Cyclopentene rate constants

Bennet, P.J., Harris, S.J., Kerr, J. A. (1987) A reinvestigation of the rate constants for the reactions of ozone with cyclopentene and cyclohexene under atmospheric conditions. Int. J. Chem. Kinet. 19, 609-614. 

Rogers, J.D. (1989) Rate constant measurements for the reaction of the hydroxyl radical with cyclohexene, cyclopentene, and glutaraldehyde. Environ. Sci. Technol. 23, 177-181. 

Franzen34 photolyzed CH2N2-butadiene mixtures in the pressure range 31-335 mm., with butadiene in excess by a factor of 2-15. Franzen also observed cyclopentene as a product, the ratio of cyclopentene to vinyl cyclopropane decreasing from 0.25 at 35 mm. to 0.095 at 335 mm. Franzen proposed that some of the cyclopentene resulted from 1,4 addition of methylene to butadiene, on the grounds that all excited vinyl-cyclopropane should be collisionally deactivated at pressures as high as 335 mm. However, the ratio of cyclopentene to vinylcyclopropane obtained by Franzen at 335 mm. is close to that predicted by the ratio of rate constants for reactions (63) and (64) calculated by Frey.44... 

When one attempts to extend these empirical correlations once again, now considering rate constants for vinylcyclopropane to cyclopentene rearrangements, a fair linear correlation is obtained (Figure 4). The correlation line has an intercept of 56.7 kcal mol 1 and a slope of 0.690 (R2 = 0.99). The rate constants utilized were corrected for symmetry (a factor of 1/2 for vinylcyclopropane, and of 1/4 for 1,1-dicyclopropylethene) and the radical stabilization energies of-CH2CR=CH2 for R=Me or cyclopropyl were taken to be identical. The rate constants for vinylcyclopropane to cyclopentene rearrangements respond... 

In the case of ethylene itself the cyclopentene technique is obviously inapplicable and the relative rate constants have in this case been obtained in other ways, for example, by measuring yield of carbon monoxide formed by fragmentation of the products of reaction of oxygen atoms with ethylene. In this case the total pressure has to be kept approximately constant although some variation is not too important in view of the relatively small effect of pressure on CO yield at pressures normally used. 

Second-order rate constants for the oxidation of cyclopropenes with 3-chloroperoxybenzoic acid in carbon tetrachloride at 0 "C were in the order 1,2-diphenyl- (3.4), 3-methyl-l, 2-diphenyl-(1.24), 3,3-dimethyl-l,2-diphenyl- (0.4), 1,2,3-triphenyleyelopropene (0.122). The rates are somewhat lower than those of the corresponding 3-substituted cyclopentenes. On this scale, the relative rates of reaction of 1,2-diphenylcyclobutene and cyclopentene are 3.3 and 38.8. " ... 

A minor product (corresponding to about 0-5 % of the cyclopentene peak) was detected which had the same retention time as methylenecyclo-butane. At pressures below 3 mm the rate constant decreased with pressure and fell to approximately one half of the high-pressure value at 0-07 mm. The results obtained could be fitted by the Kassel equation by assuming that the reactant had eighteen effective oscillators. The data are thus consistent with the isomerization being a truly unimolecular transformation. On the basis both of the observed energy of activation and thermochemical data and of estimates of bond strengths, these... 

It was shown by Ortiz de Montellano et al. that bicyclo[2.1.0]pentane was oxidized by rat liver microsomes to a 7 1 mixture of e <7o-2-hydroxy-bicyclo[2.1.0]pentane and 3-cyclopenten-l-ol, consistent with a radical ring-opening reaction. Applications of the radical-clock method by Ingold and by Newcomb began to measure the lifetime of the suspected radical cage intermediate. The rate constant for the rearrangement of bicyclo[2.1.0]pent-2-yl radical to 3-cyclopenten-... 

Room temperature rate constants and Arrhenius parameters for the gas-phase reactions of ozone with cw-2-butene, 2-methyl-2-butene and a number of cycloalkenes are shown in Table 1 together with the literature values. The rate coefficients for cw-2-butene and 2-methyl-2-butene are in excellent agreement with the data evaluation of Atkinson and Carter [3]. The reported room temperature rate constants for the reaction of ozone with cyclopentene and cyclohexene show a considerable degree of scatter. The present results for cyclopentene provide support for the recent determinations by Bennett et al [24], Nolting et al [25], and Green and Atkinson [21], while the value for cycloheptene is slightly lower than the reported values [20] and [25]. No previous kinetic studies have been carried out on the reactions of O3 with cw-cyclooctene and cw-cyclodecene. 

Rate constants for the reaction of O3 with a number of substituted cycloalkenes were also determined in this work. From the results, the magnitude of the rate constant depends on the nature of the substituent and its position on the ring. As expected, substitution of a hydrogen atom attached at the 1 position in cyclopentene by an electron-withdrawing chlorine atom decreases the reactivity for reaction with the electrophilic ozone molecule. This would appear to be due to both a decrease in the pre-exponential factor and an increase in activation energy. 

In an attempt to determine whether peracid oxidation of cyclopropenes to enones proceeds by ct- or ic-bond oxidation, Friedrich and Fiato compared the second-order rate constant for allylically substituted cyclopropenes and cyclopentenes. The results (Table 1) indicate rather small allylic substitution effects in the cyclopentenes, but larger rate reductions in the cyclopropenes. The magnitude of the effect is not in line with an epoxidation-type transition state and may be more consistent with o attack, but insufficient background data are available to allow firm conclusions from these results. A comparison of oxidation rates of 1,2-diphenyl-cyclopropene, -cyclobutene, and -cyclopentene yielded data which were much more consistent with oxabicyclobutane formation, as did an examination of substituent effects at the vinylic positions in cyclopropene. ... 

The rate constants (lO k /l " min ) for bromination of cyclopentene, cyclohexene, and cis-cyclo-octene are 37.5, 6.84, and 0.73 the corresponding values for the 1,2-dimethyl derivatives are 17300, 2080, and 730, The bromination rates for 1-methylcyclohexene, 1-methyl-cis-cyclo-octene, 1-ethylcyclopentene, and 1-ethyl-... 

The concentration of ethylene and the calculated concentration of allyl radical were employed in the reaction mechanism postulated in the preceeding section to estimate the overall rate constants of the reactions of allyl radical with ethylene to produce both cyclopentene and 1-pentene, Experimental rates of formations of cyclopentene and 1-pentene were of course also used in these calculations. ... 

The direct reaction is first-order in the concentrations of the metal complex and the olefin and the second-order rate constant depends on the nature of olefin, as indicated by some of the data in Table S.9. Strain in the olefin appears to increase its reactivity, as shown for norbomene and cyclopentene. There may be some steric effects of olefin substituents, but these effects may be attenuated by better electron donation from the substituents. It was found also that the reaction rate with 2,3-dimethyl-2-butene was insensitive to the polarity of the solvent, with relative values of 1 0.6 0.8 in cyclohexane. Tiff and methanol, respectively. This seems to rule out an ionic or polar transition state or intermediate, and the authors favor a concerted cycloaddition mechanism. 

Table 4.1 Rate data and rate constants for the hydroboration of cyclopentene (0.400 M) and cyclohexene (0.400 M) with (O-BBNy (0.200 M) in carbon tetrachloride at 25 C [ 1 ]...

LiBr and in the presence of cyclopentene as a scavenger olefin. The kinetics, determined by monitoring the formation of strong acids (TfOH or HBr), show that the rate of solvolysis of 65 is dependent on [Br-] (at a constant ionic strength). In the presence of Br-, the products are trans- 1,2-dibromides and bromo-solvates of both cyclohexene and cyclopentene. The cyclopentenyl products have been shown to arise from the electrophilic addition of Br2/Br3 to cyclopentene, while trans-l, 2-dibromocyciohexane 67 is formed by Br- capture of the bromonium ion 66 on carbon. The Br2 required for bromination of cyclopentene results from attack by Br- on the bromonium ion 66 on Br+. On the basis of the ratio of the cyclopentyl products to 67, Br- capture of the solvolytically produced bromonium ion 66 (by attack on Br+) is 4-5 times more prevalent than attack on carbon in AcOH, and ca 25 times more preferred in MeOH123. 

---