Competitive thermal unimolecular reactions of trans-cyclopropane-d2. Collisional energy transfer

Abstract

Publication costs assisted by the National Science Foundation irans-Cyclopropane-da isomerization has been studied at low pressure as an example of a thermal, collisionally activated, competitive unimolecular reaction system. The competitive structural and geometric isomerizations have been studied in a 230-1. reactor at 480°in the pressure range near 10~3 Torr. At the lowest pressure, the ratio of the geometric to structural rate constant, kjkp, declines to kjkv ~7. The fall-off behavior is in good agreement with earlier work at higher pressures. In the presence of He bath gas, kjkp is 10% higher than for the pure substrate, when compared at identical values of kv. At low pressures the relative amounts of the competing structural and geometric processes can provide information about vibrational energy transfer on collision, although this particular system has some limitations. The kinetic expressions for this complex, reversible isomerization system are formulated. Strong collider RRKM calculations are presented.

Impact of upwardly revised Δ H f 0 of primary, secondary, and tertiary radicals on mechanistic constructs in thermal reorganizations

“…At high pressure and 4800C, the ratio of k /kp is 24 and (EO) is reported to be 0.3 kcal/mol lower than (EoI,, albeitwith the demur that a larger difference of=1 kcal/mol is more likely (23). Subsequent investigation of kg/kp at low pressures (e.g., the ratio becomes 9 at 0.02 torr) has made it possible to deduce a more reliable difference of 3.7 kcal/mol between (Eo)g and (Eo)p (24). This sensitive method depends on the obligation of all systems having E ' (Eo)p to rearrange to propene at low pressure and, thus, limit geometrical rearrangement to systems of energies (EO) ' E '-(Eo)p. Quantitative (25).…”

“…However, this prediction was not easy to reconcile with the many experiments in which single rotational processes were found to be competitive with double rotational processes (30,31). Subsequent theoretical calculations failed to confirm a large difference between single and double rotations (32) or a large barrier to ring closure (33,34 (24). These relations are shown in Fig.…”

Diradicals: Conceptual, Inferential, and Direct Methods for the Study of Chemical Reactions

“…For example, in the case of trimethylene, one must be concerned that despite decades of work, the results of several quantum theoretical calculations (13) all indicate little or no barrier to ring closure to with new values, log A (in seconds) = 14.13 and E, = 61.3 kcal/mol, derived (in an unspecified way) from results in a paper by Waage and Rabinovitch (WR) (21). However, the proposed (20) Arrhenius parameters do not correlate the experimental data, as is clear from the rate constants calculated from them, which are smaller than the reported ones (19) by factors of 11 to 15 over the available temperature range.…”

Ab initio study of C—H bond breaking in olefins. II. GVB computations on propene ↔ H + cis- or trans-propen-1-yl

“…This underlines the remarkable effect of the CH3 moiety on the processes following energy transfer to 1. Note also that trans-cyclopropane-d, isomerizes to 1-d, (33). A possible explanation, put forward by Bernardi et al (34) is that "It is conceivable that the structural isomerization proceeds by a path not involving trimethylene, and hence may not be pertinent to the [1,2] shift transition state."…”