Enantioselective [2,3]-Sigmatropic Rearrangements: Metal-Bound or Free Ylides as Reaction Intermediates?

Density functional theory calculations were applied to study four previously published metal-catalyzed [2,3]-rearrangements from onium ylide intermediates, in pursuit of generalizations about when, during these types of reactions, catalysts dissociate. Our results corroborate past studies where free ylide mechanisms were proposed to be operative. Calculations on case studies predict that the origin of metal-catalyst ‘falling off’ (dissociation) can be attributed primarily to the steric bulkiness of functional groups adjacent to the carbene carbon.

Download Full-text

Metal-Bound or Free Ylides as Reaction Intermediates in Metal-Catalyzed [2,3]-Sigmatropic Rearrangements? It Depends.

10.26434/chemrxiv.13175327.v1 ◽

2020 ◽

Author(s):

Croix Laconsay ◽

Dean Tantillo

Keyword(s):

Density Functional Theory ◽

Case Studies ◽

Functional Groups ◽

Density Functional ◽

Density Functional Theory Calculations ◽

Metal Catalyst ◽

Reaction Intermediates ◽

Functional Theory ◽

Sigmatropic Rearrangements ◽

Metal Catalyzed

Density functional theory calculations were applied to study four previously published metal-catalyzed [2,3]-rearrangements from onium ylide intermediates, in pursuit of generalizations about when, during these types of reactions, catalysts dissociate. Our results corroborate past studies where free ylide mechanisms were proposed to be operative. Calculations on case studies predict that the origin of metal-catalyst ‘falling off’ (dissociation) can be attributed primarily to the steric bulkiness of functional groups adjacent to the carbene carbon.

Download Full-text

Analyzing reactions of single mechanoenzyme molecules by light microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122538 ◽

1992 ◽

Vol 50 (1) ◽

pp. 426-427

Author(s):

Jeff Gelles

Keyword(s):

Image Processing ◽

Reaction Mechanisms ◽

Transient State ◽

Nanometer Scale ◽

Reaction Intermediates ◽

Enzyme Molecule ◽

Directed Movement ◽

Enzyme Molecules ◽

Individual Enzyme ◽

Single Reaction

Mechanoenzymes are enzymes which use a chemical reaction to power directed movement along biological polymer. Such enzymes include the cytoskeletal motors (e.g., myosins, dyneins, and kinesins) as well as nucleic acid polymerases and helicases. A single catalytic turnover of a mechanoenzyme moves the enzyme molecule along the polymer a distance on the order of 10−9 m We have developed light microscope and digital image processing methods to detect and measure nanometer-scale motions driven by single mechanoenzyme molecules. These techniques enable one to monitor the occurrence of single reaction steps and to measure the lifetimes of reaction intermediates in individual enzyme molecules. This information can be used to elucidate reaction mechanisms and determine microscopic rate constants. Such an approach circumvents difficulties encountered in the use of traditional transient-state kinetics techniques to examine mechanoenzyme reaction mechanisms.

Download Full-text

ANION PHOTOELECTRON IMAGING SPECTROSCOPY OF REACTION INTERMEDIATES IN THE OZONOLYSIS OF ISOPRENE

Proceedings of the 74th International Symposium on Molecular Spectroscopy ◽

10.15278/isms.2019.fd08 ◽

2019 ◽

Author(s):

Michael Thompson ◽

Caroline Chick Jarrold ◽

Marissa Dobulis

Keyword(s):

Imaging Spectroscopy ◽

Reaction Intermediates ◽

Photoelectron Imaging ◽

Photoelectron Imaging Spectroscopy

Download Full-text

Lateral Adsorbate Interactions Inhibit HCOO- While Promoting CO Selectivity for CO2 Electrocatalysis on Ag

10.26434/chemrxiv.7182215.v1 ◽

2018 ◽

Author(s):

Divya Bohra ◽

Isis Ledezma-Yanez ◽

Guanna Li ◽

Wiebren De Jong ◽

Evgeny A. Pidko ◽

...

Keyword(s):

Electrochemical Reduction ◽

Experimental Approach ◽

Decisive Role ◽

Experimental Methods ◽

Reaction Intermediates ◽

Intermediate Species ◽

Experimental Knowledge ◽

Complex Interactions ◽

Ag Catalysts

The analysis presented in this manuscript helps bridge an important fundamental discrepancy between the existing theoretical and experimental knowledge regarding the performance of Ag catalysts for CO2 electrochemical reduction (CO2ER). The results demonstrate how the intermediate species *OCHO is formed readily en-route the HCOO– pathway and plays a decisive role in determining selectivity of a predominantly CO producing catalyst such as Ag. Our theoretical and experimental approach develops a better understanding of the nature of competition as well as the complex interactions between the reaction intermediates leading to CO, HCOO– and H2 during CO2ER. Details of computational and experimental methods are present in the Supporting Information provided.

Download Full-text