scholarly journals A computational study of the influence of methyl substituents on competitive ring closure to α- and β-lactones

2017 ◽  
Vol 15 (34) ◽  
pp. 7235-7240 ◽  
Author(s):  
Philippe B. Wilson ◽  
Ian H. Williams
Keyword(s):  
Computational Study ◽  
Ring Closure

gem-Dimethyl substitution at C3 enhances the preference for β-lactone formation from 2-chlorosuccinate but methylation at C2 almost favours α-lactone.

scholarly journals Isomerization and Fragmentation Reactions on the [C2SH4] Potential Energy Surface. The Metastable Thione-S-Methylide Isomer

2020 ◽  
Author(s):  
Zoi Salta ◽  
Marc E. Segovia ◽  
Aline Katz ◽  
Nicola Tasinato ◽  
Vincenzo Barone ◽  
...  
Keyword(s):  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surface ◽  
Density Functional ◽  
Energy Surface ◽  
Computational Study ◽  
Experimental Information ◽  
Reaction Scheme ◽  
Ring Closure ◽  
Complete Analysis

Thione S-methylide (TSM), the parent species of the thiocarbonyl ylide family, is a 1,3-dipolar, planar species on the [C2SH4] potential energy surface (PES), which has not shared the richness of studies dedicated to its isomers, the cyclic thiirane (THI), and the keto-enol pair vinyl thiol (VTH)/thioacetaldehyde (THA). While the conrotatory ring closure reaction toward THI was studied in the ‘90s, no complete analysis of the PES is available in the literature. In the present paper, we report a computational study of the reaction scheme linking all species on that PES. We employ several levels of calculation, ranging from density functional theory (DFT), through CCSD(T) based composite schemes, to CASSCF/CASPT2 multi-reference procedures, to find the best description of TSM, its isomers, and the transition states (TSs) ruling their interconversion. Fragmentation of TSM, THA and THI were investigated and compared to the available experimental information. We found that the B2PLYP-D3 functional, contrary to M06-2XD3 or B97X-D, describes well the geometry of both TSM and the transition state connecting it to THI. The reverse barrier, from THI to TSM, amounts to 52.2 kcal mol-1 (to be compared to 17.6 kcal mol-1 for the direct one), thus explaining why, in general, thiocarbonyl ylides cannot be prepared from thiiranes. Conversion of THI to VTH implies also a large barrier, explaining why the reaction has been observed only at high temperatures. The fragmentation of THI to S(3P) or S(1D) and ethylene was also explored, together with the decomposition to H2S plus acetylene. Open species, both in triplet and singlet states, were identified as intermediates in the fragmentations, and their energies were found to be lower than the transition state for the isomerization of THI to VTH, thus explaining the preference for fragmentation over isomerization at relatively low temperatures.

scholarly journals Observation of a Tricyclic[4.1.0.02,4]heptane During a Michael Addition-Ring Closure Reaction and a Computational Study on Its Mechanism of Formation

2017 ◽  
Vol 82 (23) ◽  
pp. 12511-12519 ◽  
Author(s):  
Marco Farren-Dai ◽  
John R. Thompson ◽  
Anna Bernardi ◽  
Cinzia Colombo ◽  
Andrew J. Bennet
Keyword(s):  
Michael Addition ◽  
Computational Study ◽  
Ring Closure ◽  
Mechanism Of Formation

scholarly journals Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

2017 ◽  
Vol 13 ◽  
pp. 410-416 ◽  
Author(s):  
Michael L McKee ◽  
Grzegorz Mlostoń ◽  
Katarzyna Urbaniak ◽  
Heinz Heimgartner
Keyword(s):  
Computational Methods ◽  
Computational Study ◽  
Heavy Atom ◽  
Ring Closure ◽  
Reactive Intermediate

An intriguing stepwise diradical mechanism of the dimerization of the reactive intermediate (thiocarbonyl S-methanide) appearing in the reaction of phenyl selenophen-2-yl thioketone with diazomethane was studied by means of computational methods. The preferred formation of the unusual macroheterocycle, competitive with the 1,3-ring closure leading to a thiirane and the head-to-head dimerization yielding a 1,4-dithiane derivative, respectively, was explained based on the analysis of the structure of the favored conformer of the intermediate, delocalized diradical species. The influence of selenium as a ‘heavy atom’ for stabilization of this intermediate has been emphasized.

The Walden cycle revisited: a computational study of competitive ring closure to α- and β-lactones

2006 ◽  
pp. 1106 ◽  
Author(s):  
J. Grant Buchanan ◽  
Richard A. Diggle ◽  
Giuseppe D. Ruggiero ◽  
Ian H. Williams
Keyword(s):  
Computational Study ◽  
Ring Closure

scholarly journals Isomerization and Fragmentation Reactions on the [C2SH4] Potential Energy Surface. The Metastable Thione-S-Methylide Isomer

2020 ◽  
Author(s):  
Zoi Salta ◽  
Marc E. Segovia ◽  
Aline Katz ◽  
Nicola Tasinato ◽  
Vincenzo Barone ◽  
...  
Keyword(s):  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surface ◽  
Density Functional ◽  
Energy Surface ◽  
Computational Study ◽  
Experimental Information ◽  
Reaction Scheme ◽  
Ring Closure ◽  
Complete Analysis

Thione S-methylide (TSM), the parent species of the thiocarbonyl ylide family, is a 1,3-dipolar, planar species on the [C2SH4] potential energy surface (PES), which has not shared the richness of studies dedicated to its isomers, the cyclic thiirane (THI), and the keto-enol pair vinyl thiol (VTH)/thioacetaldehyde (THA). While the conrotatory ring closure reaction toward THI was studied in the ‘90s, no complete analysis of the PES is available in the literature. In the present paper, we report a computational study of the reaction scheme linking all species on that PES. We employ several levels of calculation, ranging from density functional theory (DFT), through CCSD(T) based composite schemes, to CASSCF/CASPT2 multi-reference procedures, to find the best description of TSM, its isomers, and the transition states (TSs) ruling their interconversion. Fragmentation of TSM, THA and THI were investigated and compared to the available experimental information. We found that the B2PLYP-D3 functional, contrary to M06-2XD3 or B97X-D, describes well the geometry of both TSM and the transition state connecting it to THI. The reverse barrier, from THI to TSM, amounts to 52.2 kcal mol-1 (to be compared to 17.6 kcal mol-1 for the direct one), thus explaining why, in general, thiocarbonyl ylides cannot be prepared from thiiranes. Conversion of THI to VTH implies also a large barrier, explaining why the reaction has been observed only at high temperatures. The fragmentation of THI to S(3P) or S(1D) and ethylene was also explored, together with the decomposition to H2S plus acetylene. Open species, both in triplet and singlet states, were identified as intermediates in the fragmentations, and their energies were found to be lower than the transition state for the isomerization of THI to VTH, thus explaining the preference for fragmentation over isomerization at relatively low temperatures.

The effect of leaving radical on the formation of tetrahydroselenophene by SHi ring closure: an experimental and computational study

2015 ◽  
Vol 13 (8) ◽  
pp. 2310-2316 ◽  
Author(s):  
Amber N. Hancock ◽  
Sofia Lobachevsky ◽  
Naomi L. Haworth ◽  
Michelle L. Coote ◽  
Carl H. Schiesser
Keyword(s):  
Kinetic Parameters ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Computational Study ◽  
Kinetic Studies ◽  
Laser Flash ◽  
Ring Closure ◽  
Computational Techniques ◽  
High Level

Competition kinetic studies augmented with laser-flash photolysis and high-level computational techniques [G3(MP2)-RAD], with [COSMO-RS, SMD] and without solvent correction, provide kinetic parameters for the ring closures of a series of 4-(alkylseleno)butyl radicals.

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