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Volumn 21, Issue 9, 2008, Pages 758-782

Comparison of mechanistic models for correlation of activation energies of liquid-phase addition of carbon-centered radicals to terminal olefins

Author keywords

Enthalpy effects; Mechanistic models; Polar effects; Radical addition; Thermochemical properties of radicals

Indexed keywords

ACTIVATION ENERGY; ENTHALPY; KETONES; LIQUID PHASE EPITAXY; OLEFINS; REACTION KINETICS; THERMODYNAMICS;

EID: 49749144951     PISSN: 08943230     EISSN: 10991395     Source Type: Journal    
DOI: 10.1002/poc.1375     Document Type: Article
Times cited : (15)

References (168)
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    • Recent computational evidence suggests that this preference also has an electronic component; for example, Reference [3
    • Recent computational evidence suggests that this preference also has an electronic component; for example, Reference [3].
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    • Computational approaches to rate constants are making steady progress towards chemical accuracy but are still method and basis set dependent. M. K. Sabbe, A. G. Vandeputte, M.-F. Reyniers, V. Van Speybroeck, M. Waroquier, G. B. Marin, J. Phys. Chem. A 2007, 111, 8416.
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    • A few kinetic studies involved optical detection of radical decay or CIDNP development in a radical disproportionation product
    • A few kinetic studies involved optical detection of radical decay or CIDNP development in a radical disproportionation product.
  • 30
    • 49749127656 scopus 로고    scopus 로고
    • Since only terminal olefins were considered, steric effects were assumed to be trivial. Of course, the deduced systematic variation of A with radical structure may be considered to be at least partly 'steric' in origin (References [6] and [35]).
    • Since only terminal olefins were considered, steric effects were assumed to be trivial. Of course, the deduced systematic variation of A with radical structure may be considered to be at least partly 'steric' in origin (References [6] and [35]).
  • 31
    • 49749137398 scopus 로고    scopus 로고
    • For the very rapid reactions of the highly nucleophilic POH with electron-deficient olefins, k approached or even exceeded the assigned A; these E values were set at zero.
    • For the very rapid reactions of the highly nucleophilic POH with electron-deficient olefins, k approached or even exceeded the assigned A; these E values were set at zero.
  • 32
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    • There is some evidence for modest acceleration by increased solvent polarity for additions which have a large polar effect. For example, a 2.75-fold increase in k (ΔE, 0.6 kcal mol-1 for constant A) was reported for the highly nucleophilic-electrophilic pair 1-(diethylamino)ethyl radical and methyl acrylate in going from hexane to acetonitrile (or methanol/acetonitrile 20:80, J. Lalevee, X. Allonas, J. P. Fouassier, D. Rinaldi, M. F. Ruiz Lopez, J. L. Rivail, Chem. Phys. Lett. 2005, 415, 202
    • -1 for constant A) was reported for the highly nucleophilic-electrophilic pair 1-(diethylamino)ethyl radical and methyl acrylate in going from hexane to acetonitrile (or methanol/acetonitrile (20:80)); J. Lalevee, X. Allonas, J. P. Fouassier, D. Rinaldi, M. F. Ruiz Lopez, J. L. Rivail, Chem. Phys. Lett. 2005, 415, 202.
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    • 2; D. P. Curran, E. Eichenberger, M. Collis, M. G. Roepel, G. Thoma, J. Am. Chem. Soc. 1994, 116, 4279.
  • 36
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    • Additional kinetic data for which X and Y are both functional groups are not included because of a lack of data for the correlating variables for these more complex olefins
    • Additional kinetic data for which X and Y are both functional groups are not included because of a lack of data for the correlating variables for these more complex olefins.
  • 40
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    • -1 slightly dependent on the olefin.
    • -1 slightly dependent on the olefin.
  • 44
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    • All thermochemical quantities used herein refer to gas-phase standard-state values at 298 K.
    • All thermochemical quantities used herein refer to gas-phase standard-state values at 298 K.
  • 45
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    • The underlying assumption in this dissection is that there is negligible effect of substituents on the γ-carbon on the stability of RCH 2Xr, that is, D(RCH2CXY-H, DMeCH2CXY-H
    • 2CXY-H).
  • 46
    • 49749137889 scopus 로고    scopus 로고
    • Of course, this is fundamentally the same information because the dissociation enthalpy (D) values implicitly contain ΔfH values for radicals and their stable precursors
    • fH values for radicals and their stable precursors.
  • 48
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    • We have restricted ourselves to experimental data; computational values are still rather method-dependent, particularly for radicals; for example, E. I. Izgorodina, D. R. B. Brittain, J. L. Hodgson, E. H. Krenske, C. Y. Lin, M. Namazian, M. L Coote, J. Phys. Chem. A 2007, 111, 10754
    • We have restricted ourselves to experimental data; computational values are still rather method-dependent, particularly for radicals; for example, E. I. Izgorodina, D. R. B. Brittain, J. L. Hodgson, E. H. Krenske, C. Y. Lin, M. Namazian, M. L Coote, J. Phys. Chem. A 2007, 111, 10754.
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    • Eds.: PJ. Linstrom, W.G. Mallard, NIST Chemistry Webbook, NIST Standard Reference Database Number 69, http://webbook.nist.gov; National Institute of Standards and Technology, Gaithersburg, MD, June, 2005.
    • (2005) NIST Chemistry Webbook, NIST Standard Reference Database Number 69
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    • S. G. Lias, J. E. Bartmess, J. F. Liebman, J. L. Holmes, R. D. Levin, W. G. Mallard, J. Phys. Chem. Ref. Data 1988, 17, Supplement No. (1).
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  • 64
    • 49749100437 scopus 로고    scopus 로고
    • The compiled value (Reference [47, of D for CH3CH(-H)CH=O of 91.7 is derived from early measurements of ΔacidH(R-H) for propionaldehyde (366.4, Reference [65, and the EA(R) from its enolate (38.9, Reference [66, The revised acidity (365.2, Reference [50, would reduce this value to 90.5. However, individual EA(R) values of 37.3 and 40.0 have more recently been reported from the (E) and (Z) enolates, respectively, generated stereoselectively (References [67,68, EA(R) measurements for the enolate formed by gas-phase deprotonation of propionaldehyde (References [69,70, suggest that it is the (E) isomer (References [67,68, If its EA(R) is then the appropriate one to use, D(R-H) would be reduced further to 88.9 (91.6 for the other EA(R, However, several factors engender skepticism concerning this low value. First, recent computational evidence suggests that the (Z) isomer of the radical is 0.5-0.7 more stable than the (E) isomer
    • acidH(R-H) for propionaldehyde (366.4, Reference [65]), and the EA(R) from its enolate (38.9, Reference [66]). The revised acidity (365.2, Reference [50]) would reduce this value to 90.5. However, individual EA(R) values of 37.3 and 40.0 have more recently been reported from the (E) and (Z) enolates, respectively, generated stereoselectively (References [67,68]). EA(R) measurements for the enolate formed by gas-phase deprotonation of propionaldehyde (References [69,70]) suggest that it is the (E) isomer (References [67,68]). If its EA(R) is then the appropriate one to use, D(R-H) would be reduced further to 88.9 (91.6 for the other EA(R)). However, several factors engender skepticism concerning this low value. First, recent computational evidence suggests that the (Z) isomer of the radical is 0.5-0.7 more stable than the (E) isomer (References [71,72]), and the individual EA(R) values would then place the (Z) enolate 3.4 lower in energy than the (E) enolate. Since the lowest energy conformer of pro-pionaldehyde has the methyl group and the carbonyl oxygen in the (Z)-like geometry (Reference [73]), this stability ordering would indicate that its deprotonation is contrathermodynamic. Second, the ΔD(R-H) = 5.4 value between propionaldehyde and acetaldehyde would be atypically large (as in footnote d of Table 2). Third, one does not know what mixture of radical isomers is formed in radical addition to acrolein.
  • 97
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    • There is still be some confusion between vertical and adiabatic values in the various sources; the NIST compilation Reference [50, appears to consciously list, or adjust to, adiabatic values
    • There is still be some confusion between vertical and adiabatic values in the various sources; the NIST compilation (Reference [50]) appears to consciously list, or adjust to, adiabatic values.
  • 121
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    • Denisov (References [122-125]) has applied intersecting parabola models to deduce changes in transition state geometries from experimental values of E and ΔH. These models in principle offer a circuitous iterative route to derive E from ΔH, but the required inputs include the distance and the force constant of the forming bond, quantities that can only be obtained from computations or from previously derived empirical correlations based on paired E and ΔH data.
    • Denisov (References [122-125]) has applied intersecting parabola models to deduce changes in transition state geometries from experimental values of E and ΔH. These models in principle offer a circuitous iterative route to derive E from ΔH, but the required inputs include the distance and the force constant of the forming bond, quantities that can only be obtained from computations or from previously derived empirical correlations based on paired E and ΔH data.
  • 134
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    • Updated values were taken from R. A. Jackson, M. Sharifi, J. Chem. Soc. Perkin Trans. 2 1996, 775.
    • Updated values were taken from R. A. Jackson, M. Sharifi, J. Chem. Soc. Perkin Trans. 2 1996, 775.
  • 135
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    • This treatment makes the common assumption that the σ values are still applicable when X and Y are directly substituted on the reaction center without the intervening p-phenylene group which is integral to their definition; cf. Y-.W. Wu, H.-T. Huang, Z.-J. Huang, H.-M. Huang, J.-F. Yang, Tetrahedron 2005, 61, 4461
    • This treatment makes the common assumption that the σ values are still applicable when X and Y are directly substituted on the reaction center without the intervening p-phenylene group which is integral to their definition; cf. Y-.W. Wu, H.-T. Huang, Z.-J. Huang, H.-M. Huang, J.-F. Yang, Tetrahedron 2005, 61, 4461.
  • 138
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    • 2 for the Evans-Polanyi plots with our updated values of E and ΔH(R,X,Y) are typically lower than those reported by FR with the use of their values (as described below). It also appears that FR excluded the points for the phenyl-substituted olefins H,Ph, Me,Ph, and Ph,Ph in many of their individual correlations.
    • 2 for the Evans-Polanyi plots with our updated values of E and ΔH(R,X,Y) are typically lower than those reported by FR with the use of their values (as described below). It also appears that FR excluded the points for the phenyl-substituted olefins H,Ph, Me,Ph, and Ph,Ph in many of their individual correlations.
  • 139
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    • 2 value but a negative slope. It also gave the only negative Evans-Polanyi slope.
    • 2 value but a negative slope. It also gave the only negative Evans-Polanyi slope.
  • 143
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  • 152
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    • For another rather 'non-conventional' additive method that relies on empirically optimized parameters and computational input, refer A. V. Sokolov, Int. J. Quant. Chem. 2002, 88, 358.
    • For another rather 'non-conventional' additive method that relies on empirically optimized parameters and computational input, refer A. V. Sokolov, Int. J. Quant. Chem. 2002, 88, 358.
  • 155
    • 49749126371 scopus 로고    scopus 로고
    • polar in the Parr-Pearson treatment refers to an A:B acid-base complex at its equilibrium bond distance, whereas we are attempting to estimate the polar stabilization at a transition state distance.
    • polar in the Parr-Pearson treatment refers to an A:B acid-base complex at its equilibrium bond distance, whereas we are attempting to estimate the polar stabilization at a transition state distance.
  • 156
    • 49749092100 scopus 로고    scopus 로고
    • As the equations are formulated, a positive value of S corresponds to electron transfer from the radical to the olefin
    • As the equations are formulated, a positive value of S corresponds to electron transfer from the radical to the olefin.
  • 160
    • 49749088746 scopus 로고    scopus 로고
    • In our pragmatic 'optimization' process, a large number of quartets of Cn, Ce, γn, and γe values were generated randomly and independently in ranges around the trial values, that is, with no restrictions on their ratios, and (ΔE)av and sd(ΔE) were evaluated for each. The most promising quartets from this random screening were further fine-tuned until an optimum quartet emerged. While we cannot guarantee that an even broader search might not reveal an even better optimum, we believe this protocol gives a reliable route to approach the absolute optimum closely
    • av and sd(ΔE) were evaluated for each. The most promising quartets from this random screening were further fine-tuned until an optimum quartet emerged. While we cannot guarantee that an even broader search might not reveal an even better optimum, we believe this protocol gives a reliable route to approach the absolute optimum closely.
  • 162
    • 49749094044 scopus 로고    scopus 로고
    • Reference [60] and references therein
    • Reference [60] and references therein.
  • 163
    • 49749096416 scopus 로고    scopus 로고
    • This treatment assumes that delocalization will affect C and γ similarly, and it makes no provision for 'special' values for the phenylated cases
    • This treatment assumes that delocalization will affect C and γ similarly, and it makes no provision for 'special' values for the phenylated cases.
  • 164
    • 49749088926 scopus 로고    scopus 로고
    • Assume that the fraction of spin delocalization of magnitude(1-g) is accompanied by a fractional modulation of C* or γ* of magnitude of (1 - f); let h be the ratio (1 - f)/(1 - g); then f = [1 +h(g - 1)].
    • Assume that the fraction of spin delocalization of magnitude(1-g) is accompanied by a fractional modulation of C* or γ* of magnitude of (1 - f); let h be the ratio (1 - f)/(1 - g); then f = [1 +h(g - 1)].
  • 165
    • 49749141471 scopus 로고    scopus 로고
    • Values of for methylene or methine hydrogens cannot be used because they are strongly affected by preferred rotational conformations
    • Values of for methylene or methine hydrogens cannot be used because they are strongly affected by preferred rotational conformations.
  • 166
    • 49749139376 scopus 로고    scopus 로고
    • Although hetero-atom substituents offer the potential for aαH to be perturbed by non-planarity at the radical center, the radicals MOH, RCH2CHOEt, RCH2CHOAc, and RCH 2CHCI all fit well on the reported relationships between and DR-H, Reference 162
    • 2CHCI all fit well on the reported relationships between and D(R-H) (Reference 162).
  • 168
    • 49749115237 scopus 로고    scopus 로고
    • Olefin held at unity, as well as the inverse case. Both results fell approximately half-way between those of rows 3 and 5.
    • Olefin held at unity, as well as the inverse case. Both results fell approximately half-way between those of rows 3 and 5.


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