrnCl4-n (n=0, 1, 2, 4).Comment: 14 pages, 6 figures, accepted for publication in Journal of Physics: Condensed Matte

Computationally synthesised inorganic and organometallic complexes : a thesis presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Chemistry at Massey University, Albany, New Zealand

Catalytic aromatic ring C–H bond functionalisations by transition metal cyclometallation reactions are important for organic transformation reactions. The cyclometallated product, which contains a new metal–carbon bond is formed as a consequence of different types of carbon–hydrogen····metal (C–H····M) interactions. These C–H···M interactions have been known as anagostic, preagostic and agostic interactions. By nature, the anagostic interaction has mainly electrostatic components, the preagostic interaction has electrostatic components with some back-bonding from metal to C–H antibonding orbital involved and the agostic interaction has mainly covalent components when the C–H bond donates electron density to the partially occupied metal centre. Prior to the current thesis work, an in-depth study that addresses the influence of steric and electronic factors on the anagostic, preagostic and agostic carbon–hydrogen····metal interaction was missing. In this thesis, the influence of both the steric and electronic factors on the anagostic, preagostic and agostic C–H···M interactions has been studied. It is seen that the electronic and steric influences play differently for different ligand systems as with the flexible tetralone ligand, a maximum of steric and electronic influence results into another type of anagostic interaction named as the 'C-anagostic' interaction. It is also seen that a stronger steric and electronic effect can trigger agostic covalency at the anagostic stage of the reaction. The inflexible ligand ensures the short anagostic approach, which has some back-bonding character and the nature of the interaction lies into the preagostic category. Finally, the aromatic ring agostic interactions have more complexity as new donations named as 'syndetic' from C–C pi bond to metal antibonding orbitals were recognised which shares the same antibonding acceptor orbitals as the agostic donation does. The recognition of new bonding situations in C–H····M interactions can have significant implications for C–H bond functionalisation reactions

RNA polymerase interactions and elongation rate

We show that non-steric molecular interactions between RNA polymerase (RNAP) motors that move simultaneously on the same DNA track determine strongly the kinetics of transcription elongation. With a focus on the role of collisions and cooperation, we introduce a stochastic model that allows for the exact analytical computation of the stationary properties of transcription elongation as a function of RNAP density, their interaction strength, nucleoside triphosphate concentration, and rate of pyrophosphate release. Cooperative pushing, i.e., an enhancement of the average RNAP velocity and elongation rate, arises due to stochastic pushing. This cooperative effect cannot be explained by steric hindrance alone but requires a sufficiently strong molecular repulsion. It disappears beyond a critical RNAP density, above which jamming due to collisions takes over. For strong stochastic blocking the cooperative pushing is suppressed at low RNAP densities, but a reappears at higher densities.Comment: 26 pages, 6 figure

Steric-effect-induced enhancement of electrical-double-layer overlapping phenomena\ud

In this paper, we demonstrate that nontrivial interactions between steric effect and electrical-double-layer (EDL) overlap phenomena may augment the effective extent of EDL overlap in narrow fluidic confinements to a significant extent by virtue of rendering the channel centerline potential tending to the ζ potential in a limiting sense as the steric effect progressively intensifies. Such a behavior may result in a virtually uniform (undiminished) magnitude of the EDL potential across the entire channel height and may cause lowering of the total charge within the EDL.\ud \u

Nonproductive Events in Ring-Closing Metathesis Using Ruthenium Catalysts

The relative TONs of productive and nonproductive metathesis reactions of diethyl diallylmalonate are compared for eight different ruthenium-based catalysts. Nonproductive cross metathesis is proposed to involve a chain-carrying ruthenium methylidene. A second more-challenging substrate (dimethyl allylmethylallylmalonate) that forms a trisubstituted olefin product is used to further delineate the effect of catalyst structure on the relative efficiencies of these processes. A steric model is proposed to explain the observed trends