| Autor: |
Mora, Jose R., Tosta, María, Domínguez, Rosa M., Herize, Armando, Barroso, Jenny, Córdova, Tania, Chuchani, Gabriel |
| Předmět: |
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| Zdroj: |
Journal of Physical Organic Chemistry; Dec2007, Vol. 20 Issue 12, p1021-1031, 11p, 6 Diagrams, 12 Charts, 1 Graph |
| Abstrakt: |
The gas-phase elimination kinetics of the title compounds were carried out in a static reaction system and seasoned with allyl bromide. The working temperature and pressure ranges were 200–280 °C and 22–201.5 Torr, respectively. The reactions are homogeneous, unimolecular, and follow a first-order rate law. These substrates produce isobutene and corresponding carbamic acid in the rate-determining step. The unstable carbamic acid intermediate rapidly decarboxylates through a four-membered cyclic transition state (TS) to give the corresponding organic nitrogen compound. The temperature dependence of the rate coefficients is expressed by the following Arrhenius equations: for tert-butyl carbamate logk1 (s-1) = (13.02 ± 0.46) – (161.6 ± 4.7) kJ/mol(2.303 RT)-1, for tert-butyl N-hydroxycarbamate logk1 (s-1) = (12.52 ± 0.11) – (147.8 ± 1.1) kJ/mol(2.303 RT)-1, and for 1-(tert-butoxycarbonyl)-imidazole logk1 (s-1) = (11.63 ± 0.21)–(134.9 ± 2.0) kJ/mol(2.303 RT)-1. Theoretical studies of these elimination were performed at Møller–Plesset MP2/6-31G and DFT B3LYP/6-31G(d), B3LYP/6-31G(d,p) levels of theory. The calculated bond orders, NBO charges, and synchronicity (Sy) indicate that these reactions are concerted, slightly asynchronous, and proceed through a six-membered cyclic TS type. Results for estimated kinetic and thermodynamic parameters are discussed in terms of the proposed reaction mechanism and TS structure. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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