Topic
Steric effects
About: Steric effects is a research topic. Over the lifetime, 16112 publications have been published within this topic receiving 319615 citations. The topic is also known as: steric hindrance.
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122 citations
TL;DR: It is reported that single Rh atoms anchored to the edges of 2D MoS2 sheets can efficiently convert crotonalde-hyde to crotyl alcohol with 100% selectivity via a steric confinement effect of pocket-like active sites.
Abstract: Selective hydrogenation of unsaturated aldehydes to unsaturated alcohols is a valuable but challenging task for synthesizing fine chemicals. We report that single Rh atoms anchored to the edges of 2D MoS2 sheets can efficiently convert crotonaldehyde to crotyl alcohol with 100% selectivity via a steric confinement effect of pocketlike active sites. Characterization results suggest that the synthesized Rh1/MoS2 single-atom catalysts (SACs) possess a unique geometric and electronic configuration, which confines the adsorption mode of the reactant molecule by a steric effect. The DFT calculations suggest that the MoS2 sheets terminate with oxidized Mo edges and the Rh1 stably anchors at the Mo cation vacancy site, which can facilely dissociate H2 to H atoms. The dissociated H atoms spill over to react with the edge O atoms to form OH species and create an HO-Mo-Rh1-Mo-OH configuration, resembling a pocketlike active site, which confines the adsorption mode of the crotonaldehyde due to steric effects. Such specific adsorption configuration yields 100% selectivity. The strategy of constructing pocketlike active centers with single metal atoms and 2D nanosheets opens new approaches to designing highly selective SACs for specific classes of catalytic transformations.
122 citations
TL;DR: In this article, the authors compare the self-assembly of the various isomers of benzene−dicarboxylic acids at the interface between solution and graphite substrate.
Abstract: We compare the self-assembly of the various isomers of benzene−dicarboxylic acids at the interface between solution and graphite substrate. In the case of planar benzene−dicarboxylic acids it was possible to observe long-range ordered monolayers by STM. However, no ordered adsorption was observed for the nonplanar 1,2-benzene−dicarboxylic acid. By means of a control experiment with 1,2,4,5-benzene-tetracarboxylic acid, it was possible to demonstrate that the nonplanar structure is not the decisive reason for the absence of self-assembly. In fact, the direct neighborhood of the two carboxylic groups in 1,2-benzene−dicarboxylic acid does not allow for extended hydrogen-bound aggregations. Thus, the stabilization due to intermolecular hydrogen bonding is too weak for STM investigations, at least at room temperature. It has been shown that a periodic, infinitely extendable hydrogen-bonding scheme is a requirement.
121 citations
TL;DR: In this article, the authors investigated the degradation of water soluble PLA oligomers with different chain lengths and chirality at acidic pH and temperatures in the range from 40 to 120 degrees C. The time evolution of the concentrations of all oligomers was measured by HPLC and corresponding degradation rates were evaluated for each specific chain length.
121 citations
TL;DR: It is shown that the electronic and solvent effects evidenced by experimental studies can be easily counterbalanced by steric effects.
Abstract: The reaction mechanism operative in olefin metathesis has been and still is a challenging area of research. Here we contribute to the discussion showing that the actual mechanism is a balance of the title effects. In particular, we show that the electronic and solvent effects evidenced by experimental studies can be easily counterbalanced by steric effects.
121 citations