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.

scholarly journals Experimental and Theoretical Study of the Silicon-Hydrogen Bond Activation by Rhodium Dicarbonyl Complex in Solution

2019 ◽  
Vol 2 (2) ◽  
pp. 121
Author(s):  
Agus Abhi Purwoko ◽  
Saprizal Hadisaputra ◽  
Alistair J. Less
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Bond Activation ◽  
Theoretical Study ◽  
Functional Study ◽  
Intramolecular Rearrangement ◽  
Intensity Increase ◽  
Activation Product ◽  
Complex Product ◽  
Parent Complex

The photoreactivity of hydrotris-(3,5-dimethylpyrazolyl)boratedicarbonylrhodium(I) or HB(Pz*)3Rh(CO)2 complex has been studied at room-temperature n-pentane solution in the presence of 0.05 M Et3SiH (Et = C2H5). The IR spectra show that the decline of νCO parent complex at 1980 and 2054 cm-1 is followed by growing bands at 2029 and 2020 cm-1. In light of the photolysis of the parent complex in neat n-pentane solution the feature at 2020 cm-1 is tentatively assigned to the νCO band of the Si-H bond activation product. Upon standing in the dark, the 2020 cm-1 increases slightly in contrast with the 2029 cm-1 peak which decreases over time. These observations raise question whether the intensity increase of the 2020 cm-1 peak occurs unimolecularly resulting from the intramolecular rearrangement of the C-H bond activation of Et3SiH or bimolecularly as a result of the elimination of the C-H bond activation of the solvent and subsequent re-addition of the Si-H bond of the Et3SiH ligand. To gain more insight to reaction dynamics of the Si-H bond activation, the experimental results are compared to the photolysis of the parent complex in neat Et3SiH. The quantum efficiency (ϕSi-H) of this photoreaction yields a low value of 0.16. The results indicate that the Si-H bond activation is facilitated by intramolecular rearrangement mode. In addition, a theoretical study was conducted using density functional study at B3LYP/LanL2DZ level of theory, and the findings implicate that the final complex product was produced by the Si-H bond activation of Et3SiH.

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 Theoretical Study of the H-+CH3Cl SN2 Reaction

1979 ◽  
Vol 32 (10) ◽  
pp. 2289 ◽  
Author(s):  
ER Talaty ◽  
JJ Woods ◽  
G Simons
Keyword(s):  
Ab Initio ◽  
Theoretical Study ◽  
Reaction Path ◽  
Planar Structure ◽  
Sn2 Reaction ◽  
Leaving Group ◽  
Leaving Groups

A theoretical study of the C3v reaction path of the H- + CH3Cl → CH4+Cl- SN2 reaction with the use of the GAUSSIAN 70 program reveals an earlier departure of the leaving group than in other ab initio studies of similar reactions involving poorer leaving groups, and predicts an intermediate planar structure that is highly ionic and which should be represented as a tight ion triplet, H-[CH3+]Cl-.

Formation of Ring A in the Biosynthesis of Hopanoids from Squalene. A Density Functional Study

2004 ◽  
Vol 69 (1) ◽  
pp. 261-266 ◽  
Author(s):  
B. Andes Hess
Keyword(s):  
Activation Energy ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Ring Closure ◽  
Functional Study ◽  
Chair Conformer ◽  
Density Functional Study ◽  
Concerted Reaction

Density functional calculations were carried out on the ring closure of the 2,6-dimethyloct-6-en-2-yl cation to a chair conformer of the 1,2,3,3-tetramethylcyclohexyl cation as a model for the first step in the biosynthetic cyclization of squalene to the triterpene hopanoids. The concerted reaction was found to have an activation energy of 4.6 kcal/mol and to be exothermic by 11.5 kcal/mol.

The effect of steric size of leaving group on rates of the competing syn- and anti-pathways in biomolecular elimination

1980 ◽  
Vol 45 (8) ◽  
pp. 2171-2178
Author(s):  
Jiří Závada ◽  
Magdalena Pánková
Keyword(s):  
Comparative Analysis ◽  
Homologous Series ◽  
Leaving Group ◽  
Leaving Groups

Approximate rates of the competing syn- and anti-pathways have been determined in t-C4H9OK-t-C4H9OH promoted elimination from two homologous series of tosylates: I-OTs trans-III (R = H, CH3, C2H5, n-C3H7, i-C3H7, t-C4H9) and II-OTs trans-IV (R = CH3, C2H5, n-C3H7, i-C3H7, t-C4H9). A comparison has been made with rates of the same processes in the (+) elimination of the corresponding trimethylammonium salts I-N(CH3)3 trans-III and (+) II-N(CH3)3 trans-IV. The title effect is demonstrated by a comparative analysis of the rate patterns obtained for the two leaving groups.

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