Theoretical Studies on the CH 3 CO + Cl Reaction: Hydrogen Abstraction versus CO Displacement (original) (raw)
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Theoretical Investigation of Cheletroptic Decarbonylation Reactions
Journal of Chemical Theory and Computation, 2006
In this study, B3LYP is used to calculate the decarbonylation reactions of the bicyclo-[2.2.1]hepta-2,5-dien-7-one (7-norbornadienone, 1) and its related extended fused aromatic analogues 2-5. On the basis of our results, all of the reactions tend to proceed synchronously to expel CO, forming the corresponding aromatic hydrocarbons. It is found that the more exothermic the reaction is, the less of a reaction barrier it needs to overcome. Moreover, upon a decrease of the reaction exothermicity, the structure of the transition state is farther away from the reactant, and the reaction barrier increases. The results agree well with the Hammond postulate as well as the Bell-Evans-Polanyi principle. Studies predict an activation energy of 27.83 kcal/mol for 5, so that the production of pentacene from compound 5 might proceed at elevated temperatures such as 400 K.
Kinetics and Thermochemistry of the Reaction of 1-Chloroethyl Radical with Molecular Oxygen
The Journal of Physical Chemistry, 1995
The kinetics of the reaction CH3CHC1+ 0 2 F?. CH3CHC102products (1) has been studied at temperatures 296-839 K and He densities of (3-49) x 10l6 molecule cm-3 by laser photolysis/photoionization mass spectrometry. Rate constants were determined in time-resolved experiments as a function of temperature and bath gas density. At low temperatures (298-400 K) the rate constants are in the falloff region under the conditions of the experiments. Relaxation to equilibrium in the addition step of the reaction was monitored within the temperature range 520-590 K. Equilibrium constants were determined as a function of temperature and used to obtain the enthalpy and entropy of the addition step of the reaction (1). At high temperatures (750-839 K) the reaction rate constant is independent of both pressure and temperature within the uncertainty of the experimental data and equal to (1.2 f 0.4) x cm3 molecule-' s-'. Vinyl chloride (C2H3C1) was detected as a major product of reaction 1 at T = 800 K. The rate constant of the reaction CH3CHC1 + C12 products (6) was determined at room temperature and He densities of (9-36) x 10l6 molecule cm-3 using the same technique. The value obtained is k6 = (4.37 f 0.69) x cm3 molecule-' s-'. An estimate of the high-pressure limit for reaction 1 was determined using this measured k6 and the kl/k6 ratio obtained by Kaiser et al.:l k"1 (T=298K) = (1.04 f 0.22) x lo-" cm3 molecule-' s-'. In a theoretical part of the study, structure, vibrational frequencies, and energies of nine conformations of CH3CHC102 were calculated using ab initio UHF/6-31G* and MP2/6-31G** methods. The theoretical results are used to calculate the entropy change of the addition reaction As0298 =-152.3 f 3.3 J mol-' K-'. Th~s entropy change combined with the experimentally determined equilibrium constants resulted in a CH3CHC1-02 bond energy m 2 9 8 =-131.2 f 1.8 kJ mol-l. The rooq-temperature entropy (S O 2 9 8 = 341.0 f 3.3 J mol-' K-') and the heat of formation (A H f o~9 8 =-54.7 f 3.7 kJ mol-') of the CH3CHC102 adduct were obtained.
Theoretical models for mechanism and catalysis in carbonyl addition
Journal of the American Chemical Society, 1980
Exploration of potential energy curves, calculated by ab initio procedures at the STO-3G and 4-31G levels, for the systems H 2 0 + CH20, HO-+ CH20, and H 2 0 + CH20H+ produces models for enforced concertedness of proton transfer and heavy-atom reorganization (in the H20 + CHzO reaction) and specific-acid-base catalysis (in the two ion-molecule reactions).
International Journal of Chemical Kinetics, 2016
Thermal decomposition kinetics of dicyclopentadiene-1,8-dione 7 implied an intramolecular competition between α,βand β,γ-double bond to assist the CO elimination. Experimental thermolysis of 7 in dioxane gave 3a,7a-dihydro-1H-inden-1-one (cisbicyclo[4.3.0]nona-2,4,7-triene-9-one), CO gas, and a very small amount of indanone. This result suggested β,γ-double bond favored the extrusion of CO gas. Calculations of several density functional theory (DFT) levels of theory and CBS-QB3 method were employed. Two mechanisms were considered: a one-step concerted pathway and a stepwise mechanism involving [1,3] and [1,5] hydrogen sigmatropic migrations. The CAM-B3LYP/6-31G(d,p) calculation reasonably agrees with the experimental kinetic parameters. The mechanism appears to be unimolecular in one step concerted through a five-membered cyclic transition state. Isomerization of product cis-bicyclo[4.3.0]nona-2,4,7-triene-9-one yielding 1-indanone is presented and described. Calculation from substrate 7 may explain in a similar way the mechanism of decomposition of compounds 1-6. The present work may well promote to the possibility of carrying out experimental research works on the thermal decarbonylation kinetics in a liquid solution and in the gas phase of β,γ-unsaturated aliphatic ketones.
Combined crossed beam and theoretical studies of the C(1D) + CH4 reaction
The Journal of Chemical Physics, 2013
The reaction involving atomic carbon in its first electronically excited state 1 D and methane has been investigated in crossed molecular beam experiments at a collision energy of 25.3 kJ mol −1 . Electronic structure calculations of the underlying potential energy surface (PES) and Rice-Ramsperger-Kassel-Marcus (RRKM) estimates of rates and branching ratios have been performed to assist the interpretation of the experimental results. The reaction proceeds via insertion of C( 1 D) into one of the C-H bonds of methane leading to the formation of the intermediate HCCH 3 (methylcarbene or ethylidene), which either decomposes directly into the products C 2 H 3 + H or C 2 H 2 + H 2 or isomerizes to the more stable ethylene, which in turn dissociates into C 2 H 3 + H or H 2 CC + H 2 . The experimental results indicate that the H-displacement and H 2 -elimination channels are of equal importance and that for both channels the reaction mechanism is controlled by the presence of a bound intermediate, the lifetime of which is comparable to its rotational period. On the contrary, RRKM estimates predict a very short lifetime for the insertion intermediate and the dominance of the H-displacement channel. It is concluded that the reaction C( 1 D) + CH 4 cannot be described statistically and a dynamical treatment is necessary to understand its mechanism. Possibly, nonadiabatic effects are responsible for the discrepancies, as triplet and singlet PES of methylcarbene cross each other and intersystem crossing is possible. Similarities with the photodissociation of ethylene and with the related reactions N( 2 D) + CH 4 , O( 1 D) + CH 4 and S( 1 D) + CH 4 are also commented on.
Theoretical investigation of the photochemical reaction mechanism of cyclopropenone decarbonylation
Molecular Physics, 2011
The gas-phase decomposition mechanism of the photochemical and thermal reaction of cyclopropenone leading to carbon monoxide and acetylene has been investigated theoretically. We employed the B3LYP, MP2, and CASSCF methods with the 6-311 + G** basis set to determine the pathways and the potential energy surface (PES) of this reaction. PES minima were characterized by the absence of any imaginary frequencies and compared with the transition states that contained single imaginary frequencies. The intrinsic reaction coordinate (IRC) method was used to find the minimum energy paths in which reactants and products were connected to the transition states. Activation barrier, thermodynamic, and IRC analyses were performed using the above three methods. Our computations indicated that the decomposition of cyclopropenone proceeds through a stepwise mechanism containing two transition states (TS1 and TS2) and an intermediate. The results show that TS1, the critical transition state, determines the rate of the cyclopropenone decomposition reaction. Therefore, we employed natural bond order (NBO) calculations to probe the structure of the intermediate. The calculations showed that the intermediate has resonance structures containing a carbene and a zwitterion. Our results are in good agreement with previous theoretical and experimental studies. © 2011 Taylor & Francis.
Kinetics and thermodynamics of intra- and intermolecular carbon-hydrogen bond activation
Journal of the American Chemical Society, 1985
The preference for intra-and intermolecular C-H bond activation has been determined by equilibration of the complex (C5Me5)Rh(PMe2CH2C6H5)(C6H5)H and its cyclometalated analogue (C5Me5)Rh(PMe,CH2C6H4)H in neat benzene at 51.2 OC ( K , = 36.7, AGO = -2.32 kcal/mol). By monitoring the approach to equilibrium over a 40 O C temperature range, the difference between the activation parameters for intra-and intermolecular activation by the 16-electron intermediate [(C5Me5)Rh(PMe2CH2C6HS)1 can be obtained (intra-inter): AAH' = 1.7 f 0.8 kcal/mol; AAS' = 4.5 f 2.5 eu. At 25 OC, this corresponds to a 1.86:l kinetic preference for intermolecular activation of the neat benzene solvent by the coordinatively unsaturated intermediate [(C5Me5)Rh(PMe2CH2C6H5)] over intramolecular cycloaddition. The effect of solvent concentration on activation selectivity is discussed. A comparison with intra-and intermolecular alkane activation is made by equilibrating the complex (C5Me5)Rh(PMezCH2CH2CH2)H with benzene and by examining the kinetics of cyclometalation vs. alkane activation. These studies reveal the same general trend with regard to thermodynamic and kinetic selectivity in alkanes and arenes: while there is little kinetic selectivity between intra-and intermolecular reactions involving neat solvent, there is a moderate thermodynamic preference for the intramolecular activation. . The activation of carbon-hydrogen bonds by homogeneous transition-metal complexes is a topic that has received a great deal of attention recently. Much of this interest arises from the recent reports that indicate that even the C-H bonds of alkanes can 0002-7863/85/1507-0620$01.50/0 (1) (a) Crabtree, R. H.; Mihelcic, J. M.; Quirk, J. M. J. Am. Chem. SOC. 1979, 101, 7738-7740. Crabtree, R. H.; Mellea, M. F.; Mihelcic, J. M.; Quirk, J. M. J. Am. Chem. SOC. 1982, 104, 107-113. Crabtree, R. H.; Demou, P. C.; Eden, D.; Mihelcic, J. M.; Parnell, C. A.; Quirk, J. M.; Morris, G. E. J. Am. Chem. SOC. 1982,104,6994-7001. (b) Baudry, D.; Ephritikhine, M.; Felkin, H. J . Chem. Soc., Chem. Commun. 1980, 1243-1244. Baudry, D.; Ephritikhine, M.; Felkin, H.; Zakrzewski, J.
Journal of Computational Chemistry, 2018
Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12// B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH 2 with ketene CH 2 CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice-Ramsperger-Kassel-Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH 3 and C 2 H 4 + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C 2 H 4 + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH 2 COCH 2 intermediate or along the pathway of CO elimination from the initial CH 2 CH 2 CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C 2 H 4 + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH 3 CHCO and cyclic CH 2 COCH 2 intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300-3000 K, which are proposed for kinetic modeling of ketene reactions in combustion.
The Journal of Physical Chemistry A, 2017
The synergetic use of bonding evolution theory (BET) and non−covalent interaction (NCI) analysis allows to obtain new insight into the bond breaking/forming processes and electron redistribution along the reaction path to understand the molecular mechanism of a reaction and recognize regions of strong and weak electron pairing. This viewpoint has been considered for cheletropic extrusion of CO from unsaturated cyclic ketones cyclohepta−3,5−dien−1−one CHD, cyclopent−3−en−1−one CPE and bicyclo[2.2.1]hept−2−en−7−one BCH by using hybrid functional MPWB1K in conjugation with aug−cc−pVTZ basis set. Decarbonylation of CHD, CPE and BCH are non-polar cyclo−elimination reactions which are characterized by the sequence of turning points (TPs) as: CHD: 1-11-C[CC]C † C † FFF TS C † C † C †-0: HT + CO, CPE: