scholarly journals Direct SN2 or SN2X Manifold – Mechanistic Study of Ion-Pair Catalyzed Carbon(sp3)-Carbon(sp3) Bond Formation

2021 ◽  
Author(s):  
Richmond Lee ◽  
Chi Bong Eric Chao ◽  
Xu Ban ◽  
Siu Min Tan ◽  
Haibo Yu ◽  
...  
Keyword(s):  
Density Functional ◽  
Mechanistic Study ◽  
Functional Theory ◽  
Computational Screening ◽  
Reaction Barriers ◽  
Leaving Groups ◽  
Sn2 Pathway ◽  
Dft Modelling ◽  
Calculated Model ◽  
Oniom Calculations

Density functional theory (DFT) is used in this work to predict the mechanism for constructing congested quaternary-quaternary carbon(sp3)–carbon(sp3) bonds in a pentanidium catalyzed substitution reaction. Computational mechanistic studies were carried out to investigate the proposed SN2X manifold, which consists of two primary elementary steps: halogen atom transfer (XAT) and subsequent SN2. For the first calculated model on original experimental substrates, XAT reaction barriers were more kinetically competitive than an SN2 pathway and connects to thermodynamically stable intermediates. Extensive computational screening-modelling were then done on various substrate combinations designed to study steric influence and to understand the mechanistic rationale, and calculations reveal that sterically congested substrates prefer the SN2X manifold over SN2. Different halides as leaving groups were also screened and it was found that the reactivity increases in order of Br > Cl > F in agreement of the strength of C–X bonds. However, DFT modelling suggests that chlorides can be a viable substrate for the SN2X process which should be further explored experimentally. Finally, ONIOM calculations on the full catalyst model were carried out to rationalize the stereoselectivity which corroborates with experimental results.

scholarly journals Evidence of hydrogen trapping at second phase particles in zirconium alloys

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Christopher Jones ◽  
Vidur Tuli ◽  
Zaheen Shah ◽  
Mhairi Gass ◽  
Patrick A. Burr ◽  
...  
Keyword(s):  
Density Functional ◽  
Secondary Ion Mass Spectrometry ◽  
Zirconium Alloys ◽  
Nuclear Industry ◽  
Second Phase ◽  
Hydrogen Trapping ◽  
Functional Theory ◽  
Second Phase Particles ◽  
Hydrogen Isotope Ratios ◽  
Dft Modelling

AbstractZirconium alloys are used in safety–critical roles in the nuclear industry and their degradation due to ingress of hydrogen in service is a concern. In this work experimental evidence, supported by density functional theory modelling, shows that the α-Zr matrix surrounding second phase particles acts as a trapping site for hydrogen, which has not been previously reported in zirconium. This is unaccounted for in current models of hydrogen behaviour in Zr alloys and as such could impact development of these models. Zircaloy-2 and Zircaloy-4 samples were corroded at 350 °C in simulated pressurised water reactor coolant before being isotopically spiked with 2H2O in a second autoclave step. The distribution of 2H, Fe and Cr was characterised using nanoscale secondary ion mass spectrometry (NanoSIMS) and high-resolution energy dispersive X-ray spectroscopy. 2H− was found to be concentrated around second phase particles in the α-Zr lattice with peak hydrogen isotope ratios of 2H/1H = 0.018–0.082. DFT modelling confirms that the hydrogen thermodynamically favours sitting in the surrounding zirconium matrix rather than within the second phase particles. Knowledge of this trapping mechanism will inform the development of current understanding of zirconium alloy degradation through-life.

DENSITY FUNCTIONAL STUDY OF SELECTED MONO-ZINC AND GEM-DIZINC RADICAL CARBENOID CYCLOPROPANATION REACTIONS: OBSERVATION OF AN EFFICIENT RADICAL ZINC CARBENOID CYCLOPROPANATION REACTION AND THE INFLUENCE OF THE LEAVING GROUP ON RING CLOSURE

2003 ◽  
Vol 02 (03) ◽  
pp. 357-369 ◽  
Author(s):  
CUNYUAN ZHAO ◽  
DONG-QI WANG ◽  
DAVID LEE PHILLIPS
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Radical Reaction ◽  
Ring Closure ◽  
Functional Study ◽  
Reaction Step ◽  
Leaving Group ◽  
Reaction Barriers ◽  
Leaving Groups ◽  
Zinc Carbenoid

We report a theoretical study of the cyclopropanation reactions of EtZnCHI, (EtZn)2CH EtZnCHZnI, and EtZnCIZnI radicals with ethylene. The mono-zinc and gem-dizinc radical carbenoids can undergo cyclopropanation reactions with ethylene via a two-step reaction mechanism similar to that previously reported for the CH2I and IZnCH2 radicals. The barrier for the second reaction step (ring closure) was found to be highly dependent on the leaving group of the cyclopropanation reaction. In some cases, the (di)zinc carbenoid radical undergoes cyclopropanation via a low barrier of about 5–7 kcal/mol on the second reaction step and this is lower than the CH2I radical reaction which has a barrier of about 13.5 kcal/mol for the second reaction step. Our results suggest that in some cases, zinc radical carbenoid species have cyclopropanation reaction barriers that can be competitive with their related molecular Simmons-Smith carbenoid species reactions and produce somewhat different cyclopropanated products and leaving groups.

Theoretical elucidation of the energy conversion rate in organic photovoltaic cells of the fullerene nanostructure derivatives. A density functional theory study

2020 ◽  
Vol 19 (07) ◽  
pp. 2050025
Author(s):  
Nadjet Deddouche ◽  
Hafida Chemouri
Keyword(s):  
Density Functional Theory ◽  
Conversion Rate ◽  
Density Functional ◽  
Lithium Ion ◽  
Photovoltaic Cell ◽  
Energy Difference ◽  
Organic Photovoltaic ◽  
Mechanistic Study ◽  
Functional Theory ◽  
Kinetics Of

A comparative theoretical study of the kinetics of the Diels–Alder (DA) reaction between empty fullerene (C[Formula: see text]) and lithium ion encapsulated fullerene ([Formula: see text]) with 1,3 cyclohexadiene (C[Formula: see text]H[Formula: see text]) was carried out. This reaction takes place in a photovoltaic cell. The effect of the encapsulated [Formula: see text] ion on the conversion rate of solar energy into electricity has been highlighted through calculations based on the density functional theory (DFT). In addition, a static study using the global conceptual DFT indices, as part of the demonstration of the significant electrophilic power of the fullerene nanostructure, was carried out to show the effect of encapsulating the [Formula: see text] ion in this nanoparticle on the electrophilic power of Li[Formula: see text]@C[Formula: see text] and therefore on the acceleration of the reaction. The relationship between the HOMOdonor–LUMOacceptor energy difference and the DA reaction acceleration, and therefore the acceleration of light conversion (a rapid conversion implies a small gap), has been thoroughly examined. Moreover, a mechanistic study of the kinetics of the DA reaction of the fullerene involved in an organic photovoltaic cell has been carried out. In this section, a concerted synchronous mechanism with no effect of [Formula: see text] encapsulation on the synchronicity of the reaction was observed. Finally, it was revealed that Li[Formula: see text]@C[Formula: see text] reacted approximately 2466 times faster than C[Formula: see text]. Moreover, the experimental results were found in good agreement with the computer calculations.

Sign in / Sign up

Export Citation Format

Share Document