$sup 13$C kinetic isotope effects in the pyrolysis of dimethyl ether
Intermolecular and intramolecular $sup 13$C kinetic isotope effects in the pyrolysis of dimethyl ether were measured at temperatures between 451 and 550 degreeC; initial pressures were between 14 and 1000 torr. A few experiments on the NO-inhibited reaction were carried out at 501 degreeC. Both isotope effects are of the order of 1% and decrease with increasing temperature; the temperature dependence of the intermolecular effect is the greater. No significant pressure effects were observed. The isotope effects arise in the destruction of the symmetry of the reactant in hydrogen transfer reactions of the form R+C$sup 2$$H$$sub 3$OC$sup 1$$H$$sub 3$$Yields$RH+xC$sup 2$$H$$sub 2$OC$sup 1$$H$$sub 3$, where R=CH$sub 3$, H, or NO. The method of three-element reaction coordinates was used to model the hydrogen transfer, the elements being displacements in the stretching coordinates RxxxH, HxxxC$sup 2$, and C$sup 2$XO. With adjustments of the transition state diagonal force field which are physically and chemically reasonable, the best simultaneous fit to the experimental results is obtained for reaction coordinates in which displacements in RxxxH and HxxxC$sup 2$ are large but that in C$sup 2$XO is small. The fit is not critically sensitive to the degree of transfer of H from C$sup 2$ to R in the range 25%--75%, and in that range is essentially the same for R=H, CH$sub 3$, or NO. Predictions are made of k/sub H//k/sub D/ for comparative pyrolyses of CH$sub 3$OCH$sub 3$ and CD$sub 3$OCD$sub 3$. (AIP)
- Research Organization:
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801
- NSA Number:
- NSA-33-028501
- OSTI ID:
- 4051801
- Journal Information:
- J. Chem. Phys., v. 64, no. 7, pp. 2868-2877, Journal Name: J. Chem. Phys., v. 64, no. 7, pp. 2868-2877; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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