Conformations and Barriers of Haloethyl Radicals (CH<sub>2</sub>XCH<sub>2</sub>, X = F, Cl, Br, I):  Ab Initio Studies

Ihee, Hyotcherl; Zewail, and Ahmed H.; Goddard, William A.

doi:10.1021/jp990867n

Cited by 50 publications

(57 citation statements)

References 69 publications

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“…Our higher theoretical level estimate for the rotational barrier [QCISD(T)/aug-cc-pVDZ//QCISD/6-31G(d,p)] is 2.1 kcal/mol (see Table 2). Furthermore, data in Tables 2-5 show that our computed barrier lies between 1.8 [MP2/6-311++G(3df,3pd)] and 3.1 kcal/mol [Becke3LYP/6-31G(d,p)], lower than the ESR estimated value and in good agreement with those of Ihee et al 28 V. 1,2 Hydrogen Shift. The most stable form of the chloroethyl radical is the 1-chloroethyl radical (see Tables 2-5).…”

Section: Table 1: Most Significant Geometrical Parameters As Computedsupporting

confidence: 87%

“…47 Engels et al 23 computed (MRD-CI) a value (without optimization of the transition structure) of 4.3 kcal/mol while the MP4/6-311G-(d,p)//MP2/6-31G(d) barrier is 2.1 kcal/mol. 48 Ihee et al 28 reported the values 1.8 (LMP2) and 3.5 (Becke3LYP) kcal/mol. Our higher theoretical level estimate for the rotational barrier [QCISD(T)/aug-cc-pVDZ//QCISD/6-31G(d,p)] is 2.1 kcal/mol (see Table 2).…”

Section: Table 1: Most Significant Geometrical Parameters As Computedmentioning

confidence: 99%

“…Their PMP4/6-31G(d,p)//UMP2/6-31G(d,p) calculations indicate that there is no transition structure on the two possible pathways (symmetric and unsymmetric). Calculations of Ihee et al 28 [local MP2 and DFT using the LAV3P relativistic effective core potential 29 for describing the chlorine atom and the 6-31G(d,p) basis set for hydrogen and carbon atoms] seem to confirm the Skell hypothesis of symmetric bridging 24 (they locate a symmetrically bridged structure 10.5 kcal/mol below the dissociation limit at the Becke3LYP level of theory) to explain the stereochemical control of haloethyl radicals, concluding that bridged structures play an important role in the dissociation processes involving the CH 2 ClCH 2 • radical.…”

Section: Introductionmentioning

confidence: 95%

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Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

et al. 2000

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The potential energy surface of the reaction between chlorine atom and ethylene was explored at the MP2/ 6-31G(d,p), Becke3LYP/6-31G(d,p), QCISD/6-31G(d,p), MP2/6-311+G(d,p), MP2/6-311++G(3df,3pd), and MP2/aug-cc-pVDZ levels of theory. Further QCISD(T)/6-31G(d,p) and QCISD(T)/cc-pVDZ optimizations were performed for some structures of special interest. The geometrical parameters computed for the different structures located on the potential energy surface do not differ too much when employing different methods and basis sets with the only exceptions of those structures involving long distance interactions (van der Waals structures). The pronounced flatness of the potential energy surface in the regions where these structures appear seems to be the responsible for the observed discrepancies. The full optimized QCISD structures tend to become less stable than those computed at the MP2 level, whereas the opposite is true for the Becke3LYP structures. At the MP2 and QCISD levels, the transition structure associated with a direct shuttle motion in the addition channel is too high in energy to be involved in the dissociation mechanism. The existence of two bridged structures Iadd (minimum) and TSadd (transition structure) on the potential energy surface helps to explain the experimentally detected stereochemical control exercised by the chlorine atom in reactions involving haloethyl radicals. Contrarily, the Becke3LYP calculations suggest a mechanism in which the direct shuttle motion could play a relevant role, although the competing mechanism of rotation around the C-C bond is lower in energy. The MP2 and QCISD abstraction channels also differ considerably from the Becke3LYP one. However, in this case all the different potential energy surfaces seem to be consistent with the reported experimental data on the activation energy and endothermicity for the abstraction reaction. The QCISD(T)/ aug-cc-pVDZ//QCISD/6-31G(d,p) relative energies and barrier heights are consistent with the experimental data available on exo/endothermicities and activation barriers for the addition and abstraction reactions.

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Section: Table 1: Most Significant Geometrical Parameters As Computedsupporting

confidence: 87%

Section: Table 1: Most Significant Geometrical Parameters As Computedmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

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Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

et al. 2000

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“…41,48,49 Moreover, recent computational investigations show that B3LYP calculations describe quite well the behavior of internal bond rotation of open-shell chemical species. 50,51 Thus, we examined the rotational energy profiles of the substituted methyl radicals by using B3LYP 42 and QCISD(T) 43 calculations. The values of µ and η were calculated according to three-point approximation, namely eqs 2a and 2b.…”

Section: Computational Detailsmentioning

confidence: 99%

Internal Bond Rotation in Substituted Methyl Radicals, H₂B−CH₂, H₃C−CH₂, H₂N−CH₂, and HO−CH₂: Hardness Profiles

Uchimaru¹,

Chandra²,

Kawahara³

et al. 2001

J. Phys. Chem. A

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The energy profiles for the internal bond rotation of substituted methyl radicals, X-CH 2 (X ) BH 2 , CH 3 , NH 2 , and OH) were examined with B3LYP/6-31G(d) calculations. Energy evaluation of each point along the rotational coordinate was also carried out with single-point calculation at the computational levels of B3LYP/ 6-311+G(2df,p) and QCISD(T)/6-311+G(2df,p). The computed rotational energy profiles, as well as the calculated values for the geometrical parameters, the vibrational frequencies, and the ionization potential, were in reasonable agreement with previously reported experimental and theoretical results. Except for H 3 C-CH 2 radical, the profiles of chemical potential and hardness along the rotational coordinates present striking contrast to those expected from the corollary of the principle of maximum hardness. Thus, there seems to be no rigorous reason for hardness to be minimum in the transition state region, in general.

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“…EPR and X-ray crystallographic data for several coenzyme B 12 -dependent systems indicate that intermediate free radicals are bound some distance from cob(II)alamin (e.g., 6.5 in glutamate mutase [5]). It is therefore expected that the barrier to rotation about the s-bond between the methylidene Catom bearing the radical and the adjacent C-atom in the product-related radical for all coenzyme B 12 -dependent C-skeleton rearrangements will be relatively low (n.b., there is essentially free rotation in the ethyl radical [6]) and hardly perturbed by the Co-atom of cob(II)alamin.…”

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confidence: 99%

Stereochemistry of the Methyl Group in (R)-3-Methylitaconate Derived by Rearrangement of 2-Methylideneglutarate Catalysed by a Coenzyme B12-Dependent Mutase

Ciceri

Pierik

Hartrampf

et al. 2000

HCA

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Dedicated to Professor Albert Eschenmoser on the occasion of his 75th birthday 2-Methylideneglutarate mutase is an adenosylcobalamin (coenzyme B 12 )-dependent enzyme that catalyses the equilibration of 2-methylideneglutarate with (R)-3-methylitaconate. This reaction is believed to occur via protein-bound free radicals derived from substrate and product. The stereochemistry of the formation of the methyl group of 3-methylitaconate has been probed using a chiral methyl group. The methyl group in 3-([ 2 H 1 , 3 H]methyl)itaconate derived from either (R)-or (S)-2-methylidene[3-2 H 1 ,3-3 H 1 ]glutarate was a 50 : 50 mixture of (R)-and (S)-forms. It is concluded that the barrier to rotation about the CÀC bond between the methylene radical centre and adjacent C-atom in the product-related radical [ . CH 2 CH( À O 2 CCCH 2 )CO 2 À ] is relatively low, and that the interaction of the radical with cob(II)alamin is minimal. Hence, cob(II)alamin is a spectator of the molecular rearrangement of the substrate radical to product radical.

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Conformations and Barriers of Haloethyl Radicals (CH₂XCH₂, X = F, Cl, Br, I): Ab Initio Studies

Cited by 50 publications

References 69 publications

Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

Internal Bond Rotation in Substituted Methyl Radicals, H₂B−CH₂, H₃C−CH₂, H₂N−CH₂, and HO−CH₂: Hardness Profiles

Stereochemistry of the Methyl Group in (R)-3-Methylitaconate Derived by Rearrangement of 2-Methylideneglutarate Catalysed by a Coenzyme B12-Dependent Mutase

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Conformations and Barriers of Haloethyl Radicals (CH2XCH2, X = F, Cl, Br, I): Ab Initio Studies

Cited by 50 publications

References 69 publications

Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

Internal Bond Rotation in Substituted Methyl Radicals, H2B−CH2, H3C−CH2, H2N−CH2, and HO−CH2: Hardness Profiles

Stereochemistry of the Methyl Group in (R)-3-Methylitaconate Derived by Rearrangement of 2-Methylideneglutarate Catalysed by a Coenzyme B12-Dependent Mutase

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Conformations and Barriers of Haloethyl Radicals (CH₂XCH₂, X = F, Cl, Br, I): Ab Initio Studies

Internal Bond Rotation in Substituted Methyl Radicals, H₂B−CH₂, H₃C−CH₂, H₂N−CH₂, and HO−CH₂: Hardness Profiles