I recognize that steric strain is about interactions between substituents on the front and back atoms (in terms of Newman projections), and that torsional strain is about dihedral angles in terms of eclipsed vs staggered though both concepts are just a matter of electron repulsion it seems. For example, if I have drawn 1,2 dibromoethane in the staggered position with the bromines 60 degrees apart there is presumably steric strain. If I draw then 0 degrees apart, there is also steric strain. If I draw them 180 apart, there is still steric strain. The anti conformation is lower in energy than the eclipsed, but is this lowering being attributed to a reduction in torsional strain from increasing the dihedral angle, or is it from the smaller degree of steric strain? I.e. steric interaction obviously changes when two atoms are brought closer to one and other, but by definition, bringing them closer is a matter of dihedral angle and torsional strain. How are these two concepts distinguished conceptually?
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c05172
You-Quan Zou, Dawei Zhang, Tanya K. Ronson, Andrew Tarzia, Zifei Lu, Kim E. Jelfs, and Jonathan R. Nitschke
https://ift.tt/3wqMZn1
Cobalt porphyrin atropisomers with similar electronic structures but dissimilar steric effects were synthesized. One isomer is selective for the 2 e− ORR, one is selective for the 4 e− ORR, while the other two show poor selectivity for either 2 e− or 4 e− ORR.
Abstract
Achieving a selective 2 e− or 4 e− oxygen reduction reaction (ORR) is critical but challenging. Herein, we report controlling ORR selectivity of Co porphyrins by tuning only steric effects. We designed Co porphyrin 1 with meso‐phenyls each bearing a bulky ortho‐amido group. Due to the resulted steric hinderance, 1 has four atropisomers with similar electronic structures but dissimilar steric effects. Isomers αβαβ and αααα catalyze ORR with n=2.10 and 3.75 (n is the electron number transferred per O2), respectively, but ααββ and αααβ show poor selectivity with n=2.89–3.10. Isomer αβαβ catalyzes 2 e− ORR by preventing a bimolecular O2 activation path, while αααα improves 4 e− ORR selectivity by improving O2 binding at its pocket, a feature confirmed by spectroscopy methods, including O K‐edge near‐edge X‐ray absorption fine structure. This work represents an unparalleled example to improve 2 e− and 4 e− ORR by tuning only steric effects without changing molecular and electronic structures.
https://ift.tt/3c8OTBn
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c03042
Yang Xie, Jian Li, Cong Lin, Bo Gui, Chunqing Ji, Daqiang Yuan, Junliang Sun, and Cheng Wang
https://ift.tt/3eUZWxY
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c01931
Jacopo Tessarolo, Haeri Lee, Eri Sakuda, Keisuke Umakoshi, and Guido H. Clever
https://ift.tt/32Nrobd
Can someone explain why A is wrong? I thought reducing steric hinderance would make it a stronger base. So if the chlorine atom decreases the steric hindrance, it would then make it a stronger base (NH2CL) then fluoroamine (NH2F). I don't understand the explanation in red.
Which one of the following best explains why fluoroamine (NH2F) is a weaker Lewis base than chloroamine (NH2Cl) and ammonia (NH3)?
A. The chlorine atom decreases the steric hindrance at the basic site.
B. The fluorine atom removes more electron density from the nitrogen. Correct Answer
C. Chlorine is a stronger base than fluorine. Your Answer
D. Chlorine changes the geometry of the molecule, thereby increasing the acidity.
Explanation: Choices A is incorrect. If the chlorine atom decreases the steric hindrance at the basic site, chloroamine should then be a weaker Lewis base (ligand) than fluoramine—but this contradicts what the question tells us, thus it is incorrect.
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c00779
Peng-Fei Cui, Xin-Ran Liu, Shu-Ting Guo, Yue-Jian Lin, and Guo-Xin Jin
https://ift.tt/3fe6OrW
London dispersion (LD) interactions facilitate the enantioselectivity in the Corey–Bakshi–Shibata (CBS) reduction. Employing a combination of computational and experimental studies, we provide a modern view on the origin of enantioselectivity in this powerful organocatalyzed reaction. The results demonstrate that attractive LD interactions between the catalyst and the substrate rather than steric repulsion determine the selectivity.
Abstract
The well‐known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
https://ift.tt/3kG41Hd
Mixed up five parts butter to one part steric acid and as the mixture cooled the stetic acid dropped to the bottom. I have also mixed cocoa butter and steric acid which didn't separate. Anyone else see this with butter mixtures?
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c05605
Zhigang Lyu, Yue Zhao, Zakey Yusuf Buuh, Nicole Gorman, Aaron R. Goldman, Md Shafiqul Islam, Hsin-Yao Tang, and Rongsheng E. Wang
https://ift.tt/35zdZ8C
https://preview.redd.it/dc1rmzrroyq51.png?width=948&format=png&auto=webp&s=eb9896640f1afd49aac8c0b6402a38f4db65d940
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c09802
Justin R. Houser, Carl C. Hayden, D. Thirumalai, and Jeanne C. Stachowiak
https://ift.tt/3fxO2Kv
Which C−H bond? The iridium‐catalysed C−H borylation reaction is a powerful method for the preparation of aromatic organoboronate esters. Sterically regulated regioselectivity dominates carbocyclic aromatic C−H borylation. In contrast, heterocyclic aromatics display a much greater influence from electronic effects. In this review, examples of heterocyclic C−H borylation are surveyed, and the origins of heterocyclic C−H borylation regioselectivities discussed.
Abstract
The iridium‐catalysed borylation of aromatic C−H bonds has become the preferred method for the synthesis of aromatic organoboron compounds. The reaction is highly efficient, tolerant of a broad range of substituents and can be applied to both carbocyclic and heterocyclic substrates. The regioselectivity of C−H activation is dominated by steric considerations and there have been considerable efforts to develop more selective processes for less constrained substrates. However, most of these have focused on benzenoid‐type substrates and in contrast, heteroarenes remain much desired but more challenging substrates, with the position and/or nature of the heteroatom(s) significantly affecting reactivity and regioselectivity. This Review will survey the borylation of heteroarenes, focusing on the influence of steric and electronic effects on regiochemical outcome and, by linking to current mechanistic understandings, will provide insights to what is currently possible and where further developments are required.
https://ift.tt/33GtKs0
The role of spatial arrangement : Owing to ligand rigidity and spatial demand, the stabilization of a rare S = spin ground state for tetracoordinate CoIV becomes possible, yielding a complex with high thermal stability and potential for applications relying on atomic layer deposition.
Abstract
Attempted preparation of a chelated CoII β‐silylamide resulted in the unprecedented disproportionation to Co0 and a spirocyclic cobalt(IV) bis(β‐silyldiamide): [Co[(NtBu)2SiMe2]2] (1 ). Compound 1 exhibited a room‐temperature magnetic moment of 1.8 B.M. and a solid‐state axial EPR spectrum diagnostic of a rare S= configuration for tetrahedral CoIV. Ab initio semicanonical coupled‐cluster calculations (DLPNO‐CCSD(T)) revealed the doublet state was clearly preferred (−27 kcal mol−1) over higher spin configurations only for the bulky tert‐butyl‐substituted analogue. Unlike other CoIV complexes, 1 had remarkable thermal stability, and was demonstrated to form a stable self‐limiting monolayer in preliminary atomic layer deposition (ALD) surface saturation experiments. The ease of synthesis and high stability make 1 an attractive starting point to investigate otherwise inaccessible CoIV intermediates and for synthesizing new materials.
https://ift.tt/2SBJKHu
I learnt a long while ago about the Lennard-Jones potential which has an attractive part due to van der Waals interactions and a repulsive part due to the Pauli exclusion principle when the charge distributions of atoms start to overlap. Now I’m taking a chemistry course and learning about nanoparticle interactions and there’s pretty much the same behavior as the atoms I’ve learnt about before, except for some details concerning the size of nanoparticles and ligands etc. And then this thing that’s supposedly the reason nanoparticles can’t “touch”, called the steric repulsion. According to the lecturer this is impossible to do quantum mechanical calculations on, but I’m still wondering; is steric repulsion due to the Pauli exclusion principle in some way?
Several H−H bond forming pathways have been proposed for the hydrogen evolution reaction (HER). Revealing these HER mechanisms is of fundamental importance for the rational design of catalysts and is also extremely challenging. Herein we report an unparalleled example of switching between homolytic and heterolytic HER mechanisms. We designed and synthesized three nickel(II) porphyrins with distinct steric effects by introducing bulky amido moieties to ortho‐ or para‐positions of the meso‐phenyl groups. We furthermore showed their different catalytic HER behaviors. For these Ni porphyrins, although their 1e‐reduced forms are active to reduce trifluoroacetic acid, the resulted Ni hydrides − depending on the steric effects of porphyrin rings − have different pathways to make H2. Understanding HER processes, especially controllable switching between homolytic and heterolytic H−H bond formation pathways through molecular engineering, is unprecedented in fundamentals of electrocatalysis.
https://ift.tt/2Vu27Au
Control of the selectivity of the oxygen reduction reaction through tuning of molecular steric effects is demonstrated by Ran Long, Rui Cao et al. in their Communication (DOI: 10.1002/anie.202102523). Selective two‐ or four‐electron oxygen reductions can be achieved by using Co porphyrin atropisomers with similar electronic structures but dissimilar steric effects. This work represents an unparalleled example to improve oxygen reduction selectivity by tuning only steric effects of catalysts without changing molecular and electronic structures.
https://ift.tt/3vk7scf
Achieving a s elective 2e − or 4e − oxygen reduction reaction (ORR) is critical but challenging. Herein, we report controlling ORR selectivity of Co porphyrins by tuning only steric effects. We designed Co porphyrin 1 with meso ‐phenyls each bearing a bulky ortho ‐amido group. Due to the resulted steric hinderance, 1 has four atropisomers with similar electronic structures but dissimilar steric effects. Isomers αβαβ and αααα catalyze ORR with n = 2.10 and 3.75 ( n is the electron number transferred per O 2 ), respectively, but ααββ and αααβ show poor selectivity with n = 2.89‐3.10. Isomer αβαβ catalyzes 2e − ORR by preventing a bimolecular O 2 activation path, while αααα improves 4e − ORR selectivity by improving O 2 binding at its pocket, a feature confirmed by spectroscopy methods, including O K‐edge near‐edge X‐ray absorption fine structure . This work represents an unparalleled example to improve 2e − and 4e − ORR by tuning only steric effects without changing molecular and electronic structures.
https://ift.tt/3c8OTBn
Can somebody please help me understand how the steric effect decreases acidity of a molecule?
The well‐known Corey‐Bakshi‐Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, here we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate rather than steric repulsion determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
https://ift.tt/3kG41Hd
