Solvent effect on the volume of activation and volume of the Diels–Alder reaction

Kiselev, V. D.; Коновалов, А. И.; Asano, Tsutomu; Kashaeva, E. A.; Iskhakova, G. G.; Shihab, Mahdi S.; Medvedeva, M. D.

doi:10.1002/poc.398

Cited by 32 publications

(6 citation statements)

References 12 publications

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“…This means that variations in the energy of nonspecific solvation and partial molar volume are determined by different factors. This conclusion is consistent with data of [6].…”

supporting

confidence: 95%

“…It was shown [6,10] that in the case of specific solute3sol-vent interactions the enthalpy of solvation clearly correlates with the change in the partial molar volume. However, as far as we compare the activation and reaction volumes for the Diels3Alder reactions involving the same dienophiles and different dienes (alkylbutadienes and cyclopentadiene, on the one hand, and substituted anthracenes, on the other hand), there are no specific interactions of the dienes with the solvent.…”

mentioning

confidence: 97%

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Influence of packing of the reactants and products in solution on the volume parameters of the Diels-Alder reaction

et al. 2004

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The possible causes of a dramatic difference in the volume parameters (by up to 153 20 cm 3 mol !1 ) of the Diels3Alder reactions involving bulky and small reactants are discussed. The partial molar volumes of anthracene and 9,10-dihydroanthracene and the heats of their solution in six solvents were determined.It is known [133] that the activation (DV ) and reaction (DV 0 ) volumes determined from the dependences of the rate (k) and equilibrium (K) constants on the external pressure [Eqs.(1), (2)] furnish additional information on the structure of the activated complex whose volume (V ) can be calculated withHere R is the universal gas constant; T, temperature; DG and DG 0 , activation and reaction Gibbs energies, respectively; and V reac , total molar volume of the reactants.The relationship between the molar volumes of the activated complex, reactants, and reaction products, and also the quantity q = DV /DV 0 allow better understanding of the reaction mechanism and the influence exerted by the reactants, catalysts, products, and reaction medium on the volume parameters of reactions [135].It is still unclear why the volume parameters of the nonpolar Diels3Alder reaction can dramatically change in a series of related reactants. As the molar volumes of diene3dienophile pairs increase, the absolute values of the volume parameters of the reactions considerably decrease [33 6]. For example, in the reactions of dienophiles with cyclopentadiene or alkylbutadienes, the activation and reaction volumes range from 335 to 3 40 cm 3 mol !1 , whereas in the reactions with anthracene derivatives these quantities are from 320 to 325 cm 3 mol !1 . There are no grounds to assume changes in the reaction mechanism in the series of related reactants. The significant difference in the volume parameters of the Diels3Alder reaction reflects the fact that the packing coefficients h (h = V W /V, where V W is the molar van der Waals volume) of bulkier reactants increase less significantly in going to the activated complex and then to the adduct. On the other hand, the packing coefficient is only a general characteristic of a substance in solution, bearing no information on factors responsible for changes in the partial molar volumes in going from one reactant to another or, for given reactants, from one solvent to another.Revealing the effect of solvation on variation of the molar volumes of the reactants, activated complex, and reaction products is one of the key steps in revealing the causes of changes in the reaction rates and equilibria at elevated pressures. The volume of a dilute solution can be described by Eq. (4).Here V A , V S , and V * S are the molar volumes of the solute, solvent in the bulk, and solvent in the solvation sphere; q is the number of solvent molecules in the solvation sphere; and N A and N S are the amounts (moles) of the solute and solvent, respectively. Hence, the partial molar volume of a solute (V A ) in a dilute solution is given byIn the absence of specific interactions in solution (V * S 3 V S = 0), the p...

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“…This means that variations in the energy of nonspecific solvation and partial molar volume are determined by different factors. This conclusion is consistent with data of [6].…”

supporting

confidence: 95%

mentioning

confidence: 97%

Influence of packing of the reactants and products in solution on the volume parameters of the Diels-Alder reaction

et al. 2004

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“…It has been shown that the measured data are in agreement with the assumption [11,14,31] that negative values of the activation volume in the retro-Diels-Alder reactions can be caused by different possibilities of penetration of the solvent molecules into large sterically hindered branched structures in the transition states and adduct. This corresponds to the fact that solvation of the substance is determined not only by the nature of intermolecular interactions, but also the probability of their realization (steric solvation effect).…”

Section: Discussionsupporting

confidence: 75%

“…It is well known [1,4,[9][10][11] that the rate of isopolar DAR is weakly dependent (if any) on the polarity of the medium. Only a strong donor-acceptor interaction, which is observed, for example, for π -acceptor tetracyanoethylene in the medium of π -donors (alkylbenzenes), significantly reduces the activity of dienophile and its rate in the direct reaction [4,[11][12][13][14]. However the reaction rates of the adduct 11 decomposition are insensitive to the properties of the solvent [11].…”

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confidence: 93%

Anomalies in the Change of Volumetric Parameters of the Diels–Alder Reaction in Solution

et al. 2012

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In this article negative values of the activation volume in retro-Diels-Alder reactions are interpreted in terms of the different possibilities of penetration of the solvent molecules into the sterically branched structures of the adduct and activated complex. Empty spaces, inaccessible to penetration of solvent molecules, lead to increases of the molar volume of the screened adducts in solution and, consequently, to a less negative value of the Diels-Alder reaction volume. The values of partial molar volumes of anthracene, maleic anhydride and the adducts cyclopentadiene-maleic anhydride, anthracene-maleic anhydride and anthracene-tetracyanoethylene, in several solvents, were calculated from the solution density data.

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“…Rate constants (k -1 /s -1 ) and the enthalpies (ΔH ≠ /kJ mol -1 ), entropies (ΔS ≠ /J mol -1 K -1 ), and volumes (ΔV ≠ /cm 3 mol -1 ) of activation of the decay of adduct 1 at different temperatures (T/K) in some solvents than that in inert solvents. 11 According to the data obtained (see Table 1), the rate constants and the parame ters of activation of the decay of adduct 1 in benzene and toluene do not differ from those in other solvents. The activation enthalpies of the decay of the adduct are higher by 20-30 kJ mol -1 than the balance between the energies of bond cleavage and bond formation in this reaction (66 kJ mol -1 ), which suggests a dominant contribution from the energy of σ bond cleavage in the adduct to the formation of an activation barrier.…”

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confidence: 82%

Energy and volume activation parameters of the retro-Diels—Alder reaction in different solvents

et al. 2009

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The temperature and pressure effects on the decay rate of an adduct obtained from 9 chloroanthracene and tetracyanoethene by a Diels-Alder reaction were studied. The rate constants (298.2 K) and the enthalpies, entropies, and volumes of activation were determined for the retro Diels-Alder reaction in different solvents. The data obtained confirm a possible decrease in the molar volume of the solvated adduct upon partial bond cleavage on the way to the transition state. The reversal of the sign in front of the activation volume cannot be indicative of a changed reaction mechanism.The kinetics of the forward Diels-Alder reaction is studied much better than that of its reverse. 1 The retro Diels-Alder reaction is characterized by high activation energies and usually low activation entropies. From data for the pressure effect on the rate of the forward Diels-Alder reaction it follows that the activation volume of the forward reaction can be more negative than the volume of the reaction itself. This requires the assumption that the transition state is more compact than the adduct. 2-4 Such a change in the volume profile of the reaction is difficult to explain for the Diels-Alder reaction, which is an isopolar process. It has been as sumed 1,5 that the solvent effects on the rate constant and activation parameters of the forward and retro DielsAlder reactions are due to a subtle differentiation between the solvation effects in the transition state.Subtle distinctions between the solvation effects are difficult to explain in terms of common solvent parameters. 6 One can assume that the transition state is differently accessible to different solvents during the solvation. If such unusual features of the solvation deter mine changes in the activation entropy and affect the partial molar volumes, then the activation volume should be expected to change in a nonmonotonic way. This vol ume is defined as a difference between the partial molar volumes of the transition state (V TS ) and the adduct (V 1 ):A decreased volume of an adduct upon its partial decomposition in the transition state is usually difficult to explain for an isopolar process. Considerable attention was focused on the accuracy of measurements. 7,8 Accord ing to the accumulated experimental data, the negative activation volumes appreciably exceed in absolute value the volumes for a large group of Diels-Alder reactions but do not for another group that is not smaller. 2-8 Nevertheless, the reliability of those data should be confirmed by independent direct measurements of acti vation volumes in retro Diels-Alder reactions. Only in two studies 5,9 devoted to the baric kinetics of the retro reaction was a slight volume reduction observed on the way from the adduct to the transition state. Because Diels-Alder adducts are sufficiently stable, the stock of suitable objects of investigation is limited. Considerable differences in the bond conjugation energy for reagents distinctly correlate with the reaction enthalpy, 1 which allows selection of convenient objects re...

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Solvent effect on the volume of activation and volume of the Diels–Alder reaction

Cited by 32 publications

References 12 publications

Influence of packing of the reactants and products in solution on the volume parameters of the Diels-Alder reaction

Influence of packing of the reactants and products in solution on the volume parameters of the Diels-Alder reaction

Anomalies in the Change of Volumetric Parameters of the Diels–Alder Reaction in Solution

Energy and volume activation parameters of the retro-Diels—Alder reaction in different solvents

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