Symmetry

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9 pages, 2879 KiB

Open AccessArticle

Computational Insight into the Rope-Skipping Isomerization of Diarylether Cyclophanes

by Thomas J. Summers, Hrishikesh Tupkar, Tyler M. Ozvat, Zoë Tregillus, Kenneth A. Miller and Nathan J. DeYonker

Symmetry 2021, 13(11), 2127; https://doi.org/10.3390/sym13112127 - 9 Nov 2021

Cited by 1 | Viewed by 1936

Abstract

The restricted rotation of chemical bonds may lead to the formation of stable, conformationally chiral molecules. While the asymmetry in chiral molecules is generally observed in the presence of one or more stereocenters, asymmetry exhibited by conformational chirality in compounds lacking stereocenters, called [...] Read more.

The restricted rotation of chemical bonds may lead to the formation of stable, conformationally chiral molecules. While the asymmetry in chiral molecules is generally observed in the presence of one or more stereocenters, asymmetry exhibited by conformational chirality in compounds lacking stereocenters, called atropisomerism, depends on structural and temperature factors that are still not fully understood. This atropisomerism is observed in natural diarylether heptanoids where the length of the intramolecular tether constrains the compounds to isolable enantiomers at room temperature. In this work, we examine the impact tether length has on the activation free energies to isomerization of a diarylether cyclophane substructure with a tether ranging from 6 to 14 carbons. Racemization activation energies are observed to decay from 48 kcal/mol for a 7-carbon tether to 9.2 kcal/mol for a 14-carbon tether. Synthetic efforts to experimentally test these constraints are also presented. This work will likely guide the design and synthesis of novel asymmetric cyclophanes that will be of interest in the catalysis community given the importance of atropisomeric ligands in the field of asymmetric catalysis. Full article

(This article belongs to the Special Issue Advances in Theoretical and Computational Chemistry)

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14 pages, 4586 KiB

Open AccessArticle

Investigation of Pharmaceutical Importance of 2H-Pyran-2-One Analogues via Computational Approaches

by Samata E. Shetgaonkar, Shiva Prasad Kollur, Renjith Raveendran Pillai, Karthick Thangavel, Sanja J. Armaković, Stevan Armaković, Chandan Shivamallu, Raghavendra G. Amachawadi, Asad Syed, Abdallah M. Elgorban, Ali H. Bahkali and Fateh V Singh

Symmetry 2021, 13(9), 1619; https://doi.org/10.3390/sym13091619 - 3 Sep 2021

Cited by 2 | Viewed by 2310

Abstract

Highly functionalized spirocyclic ketals were synthesized through asymmetric oxidative spirocyclization via carbanion-induced ring transformation of 2H-pyran-2-ones with 1,4-cyclohexandione monoethyleneketal under alkaline conditions. Further acidic-hydrolysis of obtained spirocyclic ketals yields highly substituted 2-tetralone in good yield. Computational analysis based on the DFT [...] Read more.

Highly functionalized spirocyclic ketals were synthesized through asymmetric oxidative spirocyclization via carbanion-induced ring transformation of 2H-pyran-2-ones with 1,4-cyclohexandione monoethyleneketal under alkaline conditions. Further acidic-hydrolysis of obtained spirocyclic ketals yields highly substituted 2-tetralone in good yield. Computational analysis based on the DFT calculations and MD simulations has been performed in order to predict and understand global and local reactivity properties of newly synthesized derivatives. DFT calculations covered fundamental reactivity descriptors such as molecular electrostatic potential and average local ionization energies. Nitrogen atom and benzene rings have been recognized as the most important molecular sites from these aspects. Additionally, to predict whether studied compounds are stable towards the autoxidation mechanism, we have also studied the bond dissociation energies for hydrogen abstraction and identified the derivative which might form potentially genotoxic impurities. Interactions with water, including both global and local aspects, have been covered thanks to the MD simulations and calculations of interaction energies with water, counting of formed hydrogen interactions, and radial distribution functions. MD simulations were also used to identify which excipient could be used together with these compounds, and it has been established that the polyvinylpyrrolidone polymer could be highly compatible with these compounds, from the aspect of calculated solubility parameters. Full article

(This article belongs to the Special Issue Advances in Theoretical and Computational Chemistry)

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21 pages, 5198 KiB

Open AccessArticle

Diffusion-Limited Reaction Kinetics of a Reactant with Square Reactive Patches on a Plane

by Changsun Eun

Symmetry 2020, 12(10), 1744; https://doi.org/10.3390/sym12101744 - 21 Oct 2020

Cited by 1 | Viewed by 2353

Abstract

We present a simple reaction model to study the influence of the size, number, and spatial arrangement of reactive patches on a reactant placed on a plane. Specifically, we consider a reactant whose surface has an N × N square grid structure, with [...] Read more.

We present a simple reaction model to study the influence of the size, number, and spatial arrangement of reactive patches on a reactant placed on a plane. Specifically, we consider a reactant whose surface has an N × N square grid structure, with each square cell (or patch) being chemically reactive or inert for partner reactant molecules approaching the cell via diffusion. We calculate the rate constant for various cases with different reactive N × N square patterns using the finite element method. For N = 2, 3, we determine the reaction kinetics of all possible reactive patterns in the absence and presence of periodic boundary conditions, and from the analysis, we find that the dependences of the kinetics on the size, number, and spatial arrangement are similar to those observed in reactive patches on a sphere. Furthermore, using square reactant models, we present a method to significantly increase the rate constant by sequentially breaking the patches into smaller patches and arranging them symmetrically. Interestingly, we find that a reactant with a symmetric patch distribution has a power–law relation between the rate constant and the number of reactive patches and show that this works well when the total reactive area is much less than the total surface area of the reactant. Since our N × N discrete models enable us to examine all possible reactive cases completely, they provide a solid understanding of the surface reaction kinetics, which would be helpful for understanding the fundamental aspects of the competitions between reactive patches arising in real applications. Full article

(This article belongs to the Special Issue Advances in Theoretical and Computational Chemistry)

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