Cyclization/Fission and Fragmentation/Recombination Mechanisms for the 1,2 Shift in Free Radicals:  A Computational Study of H2C•−CH2X (X = −C⋮CH, −C⋮N, −CHCH2, and −CHNH) and H2C•−CH2CYO (Y = −H, −F, −Cl, −CH3, −CN, −SH, −SCH3, −OH, and −O-)

George, Philip; Glusker, Jenny P.; Bock, Charles W.

doi:10.1021/jp001318g

Cited by 10 publications

(11 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…30,31 The above relation for k ∞ was calculated for each step at several temperatures and the values were then plotted as log k vs 1/T to obtain the corresponding Arrhenius rate parameters.…”

Section: Rate Constant Calculationsmentioning

confidence: 99%

Ring Expansion in Methylcyclopentadiene Radicals. Quantum Chemical and Kinetics Calculations

Dubnikova

Lifshitz

2002

J. Phys. Chem. A

View full text Add to dashboard Cite

Ring expansion processes in 1-, 2-, and 5-methylenecyclopentadiene radicals and isomerizations among the three isomers were studied by the Becke three-parameter hybrid method with Lee-Yang-Parr correlation functional approximation (B3LYP). Structure, energy, and frequency calculations were carried out with the Dunning correlation consistent polarized double (cc-pVDZ) and augmented aug-cc-pVDZ basis sets. The potential energy surfaces for ring expansion in methylenecyclopentadiene radicals consist of several intermediates and transition states. The process that takes place by insertion of the methylene group into the cyclopentadiene ring in the three isomers occurs via two principal mechanisms. One mechanism is associated with cleavage of the five-membered ring of the cyclopentadiene ring. In the second mechanism, the transition states of the first stage consist of a newly formed three-membered ring fused to the original cyclopentadiene ring. In all the three isomers of methylenecyclopentadiene, the reaction pathways leading to ring expansion include intermediates that via additional transition states lead to the production of the cyclohexadienyl radical. The latter, by a very fast H-atom ejection produces benzene. The structure and energetics of the various pathways are shown. The isomerization processes 1-methylenecyclopentadiene S 5-methylenecyclopentadiene and 2-methylenecyclopentadiene S 1-methylenecyclopentadiene involve a single 1,2-H atom shift and proceeds in one step without intermediates. The ring expansion in 1-methylenecyclopentadiene proceeds much faster via isomerization to 5-methylenecyclopentadiene than via direct formation of cyclohexadienyl.

show abstract

Section: Rate Constant Calculationsmentioning

confidence: 99%

Ring Expansion in Methylcyclopentadiene Radicals. Quantum Chemical and Kinetics Calculations

Dubnikova

Lifshitz

2002

J. Phys. Chem. A

View full text Add to dashboard Cite

show abstract

“…andλ # is the imaginary frequency of the reaction coordinate in cm −1 [30,31]. RRKM calculations corresponding to the pressure and temperature range of the experiments, with which the calculations were compared, had a negligible effect on the high pressure limit rate constant.…”

Section: Calculation Of Unimolecular Rate Constantsmentioning

confidence: 99%

Molecular hydrogen elimination from 2,5‐dihydrofuran, 2,3‐dihydrofuran, and 2‐methyl‐2,5‐dihydrofuran: Quantum chemical and kinetics calculations

Dubnikova¹,

Lifshitz²

2001

Int J of Chemical Kinetics

View full text Add to dashboard Cite

Density Function Theory calculations were carried out to evaluate the potential energy surfaces of H 2 elimination from 2,5-dihydrofuran, 2,3-dihydrofuran, and 2-methyl-2,5-dihydrofuran. The structure and energetics of the reactants, products, and transition states on the surfaces for all the three systems were determined and unimolecular rate constants for the H 2 elimination were calculated from transition state theory. The potential energy surfaces in 2,5-dihydrofuran and 2-methyl-2,5-dihydrofuran have each closed shell, 6-center transition state. The transition state for H 2 elimination from 2,3-dihydrofuran proceeds via two different pathways, both have barriers that are considerably higher than the barriers for H 2 elimination from 2,5-dihydrofuran and 2-methyl-2,5-dihydrofuran. One pathway proceeds via a 4-center transition state and one through a carbene intermediate. In all the cases the transition state leads to the formation of a H 2 -furan complex toward a complete separation to H 2 and furan. The calculated rate constants for 2,5-dihydrofuran and 2-methyl-2,5-dihydrofuran are in excellent agreement with the experimental observations. Owing to the very high barriers, the process in 2,3-dihydrofuran cannot compete with other reaction channels, such as isomerizations, and cannot be observed experimentally.

show abstract

“…This reaction mechanism has been first proposed as the homoallylic rearrangement by Montgomery et al in 1967 − for allylcarbinyl radical. The 1,2-vinyl migration is regarded as taking place by a two-step sequence: (1) ring closure of an allylcarbinyl radical to form a cyclopropylcarbinyl radical and (2) ring opening of the formed radical to yield an allylcarbinyl radical of rearranged structure. ,, Follow-up theoretical investigations revealed that this reaction mechanism could take place with quite low barrier heights. , For instance, George et al calculated that the barrier height of the 1,2-vinyl migration in 1-buten-4-yl radical is less than 10 kcal/mol …”

Section: Introductionmentioning

confidence: 99%

Kinetics of Homoallylic/Homobenzylic Rearrangement Reactions under Combustion Conditions

Wang

Zhang

2014

J. Phys. Chem. A

View full text Add to dashboard Cite

Homoallylic/homobenzylic radicals refer to typical radicals with the radical site located at the β position from the vinyl/phenyl group. These radicals are largely involved in combustion systems, such as the pyrolysis or oxidation of alkenes, cycloalkanes, and aromatics. The 1,2-vinyl/phenyl migration via two steps (cyclization/fission) is a peculiar reaction type for the homoallylic/homobenzylic radicals, entitled homoallylic/homobenzylic rearrangement, which has been studied by theoretical calculations including the Hirshfeld atomic charge analysis in the present work. With the help of rate constant calculations, the competition between this reaction channel and other possible pathways under combustion temperatures (500-2000 K) were evaluated. Analogous 1,3- and 1,4-vinyl/phenyl migration reactions for similar radicals with the radical sites located at the γ and δ positions from the vinyl/phenyl group were also computed. The results indicate that the 1,2-vinyl/phenyl migration is particularly important for the kinetics of unimolecular reactions of homoallylic radicals under 1500 K; nevertheless, it still has noticeable contribution at higher temperature. For those radicals with the radical site at the γ or δ positions, the respective 1,3- or 1,4-vinyl/phenyl migration channel plays an insignificant role under combustion conditions.

show abstract

Cyclization/Fission and Fragmentation/Recombination Mechanisms for the 1,2 Shift in Free Radicals: A Computational Study of H₂C^•−CH₂X (X = −C⋮CH, −C⋮N, −CHCH₂, and −CHNH) and H₂C^•−CH₂CYO (Y = −H, −F, −Cl, −CH₃, −CN, −SH, −SCH₃, −OH, and −O^-)

Cited by 10 publications

References 40 publications

Ring Expansion in Methylcyclopentadiene Radicals. Quantum Chemical and Kinetics Calculations

Ring Expansion in Methylcyclopentadiene Radicals. Quantum Chemical and Kinetics Calculations

Molecular hydrogen elimination from 2,5‐dihydrofuran, 2,3‐dihydrofuran, and 2‐methyl‐2,5‐dihydrofuran: Quantum chemical and kinetics calculations

Kinetics of Homoallylic/Homobenzylic Rearrangement Reactions under Combustion Conditions

Contact Info

Product

Resources

About