The orientation of free-radical addition to olefins (original) (raw)
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Journal of the Chemical Society, 1986
Ab mitio molecular orbital calculations of the transition states and barrier heights for the addition of atomic hydrogen to fluoroactylene and l,l-difluoroethylene are presented. The relative reactivity of these compounds and the regioselectivity of the addition reactions are analyzed in terms of chemically interpretable contributions by means of the energy decomposition scheme proposed by Morokuma. The usual PM0 approach of the problem is discussed in this context. A rationahzation of some of the experimental rules of radical reactivity is given.
Tetrahedron, 1980
We have recently written review articles which have summan 'sad 15 years of research work into the factors which control the rate and orientation of the addition of free radicals to olefins.' In these articles we emphasised that no simple property could be used to determine the orientation of free radical addition. Instead we showed that the rate and orientation of free radical addition to oleiins depend on "the complex interplay of polar, steric and bond-strength terms*','o Unfortunateiy this has Led some workers to fall back on more definite but incorrect hypotheses and it is the purpose of the present report to try and provide a quaNative theory which will sufIice for the majority of organic chemists.
Journal of Molecular Structure: THEOCHEM, 1999
Ab initio molecular orbital calculations of the barrier for the addition of gamma-substituted propyl radicals to various alkenes indicate that substituents at the gamma position of a radical can significantly affect the barrier. This finding supports recent experimental evidence for an enthalpic penultimate unit effect in free-radical copolymerization. For the reactions studied in the present work, this penultimate unit effect is consistent with a significant polar contribution. ᮊ
Journal of the American Chemical Society, 1994
High-level ab initio calculations at the QCISD/6-3 1 1G** + ZPVE level have been carried out to study the addition reactions of CHI', CHzOH', and CHzCN. radicals to the substituted alkenes C H 2 4 H X (X = H, NH2, F, C1, CHO, and CN) and the results analyzed with the aid of the curve-crossing model. We find that the reactivity of CH3* is primarily governed by enthalpy effects, whereas both enthalpy and polar effects are important for the reactions of CH20H' and CH2CN'. There is no general bamer height-enthalpy correlation for the latter two radicals because of the presence in some cases of polar effects that stabilize the transition states without a corresponding stabilization of the products. The polar effects are not sufficient, however, to significantly shift the location of the transition states, so a general structure-nthalpy correlation is observed.
Density Functional Theory Study of Addition Reactions of Carbon-Centered Radicals to Alkenes
The Journal of Physical Chemistry A, 2011
Addition reactions of carbon-centered radicals to unsaturated compounds have been studied using quantum chemistry. Following the review by Radom (Angew. Chem., Int. Ed. 2001, 40, 1340.), the radicals were grouped in four different families, and the alkenes were selected from among those typical of polymer productions. All of the kinetic constants were calculated using density functional theory and classic transition state theory. Geometries of reactants, products, and transition states were determined at the B3LYP/6-311+G(d,p) level of theory, whereas reaction enthalpies, activation energies, and kinetic constants were estimated using different basis sets. By comparative evaluation of the results obtained with different basis sets, the best computational approach for each kinetic step was identified. As a result of this study, a computational methodology suitable for investigating a large number of kinetic pathways typical of freeradical polymerization processes is proposed.
Journal of Fluorine Chemistry, 1997
The two-step synthesis of the diols is based on the radical addition of 2,2-dimethyl-1,3-dioxolane (1), a protected ethane-1,2-diol, to per¯uoroalk-1-4±6) with preparative yields above 90% in each step. The additions were initiated photochemically or by dibenzoyl peroxide and were completely chemoselective and almost completely regioselective. 4-Fluoroalkylated dioxolanes obtained (7±11) were deprotected by acid methanolysis to afford 1-poly¯uoroalkylethane-1,2-diols (12±16). 1,3-Dioxolane (27) or 2,2,4-trimethyl-1,3-dioxolane (30) reacted at two centers to yield regioisomeric mixtures of¯uoroalkylated dioxolanes. The factors in¯uencing¯uoroole®n and dioxolane regioselectivity are discussed. #
Kinetics of the Radical-Chain Addition to Double Molecular Bonds — The Low-Reactive Free Radicals Shortening the Kinetic Chains , 2014
ABSTRACT Five reaction schemes are suggested for the initiated nonbranched-chain addition of free radicals to the multiple bonds of the unsaturated compounds. The proposed schemes include the reaction competing with chain propagation reactions through a reactive free radical. The chain evolution stage in these schemes involves three or four types of free radicals. One of them is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the suggested schemes, nine rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. These equations provide good fits for the nonmonotonic (peaking) dependences of the formation rates of the molecular products (1:1 adducts) on the concentration of the unsaturated component in binary systems consisting of a saturated component (hydrocarbon, alcohol, etc.) and an unsaturated component (olefin, allyl alcohol, formaldehyde, or dioxygen). The unsaturated compound in these systems is both a reactant and an autoinhibitor generating low-reactive free radicals. A similar kinetic description is applicable to the nonbranched-chain process of the free-radical hydrogen oxidation, in which the oxygen with the increase of its concentration begins to act as an oxidation autoingibitor (or an antioxidant). The energetics of the key radical-molecule reactions is considered. Key words: Binary system, unsaturated compound, low-reactive radical, autoinhibitor, competing reaction, non-branched-chain addition, kinetic equation, rate, parameters, thermochemical data, energy.
Journal of Applied Solution Chemistry and Modeling, 2014
Five reaction schemes are suggested for the initiated nonbranched-chain addition of free radicals to the multiple bonds of the unsaturated compounds. The proposed schemes include the reaction competing with chain propagation reactions through a reactive free radical. The chain evolution stage in these schemes involves three or four types of free radicals. One of them is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the suggested schemes, nine rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. These equations provide good fits for the nonmonotonic (peaking) dependences of the formation rates of the molecular products (1:1 adducts) on the concentration of the unsaturated component in binary systems consisting of a saturated component (hydrocarbon, alcohol, etc.) and an unsaturated component (olefin, allyl alcohol, formaldehyde, or dioxygen). The unsaturated compound in these systems is both a reactant and an autoinhibitor generating low-reactive free radicals. A similar kinetic description is applicable to the nonbranched-chain process of the free-radical hydrogen oxidation, in which the oxygen with the increase of its concentration begins to act as an oxidation autoingibitor (or an antioxidant). The energetics of the key radical-molecule reactions is considered. Keywords: Binary System, Unsaturated Compound, Low-Reactive Radical, Autoinhibitor, Competing Reaction, Non-Branched-Chain Addition, Kinetic Equation, Rate, Parameters, Thermochemical Data, Energy.
A note on the transition state of radical addition reactions
Chemical Physics Letters, 1978
An ab initio MO study of the reaction of F-atoms and CHj radicals with ethylene indicates that the transition state oc curs later in the F-atom reaction and that there is considerable charge polarization in the aIkene arising mainly from transfer of a p electron to fluorine. 1. Evidence of an early transition state
Kinetics of Free-Radical Nonbranched-Chain Addition to Alkenes and Their Derivatives
International Journal of Innovative Studies in Sciences and Engineering Technology (IJISSET) , 2017
The reaction scheme is suggested for the initiated nonbranched-chain addition of free radicals to the double bonds of the unsaturated compounds. The proposed scheme includes the reaction competing with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves three types of free radicals. One of them is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the suggested scheme, four rate equations (containing one to three parameters to be determined directly) are deduced using quasi-steady-state treatment. These equations provide good fits for the nonmonotonic (peaking) dependences of the formation rates of the molecular products (1:1 adducts) on the concentration of the unsaturated component in binary systems consisting of a saturated component (hydrocarbon, alcohol, etc.) and an unsaturated component (alkene, allyl alcohol, etc.). The unsaturated compound in these systems is both a reactant and an autoinhibitor generating low-reactive free radicals. The energetics of the key radical-molecule reactions is considered. Keywords: Binary System, Unsaturated Compound, Low-Reactive Radical, Autoinhibitor, Competing Reaction, Nonbranched-Chain Addition, Kinetic Equation, Rate, Parameters, Thermochemical Data, Energy.