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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TL;DR: In this paper, product yields and selectivities, based on ultrahigh vacuum temperature-programmed desorption, are compared for 10 C2 to C8 aliphatic alcohols dosed at 100 K on highly ordered TiO2(110) with a 3.5% concentration of surface oxygen vacancies.
Abstract: Product yields and selectivities, based on ultrahigh vacuum temperature-programmed desorption, are compared for 10 C2 to C8 aliphatic alcohols dosed at 100 K on highly ordered TiO2(110) with a 3.5% concentration of surface oxygen vacancies. Dehydration to form an alkene and water typically dominates, while two other channels, dehydrogenation to form an aldehyde and re-formation of alcohol, make detectable contributions for primary alcohols. Depending on the alcohol, there are two distinct dehydration pathways: one operative at low temperature (LT, 300−425 K) and the other at high temperature (HT, 480−650 K). The HT dehydration pathway is common to all, while the LT channel is not observed for tertiary butanol and 3- and 4-octanol. The observed trends are accounted for in terms of the inductive and steric effects of the alkyl substituents.
73 citations
TL;DR: It is shown that steric and/or fit/misfit requirements of actinyl cations to the ligand cavities, among the studied complexes, are the most favorable for the bi-pyen ligand 2, because its flexibility allows for optimal metal-to-donor-atom distances.
Abstract: Formation of complexes of alaskaphyrin 1, bi-pyen 2 and bi-tpmd 3 ligands with actinyl ions AnO2(n+), An = U, Np, Pu and n = 1, 2, was studied using density functional theory (DFT) within the scalar relativistic four-component approximation. The alaskaphyrin complexes of the uranyl are predicted to have a bent conformation, in contrast to the experimentally available X-ray data. This deviation is likely due to crystal packing effects. Apart from these conformational differences, calculated geometry parameters and vibrational frequencies are in agreement with the available experimental data. The character of bonding in the complexes is investigated using bond order analysis and extended transition states (ETS) energy decomposition. Metal-to-ligand bonds can be described as primarily ionic although substantial charge transfer is observed as well. Based on ETS analysis, it is shown that steric and/or fit/misfit requirements of actinyl cations to the ligand cavities, among the studied complexes, are the most favorable for the bi-pyen ligand 2, because its flexibility allows for optimal metal-to-donor-atom distances. Planarity of the equatorial coordination sphere of the actinide atom is found to be less important than the ability of a ligand to provide optimal uranium-to-nitrogen bond lengths. Experimental differences in demetalation rates between similar alaskaphyrin, bi-pyen and bi-tpmd uranyl complexes are explained as a result of easier protonation of the Schiff-base nitrogen of the latter. Reduction potentials calculated for the uranium complexes show a good agreement with the experiment, both in relative and in absolute terms.
73 citations
TL;DR: In this paper, the pincer ligands of organotin(IV) complexes have been synthesized and characterized by 1H, 13C, and 119Sn NMR spectroscopy, MS-ESI spectrometry, and elemental analysis.
72 citations
72 citations
TL;DR: In this paper, the steric hindrance occurring between the carbonyl groups and the adjacent aromatic substituent forces the plane of the anthraquinone moiety and that of the aromatic substitusent to adopt a nearly orthogonal conformation, resulting in relatively strong carbon-π interactions that affect both the UV-Vis absorption spectrum and the reduction potential of the compound.
Abstract: In this work we present some experimental evidence of the existence of carbonyl–π electron cloud interactions. Such interactions are analogous to anion–π interactions, which have been predicted to be energetically favourable in the case of electron deficient aromatic rings. UV-Visible spectroscopy and cyclic voltammetry results obtained for 9,10-anthraquinone, 1,1′-bis-9,10-anthraquinone, poly(9,10-anthraquinone-1,4-diyl) and other 1,4-diaryl substituted anthraquinone derivatives are described. It was found that the steric hindrance occurring between the carbonyl groups and the adjacent aromatic substituent forces the plane of the anthraquinone moiety and that of the aromatic substituent to adopt a nearly orthogonal conformation, resulting in relatively strong carbonyl–π interactions that affect both the UV-Vis absorption spectrum and the reduction potential of the compound. Moreover, in the case of thiophene substituted derivatives, the torsion angle between the anthraquinone moiety and its aromatic substituent is smaller and therefore carbonyl–π interaction effects are not observed in these compounds.
72 citations