摘要:

AbstractThe gas‐phase elimination of several polar substituents at the α carbon of ethyl acetates has been studied in a static system over the temperature range of 310–410°C and the pressure range of 39–313 torr. These reactions are homogeneous in both clean and seasoned vessels, follow a first‐order rate law, and are unimolecular. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: 2‐acetoxypropionitrile, log k1(s−1) = (12.88 ± 0.29) – (203.3 ± 2.6) kJ/mol (2.303RT)−1; for 3‐acetoxy‐2‐butanone, log ±1(s−1) = (13.40 ± 0.20) – (202.8 ± 2.4) kJ/mol (2.303RT)−1; for 1,1,1‐trichloro‐2‐acetoxypropane, log ℜ1(s−1) = (12.12 ± 0.50) – (193.7 ± 6.0) kJ/mol (2.303RT)−; for methyl 2‐acetoxypropionate, log ℜ1(s−1) = (13.45 ± 0.05) – (209.5 ± 0.5) kJ/mol (2.303RT)−1; for 1‐chloro‐2‐acetoxypropane, log ℜ1(s−1) = (12.95 ± 0.15) – (197.5 ± 1.8) kJ/mol (2.303RT)−1; for 1‐fluoro‐2‐acetoxypropane, log ℜ1(s−1) = (12.83 ± 0.15)– (197.8 ± 1.8) kJ/mol (2.303RT)−1; for 1‐dimethylamino‐2‐acetoxypropane, log ℜ1(s−1) = (12.66 ± 0.22) –(185.9 ± 2.5) kJ/mol (2.303RT)−1; for 1‐phenyl‐2‐acetoxypropane, log ℜ1(s−1) = (12.53 ± 0.20) – (180.1 ± 2.3) kJ/mol (2.303RT)−1; and for 1‐phenyl−3−acetoxybutane, log ℜ1(s−1) = (12.33 ± 0.25) – (179.8 ± 2.9) kJ/mol (2.303RT)−1. The CαO bond polarization appears to be the rate‐determining process in the transmition state of these pyrolysis reactions. Linear correlations of electron‐releasing and electron‐withdrawing groups along strong σ bonds have been projected and discussed. The p

ISSN:0538-8066    

DOI:10.1002/kin.550150302

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe liquid‐phase thermolysis of 1,2‐dihydronaphthalene was studied in a batch reactor in the range of 350–400°C. The measured product distributions were in good agreement with calculations based on a free‐radical scheme with rate constants estimated by thermochemical methods. The kinetic calculations were carried out by numerical integration and by the long‐chain approximation (LCA), which yielded a closed‐f

ISSN:0538-8066    

DOI:10.1002/kin.550150303

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractKinetic solvent isotope effects (KSIE) were measured for the hydrolyses of acetals of benzaldehydes in aqueous solutions covering the pH (pD) range of 1–6. Forp‐methoxybenzaldehyde diethyl acetal,k D +/k H += 1.8–3.1, depending on the procedure used to calculate the KSIE and on the pH (pD) range used as the basis fork H +(k D +). It is shown that this variation is an experimental artifact, and is a characteristic of KSIE measurements in general. It is recommended thatk L +be calculated from a least‐squares fit of data to the equationkobs=k L +[L+], and that the KSIE be reported ask D +/k H +. The limitation remains, however, that the KSIE measured for a variety of substances over quite different pH (pD) ranges may not be comparable to more than ℜ20%. The source of these observations is discussed in terms of small changes in the activity coefficient ratios (a specific salt effect), including the solvent isotope effect on

ISSN:0538-8066    

DOI:10.1002/kin.550150304

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe rates of electrophilic bromination of various donors follow complex kinetics which include both first‐order and second‐order dependences on bromine, especially in the less polar solvents. The second‐order rate constantksand the third‐order rate constantktare evaluated for alkene bromination in carbon tetrachloride, and they are compared to those already listed for the electrophilic brominations of substituted styrenes, arenes, and metal carbonyls in the extant literature. Despite the varying magnitudes of the second– and third‐order rate constants for these diverse donors (and in different solvents), the ratio log(ks/kt) is remarkably invariant. The mechanistic implication of this unique observation is discussed in the context of charge transfer interactions which are common to the activated complexes in the electrophilic brominations of var

ISSN:0538-8066    

DOI:10.1002/kin.550150305

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractCyano‐substituted methyl radicals (cyanomethyl–hand 2‐cyano‐2‐propyl radicals) andsyn‐andanti‐1‐cyano‐allyl radicals were generated, and their recombination kinetics in solution were investigated between −50 and +50°C by time‐resolved electron‐spin‐resonance spectroscopy. The comparison of the activation energies for recombination with the activation energies of the solution viscosities proves that the dimerizations of the radicals are diffusion controlled with rate constants on the order of 108–109M−1·s−1. In the case of cyanomethyl radicals an additional pseudo‐first‐order process, hydrogen abstraction, was detected and analyzed kinetically. Product anal

ISSN:0538-8066    

DOI:10.1002/kin.550150306

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractBy pyrolyzing di‐t‐butyl peroxide over the temperature range of 405–450 K in the presence of hexafluoroacetone the kinetics of the addition reaction (1), CH3+ (CF3)2CO→; (CF3)2C(Ȯ)CH3, have been studied. Detailed analyses have shown that the principal product of the adduct radical, (CF3)2C(Ȯ)CH3, is CF3COCH3from reaction (2), (CF3)2C(Ȯ)CH3→ CF3COCH3+ CF3. The rate constant of the addition reaction was determined to bek1(dm3/mol·s) = (1.1 ± 4.0) + 109exp(‐(3680 ± 480)/T) over the temperature range 405–450 K, based on the valuek3= 2.2 × 1010dm3/mol·s for reaction (3), 2CH3→ C2H6. The results are discussed in relation to existing data for radical addit

ISSN:0538-8066    

DOI:10.1002/kin.550150307

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractHexafluoro‐t‐butoxy radicals have been generated by reacting fluorine with hexafluoro‐2‐methyl isopropanol:Over the temperature range of 406–600 K the hexafluoro‐t‐butoxy radical decomposes exclusively by loss of a CF3radical [reaction (‐2)] rather than by loss of a CH3radical [reaction (‐1)]:The limits of detectability of the product CF3COCF3, by gas‐chromatographic analysis, place a lower limit on the ratiok−2/k‐1of ∼80. The implications of this finding in relation to the reverse radical addition reactions to the carbonyl group are briefly discussed.A thermochemical kinetic calculation reveals a discrepancy in the kinetics and thermodynamics of the decomposition and formation reactions of th

ISSN:0538-8066    

DOI:10.1002/kin.550150308

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550150301

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY