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  • 101
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 255-262 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photostimulated reaction of neopentyl halides with different nucleophiles by the SRN1 mechanism of nucleophilic substitution has been studied. Neopentyl halides do not react with carbon nucleophiles, diethylphosphite, diphenylphosphonite and azide ions, but they react with arsenide and selenide ions. The photostimulated reaction of neopentyl bromide with diphenylarsenide ions gave only the straightforward substitution product neopentyldiphenylarsine. On the other hand, the photostimulated reaction of bromobenzene with dineopentyl arsenide ions gave three arsines: dineopentylphenylarsine, neopentyldiphenylarsine and triphenylarsine. Neopentyl chloride reacts under irradiation with diphenylphosphide ions giving good yields of the substitution product.
    Additional Material: 1 Tab.
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  • 102
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 103
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 281-299 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mechanisms of the hydrolysis of urea have been investigated using the MNDO and AMI methods. All geometries were fully optimized and the transition states were characterized by calculating force constants. The results showed that: (i) The unimolecular decomposition process via the direct intramolecular proton transfer is preferred to both the A1 and the bimolecular nucleophilic attack by water, in agreement with the experimental results of Shaw et al. in the low acidity medium. (ii) The diprotonated form of urea exists as an equilibrium species, which undergoes the A2 type hydrolysis more favorably than the monoprotonated form, as Moodie et al. found in the intermediate acidity medium. (iii) The A2 hydrolysis of the monoprotonated form is very similar to those of acetamide and methyl carbamate. (iv) As the number of the solvate water molecules increases, the activation barrier for the A2 process of the monoprotonated form increases while that for the unimolecular decomposition of the free base form decreases, indicating a possibility of the barrier height reversal in the bulk solvent in favor of the latter process, thus accommodating all the experimentally found trends in the urea hydrolysis. The A1 mechanisms involving six-membered ring type intermediates can be ruled out as untenable since no such equilibrium species was obtained by both the MNDO and AM1 calculations.
    Additional Material: 17 Ill.
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  • 104
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spectroscopic evidence for the predominance of the equatorial conformers in the title compounds was confirmed by the study of derivatives containing counterpoise substituents, and by chemical equilibration of anancomeric models. ΔG27o°C [P(O)Ph2] ≳ 3·2 kcal/mol was determined in the dioxane, and ΔG55o°C [P(O)Ph2] = 1·42 ± 0·12 kcal/mol in the oxathiane. It follows then that the strong anomeric interaction observed previously in S—C—P segments does not show up in the six-membered heterocycles 2 and 7, which contain O—C—P moieties. This may be due to an inherent inability of oxygen to act as an electron donor to the axial P(O)Ph2 substituent, or to a dominant repulsive steric interaction in the axial conformers.
    Additional Material: 2 Tab.
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  • 105
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An excellent linear correlation of oxygen-17 substituent chemical shifts (SCS) for twelve α, α, α-trifluoroacetophenones with single σ+ constants, δ = 24·6σ+ + 556·3 (correlation coefficient 0·998) has been observed. However, from this plot, an SCS of 34·3 ppm for 1,1,1-trifluoroacetone will give a corresponding σ+ (γ+) value of 1·44 for a methyl group, which is not in agreement with 0·63-0·79 obtained from solvolytic rate data.
    Additional Material: 1 Ill.
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  • 106
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 383-388 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Norbornadiene, isolated in argon, xenon and nitrogen matrices at 20 K, was irradiated with UV light. Characterized by UV-VIS-IR absorption spectroscopy the photoproduct, representing a single species, was assigned to quadricyclane. This result is compared with the literature data on photochemistry of norbornadiene in the gas and liquid phase. The role of the rigid matrix environment on selectivity of the photochemical reaction is discussed.
    Additional Material: 3 Ill.
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  • 107
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 108
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 448-454 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interaction between pyridoxal-5′-phosphate (PLP) and pyridoxamine-5′-phosphate (PMP) was studied by d.c. and differential pulse polarography. Two reduction waves (or two peaks) were observed. The first wave corresponds to the reduction of the adduct and the second to the reduction of free PLP. The behaviour was similar in analogous Schiff bases. The effects of pH, PMP concentration and the capillary characteristics were studied. The apparent formation constant as a function of the pH was calculated. Thermodynamic parameters were estimated at pH 7 and 0 · 1 M ionic strength. The polarographic and kinetic results show that the overall electrode process appears to be irreversible in a basic medium.
    Additional Material: 4 Ill.
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  • 109
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 476-483 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dipole moments of para-substituted benzoyl chlorides and bromides, partly measured in benzene and partly recalculated from elderly literature, were analysed in terms of bond moments and additional contributions expressing the conjugation. Although the gross moments are similar, their decomposition yields different pictures for acyl chlorides and bromides. Only in the latter can significant electron transfer from the halogen be observed. On the other hand, conjugation with the benzene nucleus is strong in both aromatic acyl chlorides and bromides, but stronger in chlorides. There is agreement with the evidence from some other physical quantities but not from all.
    Additional Material: 2 Ill.
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  • 110
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Benzyl cations, free of counter ions, have been generated from the nuclear decay of tritium atoms contained exclusively in the side-chain of multi-labelled toluene and allowed to react in competition experiments with benzene and toluene. The aromatic substitution was studied in both the gaseous and liquid phase, employing pure aromatics or aromatics dissolved in n-hexane, carbon tetrachloride and nitromethane as the reaction medium. In the gaseous systems, at 20 Torr total pressure, High meta substitution of toluene indicates extensive isomerization of the excited intermediates, while the increase of the kT/kB value in the Presence of NH3 suggests that selective transalkylation competes with proton transfer to ammonia from the benzyl cation adducts with benzene, but not with toluene. High positional and low substrate selectivities were measured in solution, the decrease in kT/kB (from 2·8 to 1·7) in the different solvents being accompanied by an increase in the o/2p ratio. Competition experiments between benzene and methanol indicate that the reaction is not diffusion controlled. The influence of the reaction medium on the substrate selectivity is explained by postulating the formation of a cation-solvent adduct, where the solvent molecule undergoes displacement by the substrate. Positional selectivity would be controlled in a subsequent step.
    Additional Material: 1 Tab.
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  • 111
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The basic hydrolysis of 2,4-dinitrochlorobenzene (DNCB) and 2,4-dinitrofluorobenzene (DNFB) was studied in the presence of β-cyclodextrin (CDOH) and in the presence of hydroxy-functionalized micelles containing either a primary hydroxy group [hexadecyl-2-hydroxyethyldimethylammonium bromide (CHEDAB)] or a secondary hydroxy group [headecyl-2-hydroxypropyldimethylammonium bromide (CHPDAB) and 2-hydroxyhexadecyltrimethylammonium bromide (2-OHCTAB)].In all systems a biphasic reaction was observed. The first phase consisted of a competition between the additive (either micelle or cyclodextrin) and hydroxide ion for the aromatic substrate, and the second phase consisted of the hydrolysis of the trapped aryl micellar or cyclodextryl ether.The percentage of trapping of the aromatic substrate by the cyclodextrin was similar to that found for reactions in the hydroxy-functionalized micelles (CHPDAB and 2-OHCTAB) which contained secondary hydroxy groups. The relative rates of reaction for DNFB and for DNCB, i.e. F/Cl rate ratios, in the presence of CDOH were similar to those obtained in the presence of 2-OHCTAB but less than that obtained in the presence of CHEDAB. These results support the assumption that in CDOH the secondary hydroxy groups of C-2 or C-3 are involved in covalent bond formation with the aromatic substrate rather than the primary hydroxy group of C-6. All the reactions studied proceed much more slowly in the presence of CDOH than in the presence of the hydroxy-functionalized micelles. This may reflect a catalytic effect of the positively charged surface present in the micelles but not in the cyclodextrin.
    Additional Material: 3 Ill.
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  • 112
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Using the solvatochromic indicator method, a scale of solvent hydrogen-bond basicity, β1 (General), has been set up using a series of double regression equations, \documentclass{article}\pagestyle{empty}\begin{document}$$ \nu = \nu _0 + s\pi _1^* + b\beta _1 $$\end{document} for 11 aniline-type indicators. A similar solvent scale, β1 (Special), has been constructed by the homomorphic comparison method using only results by Laurence et al. on the indicators 4-nitroaniline and 4-nitro-N,N-dimethylaniline. Results are available from our previous work on a general solute scale, β2H, and we have also obtained a special solute scale, β2 (pKHB) from available log K values for hydrogen-bond complexation of bases with 4-fluorophenol in CCl4. However, the two solute β2 scales are virtually identical.It is shown that there is a general connection between β1(General) and β2H, with r = 0·9775 and s.d. = 0·05 for 32 compounds, and between β1(Special) and β2H, with r = 0·9776 and s.d. = 0·06 for the same 32 compounds. The latter correlation over 60 compounds yields r = 0·9684 and s.d. = 0·07. However, there are so many compounds in these regressions for which the differences in the solvent and solute β values are larger than the total expected error of 0·07 units that the use of β1 to predict β2 or vice versa is a very hazardous procedure. About 70 new β1 values obtained by the double regression method are also reported.
    Additional Material: 6 Tab.
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  • 113
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 573-579 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The MM2 force field has been extended so that calculations may be carried out on siloxanes. The parameters chosen give a good fit to available experimental data.
    Additional Material: 2 Tab.
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  • 114
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 602-610 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In order to assist in the interpretation of the D5h molecular structure of [45] (1,2,3,4,5)ferrocenophane (1) obtained from x-ray crystallographic analysis, a hypothetical hydrocarbon C30H40 (2) was derived from 1 by removing the iron atom and subjected to geometry optimization by molecular mechanics. A stable D5 conformer was found for 2, which has a g+ g- g+ helical bridge conformation and a ring-ring distance almost identical with that in 1 and ferrocene itself. Optimization of a perhydrogenated hydrocarbon model gave a highly strained C1 structure.
    Additional Material: 2 Ill.
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  • 115
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 623-630 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photolysis of dichlorodiphenylmethane in glassy 2-methyltetrahydrofuran at 77 K results in the formation of diphenylcarbene and the diphenylchloromethyl radical, which were detected by their fluorescence emission and excitation spectra. The relative yields of the carbene and biradical are shown to vary dramatically as a function of photolysis time. The photolability of the diphenylchloromethyl radical is also demonstrated. These results were interpreted in terms of a two-step mechanism, in which the diphenylchloromethyl radical is an intermediate in the formation of diphenylcarbene.
    Additional Material: 2 Ill.
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  • 116
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The formation of a σ-like complex by reaction between 1,3,5-trinitrobenzene and 1,8-diazabicyclo [5.4.0]-undec-7-ene was investigated in toluene at various temperatures. The kinetic data showed autocatalytic behaviour. Inspection of the reaction mixtures at zero reaction time indicated the presence of an equilibrium preceding the attack of the nucleophile, affording a molecular complex (substrate-nucleophile) which is responsible for the observed kinetic features. The present and the previous data led to the conclusion that the catalytic behaviours usually observed in SNAr reactions (in apolar solvents with amines as nucleophiles) are better explained by the presence of substrate-catalyst interactions than by catalysis on departure of the proton and leaving group from the zwitterionic intermediate.
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  • 117
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 118
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ups and downs, and reasons therein, of the π-complex theory of the mechanism of the benzidine rearrangements, and the possible role of π-complexes in a newer understanding of the rearrangements, are described.
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  • 119
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 531-539 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acid-catalysed condensation of resorcinol with aromatic aldehydes results in 2,8,14,20-tetrasubstitued calix[4] areneoctols. Sixteen compounds of this type containing different aromatic substituents were synthesized. The ring closure step, under the conditions of the reaction, is a reversible process. Four configurations are possible for every constitution, viz. cccc, cctt, ccct and ctct, but only cccc and cctt were formed in detectable amounts. In seven cases the thermodynamically more stable cccc isomers (1a-5a, 7a, 8a) and also the kinetically controlled cctt isomers (1b-5b, 7b, 8b) could be isolated. The configurations of the compounds were assigned by temperature-dependent 1H NMR analysis. The conformational motions of the macrocyclic ring permit only the cccc isomers to show coalescence for the signals of the aromatic Hb protons. The coalescence temperature was determined for isomers 1a (ΔG384≠ = 83·5 kJmol-1) and 3a (ΔG369≠ = 83·7 kJ mol-1). For steric reasons the ‘chair-chair’ conformers B and the ‘quasi-boat-chair’ conformers F are favoured. 1H and 13C NMR shifts show that compounds 1a-5a and 1b-5b have a quasi-axial arrangement of the aromatic substituents, whereas 6-9 have a quasi-equatorial arrangement of the substituents.
    Additional Material: 5 Ill.
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  • 120
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: IR spectroscopy is presented as a convenient means to monitor the formation of acyl (and alkyl) cations from corresponding acid chlorides, with Lewis acids at low temperature in the solid state. Phenylacetyl chloride is co-deposited (under vacuum at -173°C with antimony pentafluoride on a KBr window), as in the ‘molecular beam’ method of cation generation. The initial IR spectrum of the deposition shows (in addition to starting materials) that a small amount of phenylacetyl cation (2274 cm-1) has been formed. Warming the solid matrix to -123°C Promotes the smooth conversion of acid chloride to acyl cation. Ultraviolet irradiation (through quartz windows) at -123°C to -73°C facilitates this conversion but does not result in the loss of carbon monoxide from the acyl cation to form benzyl cation. When benzyl chloride is used in place of phenylacetyl chloride, there is no noticeable difference between IR spectra taken before and after warming and/or photolysis of the solid deposition.
    Additional Material: 1 Ill.
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  • 121
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 214-224 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solvolysis of 21 different 3- or 17-androstanyl tosylates or chlorides with halogen, hydroxy or oxo substituents in 17- or 3-position shows rate constant variations in hexafluoro isopropanol of up to 6·3 with regular differences for epimeric substituents. Similar variations ae seen over a distance of ∼10 Å in 13C-NMR shifts at C-17-ones of androstan-17-ones with varied halogen substituents in C-3, whereas the shielding observed at other distant carbon atoms excludes significant through bond effects. It is shown how, on the basis of suitable Coulomb-type equations and of force field minimized geometries, both the stability variation of carbocationic transition states and the carbonyl group polarization are predictable by linear electric field effects, using the same parametrization.
    Additional Material: 1 Ill.
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  • 122
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 263-270 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reactivity of dialkyl 2-(dimethylamino)ethyl phosphates, (RO)2P(O)OCH2CH2NMe2 (R = Me, PhCH2) was studied in aqueous solutions. Depending on the initial substrate's concentration, reaction can involve the unimolecular fragmentation to N,N-dimethylaziridinium dialkylphosphate, or the bimolecular isomerization to the zwitterionic derivative. The latter reaction proceeds via two consecutive SN2 steps and involves the formation of two ionic intermediates which were synthesized independently and allowed to react to give the zwitterionic product. Rate constants for the isomerization of the dimethyl ester (R = Me), as well as rate constant for the reaction between the corresponding intermediates have been determined, and the reactivity of the dimethyl ester has been compared with that of the dibenzyl derivative.
    Additional Material: 1 Ill.
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  • 123
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal and molecular structures of dimesitylketene (1) and bis(3,5-dibromo-2,4,6-trimethylphenyl)ketene (2), the first free ketenes to be studied by X-ray diffraction, have been determined. The molecules of 1 and 2 have crystallographic C1 and C2 symmetry, respectively, and exist in a propeller conformation. Molecular mechanics calculations of 1 and 2 using a modification of Allinger's new allene parameters reproduce satisfactorily the structural parameters of the ketenes. The torsional angles of the aryl rings in 1 and 2 are similar (ca. 50°) and are regarded as ‘intrinsic’ values for a 1,1-dimesitylvinyl propeller. From the similarity in aryl torsional angles in 1 and 2 it is concluded that the buttressing effects in 2 (if any) are not markedly manifested in the structural parameters of 2.
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  • 124
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 323-330 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photoreactions of Cr(CO)5(Im) (Im = 1,3-dimethyl-4-imidazolin-2-ylidene) have been investigated by laser flash and continuous photolysis. Quantum yields for the disappearance of Cr(CO)5(Im) in benzene under Ar or CO were very low, although transients observed by laser flash photolysis reacted rapidly with CO. This suggests that photodissociation of the carbene ligand is very minor. The laser flash photolysis at 337 nm in benzene (B) gave a transient (λmax = 630 nm), which converted to the second transient (λmax = 455 nm) within ∼100 ns. The kinetic studies of these transients revealed that the first one is a ‘free’ coordinatively unsaturated species (Cr(CO)4(Im)) and the second one carries a solvent molecule as a ligand (Cr(CO)4(Im)(B)). From the comparison of Cr(CO)4(Im) and Cr(CO)5, apparently lower reactivity of Cr(CO)5 was found to be due to the strong coordination of a solvent molecule. The Im ligand neutralizes the deficit of electron density on Cr. A simple synthesis of Cr(CO)5(Im) was also described.
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  • 125
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 359-362 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction pathway of urea formation by selenium-catalysed carbonylation of secondary amines with carbon monoxide in the presence of oxygen was studied using piperidine as a secondary amine. It was established that selenium reacts with carbon monoxide and piperidine to give carbamoselenoate as an intermediate, which affords biscarbamoyl diselenide by the oxidation with molecular oxygen. Aminolysis of biscarbamoyl diselenide gives the urea derivative, accompanying the regeneration of selenium catalyst.
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  • 126
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 377-382 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rates of N-methylation of pyridine and its ring-substituted derivatives by trimethyl phosphate were measured in D2O and in CDCl3. Relative rates, together with the solvent activity coefficients of substrates for the transfer form chloroform to water, were used for determining the solvent activity coefficients of the activated complexes for this SN2 reaction. The results indicate early activated complexes for all pyridines, with the most nucleophilic substrate showing the most reactant-like activated complex.
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  • 127
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    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 389-409 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A gas-phase experimental investigation of the competition between carbon and oxygen alkylation of a series of cyclic and acyclic enolate ions is described. Perfluoropropylene is shown to react in a characteristic way with oxyanions and carbanions to produce distinctive ionic products. The relative yields of these products formed in reactions with ambident enolate ions provides a measure of their intrinsic carbon vs. oxygen regioselectivity. The results for a series of enolates derived from aldehydes, ketones, esters, amides and related compounds show a wide range of reactivity which is a function of the nature of the central substituent. Most aldehyde and ketone enolates react mainly through oxygen, while enolates with σ-acceptor of π-donor type central substituents react mainly thorugh carbon. Ring-size in cyclic ketone enolates also influences C vs. O regioselectivity, i.e. small-ring enolates react mainly through carbon, while larger ring enolates (C7-C9) react preferentially through oxygen. The enolate reactivity patterns can be generally accounted for by the keto-enol energy differences for the parent carbonyl compounds, although some exceptions are evident. The origins of the highly variable, kinetically determined regioselectivities are discussed.
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  • 128
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    Journal of Physical Organic Chemistry 2 (1989), S. 417-424 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two organometallic reagents, butyllithium in heptane solution and dibutylmercury in the gas phase, have been studied by means of core electron spectroscopy. The property of particular interest was the charge polarization as reflected by the ESCA shifts. In the butyllithium compound the C1s binding energy is shifted to a lower value by 1·8 eV for C-1 (situated closest to the Li+ ion) relative to the heptane solvent carbon. This is due to the anionic character of the C-1. The interpretation of the experiments was supported by comparing the results with ab initio calculations made on geometry-optimized butyllithium, butyl anion and butane.
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  • 129
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    Journal of Physical Organic Chemistry 2 (1989), S. 455-466 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Mixtures of bicyclo[3.2.0]hept-2-ene and bicyclo[2.2.1]hept-2-ene, with one isomer labeled with two deuterium atoms, were isomerized in the gas phase at 276 °C. By following the concentration ratios of d0 and d2 versions of bicyclo[2.2.1]hept-2-ene as functions of time one finds that the partitioning of bicyclo[3.2.0]hept-2-ene between the primary products bicyclo[2.2.1]hept-2-ene and cyclopentadiene plus ethene is 2:1. This and earlier stereochemical results permit the calculation of the partitioning of the [3.2.0] olefin between the orbital symmetry allowed [1,3] carbon shift-with-inversion product and several forbidden or non-concerted reaction channels (approximately 1:1) and the stereochemistry of the ethene d2 formed from exo,exo-[6,7-2H2]bicyclo[3.2.0]hept-2-ene directly (1:1 E: Z).
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  • 130
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    Journal of Physical Organic Chemistry 2 (1989), S. 187-204 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reaction products of bifunctional chain molecules with structure X—(CH2)n—Y may critically depend on the chain length n. When the chain length is short (n ≤ 5), reaction products particular to an intramolecular reaction can be dominant, while a process corresponding to an intermolecular reaction between X—CH3 and H3C—Y may take place for higher homologues having large n (≥10). The reaction switching dependent on n is explained in terms of the encounter probability for both end groups (X and Y) with conformations pertinent to product formation. The reaction switching of this sort is discussed on the basis of a reactivity profile recorded as a function of the chain length. Similar reactivity profiles have been observed for thermal Friedel-Crafts cyclization and photo-Smiles rearrangement/photoredox reaction. It is anticipated that the magic methylene chain length of 7 may give rise to an appreciable decrease in reaction yields (e.g. ‘difficulty in medium-sized ring closure’) or an anomalous switching of reaction pathways due to chain length effects.
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  • 131
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: ΔG, ΔH and TΔS of transfer of 25 aliphatic and aromatic solutes from 2,2,4-trimethylpentane to aqueous buffer (pH 7) at 298 K have been examined in terms of intrinsic volumes and the solvatochromic parameters π*, δ, β and α of the pure solutes Correlations of the form \documentclass{article}\pagestyle{empty}\begin{document}$$ XYZ = XYZ_0 + {{mV_{\rm I} } \mathord{\left/ {\vphantom {{mV_{\rm I} } {100}}} \right. \kern-\nulldelimiterspace} {100}} + s\pi ^* + d\delta + d\beta + a\alpha $$\end{document} indicate that the thermodynamic quantities of transfer are unequally affected by solute properties; most notably, for aromatic solutes the cavity term mVI/100 is a principal (unfavorable) factor affecting TΔS, but has little effect on ΔH. Transfer to water is favored by increasing solute π* (dipolarity-polarizability), β (H-bond basicity) and α (H-bond acidity), because water has greater dipolarity, H-bond acidity and H-bond basicity than trimethylpentane. Hydrogen bonding contributes exothermically to ΔH, but unfavorably to TΔS, as would be expected from a loss of transitional entropy. Correlations of ΔG, ΔH and TΔS with solute VI/100, β, α, μ2 and polarizability function [(n2 - 1)/(n2 + 2)] give closely comparable results.
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  • 132
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    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 133
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    Journal of Physical Organic Chemistry 2 (1989), S. 585-601 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Triarylaminium salts smoothly catalyze the cyclopropanation of dienes, styrenes and tetrasubstituted alkenes by ethyl diazoacetate. The reactions are regioselective and, in the case of additions to conjugated dienes, cyclopropane-periselective. A cation radical chain mechanism involving carbene transfer from ethyl diazoacetate to a substrate cation radical is proposed.
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  • 134
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    Journal of Physical Organic Chemistry 2 (1989), S. 646-652 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Using a series of equations connecting experimental and theoretical values, it is possible to discuss the origin of the N-methylation effect in azoles dissolved in water and dimethyl sulphoxide. The existence in the azoles studied of a linear relationship between the gas → solution transfer enthalpies and the charge on the pyrrole hydrogen atom demonstrated the fundamental importance of the loss of an active centre for solvation. For the imidazole-N-methylimidazole pair, the complete thermochemical cycle has been determined, allowing the apparent lack of an effect of N-methylation on the basicity in solution to be discussed.
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  • 135
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    Journal of Physical Organic Chemistry 2 (1989), S. 660-671 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the oxidation of seven substituted ethanols by sodium N-bromobenzenesulphonamide or bromamine-B (BAB) in the presence of HCl was studied at 45 °C. The rate shows a first-order dependence on [BAB]0 and is fractional in [alcohol]0, [H+] and [Cl-]. Ionic strength variations, addition of benzenesulphonamide reaction product and variation of dielectric constant of the medium have no effect on the rate. The solvent isotope effect kH2O′/kD2O′ ≈ 0·97. The rates do not correlate satisfactorily with Taft's substituent constants. Activation parameters ΔH≠, ΔS≠, ΔG≠ and log A were calculated by studying the reaction at different temperatures (308-323 K). It was found that ΔH≠ and ΔS≠ are linearly related and an isokinetic relationship is observed with isokinetic temperature β = 393 K, indicating enthalpy as a controlling factor.
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  • 136
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    Journal of Physical Organic Chemistry 2 (1989) 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 137
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    International Journal of Chemical Kinetics 21 (1989), S. 1069-1076 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relative rate technique has been used to determine rate constants for the reaction of bromine atoms with a variety of organic compounds. Decay rates of the organic species were measured relative to i-butane or acetaldehyde or both. Using rate constants of 1.74 × 10-15 and 3.5 × 10-12 cm3 molecule-1 s-1 for the reaction of Br with i-butane and acetaldehyde respectively, the following rate constants were derived, in units of cm3 molecule-1 s-1: 2, 3-dimethylbutane, (6.40 ± 0.77) × 10-15; cyclopentane, (1.16 ± 0.18) × 10-15, ethene, (≤2.3 × 10-13); propene, (3.85 ± 0.41) × 10-12; trans-2-butene, (9.50 ± 0.76) × 10-12, acetylene, (5.15 ± 0.19) × 10-15; and propionaldehyde, (9.73 ± 0.91) × 10-12. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The results are discussed with respect to the mechanisms of these reactions and their utility in serving as a laboratory source of alkyl and alkyl peroxy radicals.
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  • 138
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    International Journal of Chemical Kinetics 21 (1989), S. 1153-1160 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Uncertainty sometimes exists in determining initial reaction rates from experimental data. A method, originally proposed by Wilkinson [9] for estimating orders and rate constants for simple batch nth order reactions, has been generalized to complex kinetic systems. This method yields very accurate initial rates for all systems and extends the conversion range of experimental investigation of initial rates well beyond the “zero-order” region. Accurate initial rates are required in analytical methods used for screening alternate reaction mechanisms.
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  • 139
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    International Journal of Chemical Kinetics 21 (1989) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 140
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    International Journal of Chemical Kinetics 21 (1989), S. 499-517 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants of Br atom reactions have been determined using a relative kinetic method in a 20 l reaction chamber at total pressures between 25 and 760 torr in N2 + O2 diluent over the temperature range 293-355 K. The measured rate constants for the reactions with alkynes and alkenes showed dependence upon temperature, total pressure, and the concentration of O2 present in the reaction system.Values of (6.8 ± 1.4) × 10-15, (3.6 ± 0.7) × 10-14, (1.5 ± 0.3) × 10-12, (1.6 ± 0.3) × 10-13, (2.7 ± 0.5) × 10-12, (3.4 ± 0.7) × 10-12, and (7.5 ± 1.5) × 10-12 (units: cm3 s-1) have been obtained as rate constants for the reactions of Br with 2,2,4-trimethylpentane, acetylene, propyne, ethene, propene, 1-butene, and trans-2-butene, respectively, in 760 torr of synthetic air at 298 K with respect to acetaldehyde as reference, k = 3.6 × 10-12 cm3 s-1.Formyl bromide and glyoxal were observed as primary products in the reaction of Br with acetylene in air which further react to form CO, HBr, HOBr, and H2O2. Bromoacetaldehyde was observed as an primary product in the reaction of Br with ethene. Other observed products included CO, CO2, HBr, HOBr, BrCHO, bromoethanol, and probably bromoacetic acid.
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  • 141
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    International Journal of Chemical Kinetics 21 (1989), S. 801-827 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aromatic ring-retaining products formed from the gas-phase reactions of the OH radical with benzene and toluene, in the presence of NOx, have been identified and their formation yields determined. These products, and their formation yields, are as follows: from benzene - phenol, 0.236 ± 0.044; nitrobenzene, {(0.0336 ± 0.0078) + (3.07 ± 0.92) × 10-16[NO2]}; from toluene - benzaldehyde, 0.0645 ± 0.0080; benzyl nitrate, 0.0084 ± 0.0017; o-cresol, 0.204 ± 0.027; m- + p-cresol, 0.048 ± 0.009; m-nitrotoluene, {(0.0135 ± 0.0029) + (1.90 ± 0.25) × 10-16[NO2]}, where the NO2 concentration is in molecule cm-3 units. The formation yields of o- and p-nitrotoluene from toluene were ca. 0.07 and 0.35 that of m-nitrotoluene, respectively. The observations that the nitro-aromatic yields do not extrapolate to zero as the NO2 concentration approaches zero are not consistent with current chemical mechanisms for these OH radical-initiated reactions, and suggest that under the experimental conditions employed in this study the hydroxycyclohexadienyl radicals formed from OH radical addition to the aromatic ring react with NO2 rather than with O2. However, these data concerning the nitroaromatic yields are consistent with our previous conclusions that many of the nitrated polycyclic aromatic hydrocarbons present in ambient air are formed, at least in part, in the atmosphere from OH radical reactions.
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  • 142
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    Keywords: Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: A modified laser photolysis/laser-induced fluorescence technique has been used to measure atmospheric pressure absolute rate coefficients for the reaction of hydroxyl (OH) radicals with the chlorinated methanes (CH3Cl, CH2Cl2, and CHCl3). Data have been obtained for these compounds over the widest temperature range (292-800 K) that has been reported in the literature using a single experimental apparatus. The temperature dependence of the rate data is best represented by the following three-parameter expressions: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 3} {\rm Cl:}\,{\rm 8}{\rm .38}\,\, \pm \,\,1.07\,\, \times \,\,10^{ - 16} \,{\rm T}^{{\rm 1}{\rm .38} \pm {\rm 2}{\rm .01/0}{\rm .71}} \exp [- 2387.4\,\, \pm \,\,142.8/RT]({\rm cm}^3 /{\rm molec - s)}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 2} {\rm Cl}_{\rm 2} {\rm :}\,\,1.{\rm 52}\,\, \pm \,\,0.16\,\, \times \,\,10^{ - 16} \,{\rm T}^{{\rm 1}{\rm .58} \pm 0.45} \exp [- 1236.3\,\, \pm \,\,119.5/RT]({\rm cm}^3 /{\rm molec - s)}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CHCl}_{\rm 3} {\rm :}\,\,1.{\rm 92}\,\, \pm \,\,0.21\,\, \times \,\,10^{ - 20} \,{\rm T}^{{\rm 2}{\rm .78} \pm 0.34/0.42} \exp [- 188.3\,\, \pm \,\,119.3/RT]({\rm cm}^3 /{\rm molec-s)}$$\end{document} Uncertainties in the pre-exponential and exponential term are expressed as 95% confidence intervals. For the temperature exponent, error limits represent a ±10% change in the total error of best fit.The degree of curvature in the Arrhenius plots appeared to increase with increasing Cl substitution of the reactant. However, the uncertainty in the temperature exponent for the CH3Cl data was large in comparison with the other chlorinated methanes. Thus, data of greater precision at elevated temperatures are necessary to further explore this relationship. The rate coefficients were compared with recent semiempirical and transition state theory models for haloalkane-OH hydrogen transfer reactions over a temperature range of 250-800 K. The transition state model of Cohen and Benson was in excellent agreement with the CH3Cl and CH2Cl2 data. The semiempirical structure activity relationship developed by Atkinson represented the best fit of the CHCl3 data, although it underestimated the experimental data by more than a factor of 2 at 800 K. The extreme care used to remove and alayze for reactive impurities along with the agreement with other experimental studies suggests that transition state and semi-empirical models for CHCl3 must be modified to account its reaction behavior at high temperature.
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  • 143
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    International Journal of Chemical Kinetics 21 (1989) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 144
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    International Journal of Chemical Kinetics 21 (1989), S. 1003-1014 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the gas-phase thermal decomposition of 1,1,2,2-tetrafluorocyclopropane (TFC) to 1,1-difluoroethylene and CF2 was studied in the temperature range of 507.0-577.0 K and with a total pressure of 200 to 300 torr of a 1:100 mixture of reactant and C2H4. Also at 557.0 K experiments were made at different total pressures, in the range 2-20 torr with neat TFC and between 20-300 torr with the C2H4/TFC mixture, confirming that the reaction is in the high pressure limit. The reaction is first-order and the rate constants fit the following Arrhenius relationship: \documentclass{article}\pagestyle{empty}\begin{document}$$\log \,k/(s^{ - 1}) = (14.02 \pm 0.16) - (45,150 \pm 200)/4.576T$$\end{document} From this value of the activation energy, the data for the decomposition of chemically activated TFC were revised. The new results yield a minimum energy of the activated molecule of 98 ± 4 kcal/mol and ΔHf°(TFC) = -155.4 ± 7 kcal/mol, while an analysis of the kinetic data yields ΔHf°(TFC) = -159 ± 9 kcal/mol.
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  • 145
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    International Journal of Chemical Kinetics 21 (1989), S. 445-464 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An earlier correlation between isolated CH stretching frequencies, visCH, and experimental CH bond dissociation energies, in hydrocarbons, fluorocarbons, and CHO compounds, is updated. A stabilization energy, EvS, which reflects only the properties of the radical, is defined by the deviation of a point from the above correlation. EvS values for a variety of radicals are listed and discussed. In H—C—N and H—C—O compounds EvS is low or negligible, due to the low visCH found in these compounds. The conventional definition of ES then represents a serious misnomer, which distracts attention from the probable source of discrepancies between experimental and ab initio values of DH°(C—H), namely, the parent molecules. Stereo electronic effects concerned with the breaking of CH bonds are predicted in a variety of situations.Some experimental determinations of DH°(C—H), viz., in C2H4, HCOOH, CH3CHO, CH3NH2, are considered to be probably in error.Schemes for partitioning energies of atomization into ‘standard’ or ‘intrinsic’ bond energies are criticized.
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  • 146
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    International Journal of Chemical Kinetics 21 (1989), S. 547-560 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenol pyrolysis has been studied in a turbulent flow reactor by analyzing concentration-time profiles of three major decomposition products: carbon monoxide, cyclopentadiene, and benzene. Experimental conditions were P = 1 atm, T = 1064 - 1162 K, and initial phenol concentrations of 500-2016 ppm. The major experimental observations were that the decomposition product profiles were nearly linear as a function of time and that the overall rate of carbon monoxide production was greater than that of cyclopentadiene. The rate difference is explained by a mechanism which includes a radical combination reaction of cyclopentadienyl and phenoxy. With literature and approximate rate coefficient data, the mechanism reproduced the experimental observations very well. The mechanism and data provide estimates of rate coefficients for the phenol decomposition initiation step, abstraction of hydrogen from phenol by cyclopentadienyl, and the phenoxy-cyclopentadienyl combination, all of which have not been available in the literature.
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  • 147
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    International Journal of Chemical Kinetics 21 (1989) 
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 148
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    International Journal of Chemical Kinetics 21 (1989), S. 635-642 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Relaxation rate constants for the collisional deactivation of I (2P1/2) by halogen cyanides were measured by time resolved atomic absorption. The values obtained were (1.2 ± 0.1) × 10-15, (5.2 ± 0.7) × 10-15, and (2.6 ± 0.4) × 10-14 cm3 molecule-1 s-1 for ClCN, BrCN, and ICN, respectively. Quenching efficiencies are discussed in view of the stability of linear molecules to form the transient complex as well as the similarities assumed between halogen cyanides and interhalogen diatomic molecules.
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  • 149
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    International Journal of Chemical Kinetics 21 (1989), S. 677-687 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants have been determined for the reactions of SO4- with a series of alcohols, including hydrated formaldehyde. The SO4- radical was produced by the laser-flash photolysis of persulfate, S2O82-. Rate constants for the reactions of SO4- with alcohols range from 1.0 × 107 for methanol to 3.4 × 108 M-1 s-1 for 1-octanol. Rate constants for the reactions of SO4- with deuterated methanol and ethanol are lower by about a factor of 2.5. For methanol, ethanol, and 2-propanol, the temperature dependence of the rate constant was determined over the range 10-45°C.
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  • 150
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    International Journal of Chemical Kinetics 21 (1989) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 151
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    International Journal of Chemical Kinetics 21 (1989), S. 757-763 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The catalytic activity of iodine monobromide and iodine monochloride were investigated in the reaction, Et3SiOBun + BusOH ⇌ Et3SiOBus + BunOH. Pseudo first-order rate constants were measured by gas chromatography, at 10°, 20°, 30°, and 40°C for iodine monobromide and at 10°, 20°, and 30°C for iodine monochloride, on reaction mixtures containing both butanols in excess. The catalytic coefficients of both catalysts were evaluated from the observed rate constants as follows: \documentclass{article}\pagestyle{empty}\begin{document}$$k_{2{\rm IBr}} = 9.5 \pm 10^8 \exp \,(- 54.8 \times 10^3 /RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{ - 2{\rm IBr}} = 12.3 \pm 10^8 \exp \,(- 53.3 \times 10^3 /RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{2{\rm ICI}} = 10.7 \pm 10^8 \exp \,(- 54.6 \times 10^3 /RT)$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{ - 2{\rm ICI}} = 13.2 \pm 10^8 \exp \,(- 53.1 \times 10^3 /RT)$$\end{document}The activation paramaters were estimated from these data, and were compared with the values for iodine catalysis. These results are consistent with the mechanism previously proposed.
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  • 152
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    Keywords: Chemistry ; Physical Chemistry
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  • 153
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    International Journal of Chemical Kinetics 21 (1989), S. 909-922 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermochemical kinetics formulation of conventional transition state theory for bimolecular reactions allows for a separate contribution from each degree of freedom (translation, rotation, vibration, etc.) in the activated complex to the entropy and heat capacity of activation, and thus to the preexponential terms in the Arrhenius rate expression, k = ATn exp(-B/T). The number of vibrations and (possibly hindred) internal rotations varies depending on the nature of the reaction: atom + diatom, diatom + linear polyatom, etc. The temperature exponent n can be evaluated explicitly for each type of reaction if the harmonic oscillator-rigid free rotor approximation is valid for the reagents and activated complex and if the contribution from tunneling is small. Various reaction types are examined successively, and n is evaluated for each case. The possible contributions of other factors (vibrational anharmonicity, hindered internal rotation, tunneling, “looseness” of activated complex) to the value of n are also considered.
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  • 154
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    International Journal of Chemical Kinetics 21 (1989), S. 967-976 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selectivity-reactivity correlations are shown to support a biradical pathway for the gas phase thermal Diels-Alder reactions of cyclohexa-1,3-diene with substituted ethenes except for those involving a carbonyl group.
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  • 155
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    International Journal of Chemical Kinetics 21 (1989), S. 51-61 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have carried out a kinetic study of the 4-pyridinecarboxaldehyde plus n-hexylamine system, at 25°C, in water-dioxan mixtures (0-60% v/v) and in the pH range pKa + 1.5 〉 pH 〉 pKa - 1.5, where pKa is the pK value of the conjugate acid of the amine. The results obtained could be interpreted in terms of a rate constant for Schiff's base hydrolysis and a rate constant for the reaction between the nonprotonated n-hexylamine and the nonhydrated form of 4-pyridinecarboxaldehyde. Both constants decrease sharply as the dioxan content of the solvent increases, in a manner consistent with Marshall's model [J. Phys. Chem., 74, 346 (1970)]. It is suggested that the transition state of the rate-limiting step (carbinolamine dehydration) is highly solvated by water molecules and has a high separation of charges.
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  • 156
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    International Journal of Chemical Kinetics 21 (1989), S. 31-50 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetics of oxidation of thiosemicarbazide (TSC) and its hydrazone (Benzaldehyde thiosemicarbazone) by chloramine-T (CAT) and dichloramine-T (DCT) in aqueous methanol medium in the presence of perchloric acid has been studied. Oxidation of TSC by both the oxidants showed first order dependences in [oxidant], fractional order in [TSC] and nearly inverse first order in [H+]. The conversion of TSC into its benzaldehyde hydrazone changed the rate dependence in [CAT] from first to second order, while the dependence in [DCT] remained unchanged. The dependence in [TSC] changes from fractional order to zero order in both CAT and DCT oxidations. The rate followed inverse fractional order kinetics in [H+] in both the cases. Increase in ionic strength of the medium slightly decreased the rate, while the decrease in dielectric constant of the medium increased the rates of oxidations for both the oxidants. But the addition of reaction products, p-toluenesulphonamide and chloride had no effect on the rate. Oxidation of TSC with both the oxidants has been shown to follow Michaelis-Menten type mechanism. In hydrazone oxidations oxidants have been shown to disproportionate in slow steps to HOCl, which in turn attacks the substrate in fast steps to give the final products. [TSC] was varied at different temperatures and the constants of rate limiting steps were calculated at each temperature. Using the latter constants the activation parameters have been computed from the Arrhenius plots. The rate constants have been predicted from the rate law for the variation of [H+] at constant [TSC] and [oxidant]. The predicted values are in reasonable agreement with the experimental rate constants, providing additional support to the suggested mechanisms.
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  • 157
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    International Journal of Chemical Kinetics 21 (1989), S. 83-99 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the elementary sensitivity densities, a reaction rate sensitivity gradient is obtained which is the derivative of the rate of species concentration change with respect to the rate coefficient. The dimensionless (log-normalized) form of the reaction rate sensitivity gradient is the ratio of the rate of concentration change of species i due to elementary reaction j and the net rate of concentration change of species i. This result provides a mathematical basis for the use of various forms of reaction rate analyses in the study of complex reaction mechanisms. The kinetic information inherent in the relative reaction rate matrix is extracted by principal component analysis. The method is used to analyze the mechanism of high-temperature formaldehyde oxidation and high-temperature propane pyrolysis. Ranking of the elementary reactions allowed us to reduce significantly the original mechanisms and a detailed study of the results revealed the reaction structures and the major reaction paths of the species.
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  • 158
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    International Journal of Chemical Kinetics 21 (1989), S. 165-174 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The canonical formalism of the statistical adiabatic channel model is used to calculate limiting high pressure rate constants for the H + CH3 → CH4 recombination reaction on a recently reported analytic potential energy surface based on ab initio calculations. An effective adiabatic channel potential which incorporates the Gφφ matrix element of the twofold degenerate H3C—H transitional bending mode, quartic anharmonicity, and state selected mode coupling effects is implemented. The rate constants calculated over the temperature range 200-1000 K are in very good agreement with recent canonical variational transition state theory calculations performed on the same surface. The comparison with experimental results is also discussed.
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  • 159
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    International Journal of Chemical Kinetics 21 (1989), S. 193-206 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrolysis kinetics of the title compounds has been studied in a stirred-flow reactor over the temperature range 440-530°C and pressures between 5 and 14 torr. Benzyl t-butyl sulfide and phenyl t-butyl ether formed isobutene as product in over 98% yield, together with the corresponding benzyl thiol and phenol. The benzyl thiol decomposes to a large extent into hydrogen sulfide and bibenzyl. In the pyrolysis of phenyl t-butyl sulfide, the hydrocarbon products consisted of 80 ±5% isobutene plus 20% isobutane, while the sulfur containing products were thiophenol and diphenyl disulfide. Order one kinetics was observed for the consumption of the reactants. The first order rate coefficients, based on isobutene production, followed the Arrhenius equations: Benzyl t-butyl sulfide: \documentclass{article}\pagestyle{empty}\begin{document}$$k(s^{ - 1}) = 10^{13.82 \pm 0.41} \exp ( - 214 \pm 6{\rm kJ/mol }RT)$$\end{document} Phenyl t-butyl sulfide: \documentclass{article}\pagestyle{empty}\begin{document}$$k(s^{ - 1}) = 10^{12.03 \pm 0.39} \exp ( - 188 \pm 6{\rm kJ/mol }RT)$$\end{document} Phenyl t-butyl ether: \documentclass{article}\pagestyle{empty}\begin{document}$$k(s^{ - 1}) = 10^{14.30 \pm 0.21} \exp ( - 211 \pm 3{\rm kJ/mol }RT)$$\end{document}For benzyl t-butyl sulfide and phenyl t-butyl ether, the results suggest a unimolecular mechanism involving polar four center cyclic transition states. For phenyl t-butyl sulfide, the t-butyl-sulfur single bond fission mechanism is a parallel, less important process than the complex fission one.
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  • 160
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    International Journal of Chemical Kinetics 21 (1989) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 161
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    International Journal of Chemical Kinetics 21 (1989), S. 331-341 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following reactions: were studied over the temperature ranges 533-687 K, 563-663 K, and 503-613 K for the forward reactions respectively and over 683-763 K, for the back reaction. Arrhenius parameters for chlorine atom transfer were determined relative to the combination of the attacking radicals. The ΔHr°(1) = -3.95 ± 0.45 kcal mol-1 was calculated and from this value the ΔH∮(C2F5Cl) = -2.66.3 ± 2.5 kcal mol-1 and D(C2F5-Cl) = 82.0 ± 1.2 kcal mol-1 were obtained. Besides, the ΔHr°(2) was estimated leading to D(CF2ClCF2Cl) = 79.2 ± 5 Kcal mol-1. The bond dissociation energies and the heat of formation are compared with those of the literature. The effect of the halogen substitutents as well as the importance of the polar effects for halogen transfer processes are discussed.
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  • 162
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    International Journal of Chemical Kinetics 21 (1989) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 163
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    International Journal of Chemical Kinetics 21 (1989), S. 375-386 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic studies of the transfer of hydrogen from 9,10-dihydrophenanthrene to anthracene were done at 350°C in the liquid phase. Principal products were phenanthrene and 9,10-dihydroanthracene. Autocatalysis occurred at low extents of reaction, where H-transfer from 9,10-dihydroanthracene to anthracene caused an increase in free radical concentrations. At higher extents of reaction, 9,10-dihydroanthracene inhibited rates by diverting intermediate 9-hydrophenanthryl radicals back to reactants. A quantitative kinetic model based on literature rate and thermodynamic data fits the observations well. A key net reaction is the transfer of an H-atom from a radical (9-hydrophenanthryl) to a molecule (anthracene). It is shown that this process does not involve a free H-atom intermediate. The derived rate constant for this exothermic process (7.5 × 103 M-1 s-1) is considerably greater than that for the related, but thermoneutral H-transfer between anthracene moieties (120 M-1 s-1).
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  • 164
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    International Journal of Chemical Kinetics 21 (1989), S. 431-437 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rates of reaction for the alkaline hydrolysis of various hydroxamic acids in the presence of cetyltrimethylammonium bromide have been determined. Empirical reaction orders of zero, one-half, and one were found for the hydroxamic acids depending upon reaction conditions and substrate structure. N-methylhydroxamic acids exhibited only first-order kinetics. The results are consistent with the Michaelis-Menten rate equation.
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  • 165
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    International Journal of Chemical Kinetics 21 (1989), S. 465-476 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrogallol (1,2.3-benzentriol, 1) reacts with dioxygen in weakly alkaline solutions to form purpurogallin (2,3,4,6-tetrahydroxy-5H-benzocycloheptene-5-one, 2) which then reacts to form purpurogalloquinone (3) which then decays to a product absorbing at 440 nm. The formation of 3 requires 1.5 mol O2 per mol 1, and 1.0 mol per mol 2. No O2 is consumed during the decay of 3, and this reaction, being insensitive to O2 concentrations and the presence of both superoxide dismutase (SOD) and catalase, does not appear to be an oxidation. The first-order rate of decay of 3 decreases with increasing pH. 1 and 3 react at pH 9.0 with a second-order rate constant of ca. 100 M-1 s-1. SOD inhibits the oxidation of 1 and 2. Slight and variable apparent inhibition of the oxidation of 2 and 3 by SOD may be due to trace impurities in 2, but not contamination by 1. The peak concentration of 3 is attained more rapidly during the oxidation of 1 than during the oxidation of 2. A kinetic scheme based on parallel oxidation of 1 by dioxygen and superoxide, and it which the semiquinone of 1 oxidizes 2, is partially successful in simulating the observed kinetic behavior.
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  • 166
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    International Journal of Chemical Kinetics 21 (1989), S. 1-20 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for the measurement of relative rate constants for abstraction of hydrogen from ethylene at temperatures in the region of 750 K. The method is based on the effect of the addition of small quantities of propane and isobutane on the rates of formation of products in the thermal chain reactions of ethylene. On the assumption that methane and ethane are formed by the following reactions, measurements of the ratio of the rates of formation of methane and ethane in the presence and absence of the additive gave the following results: \documentclass{article}\pagestyle{empty}\begin{document}$$\log (k_7 /k_2) = (- 0.50 \pm 0.4) + (3200 \pm 1000)/2.3T$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log (k_8 /k_3) = (- 0.20 \pm 0.4) + (2800 \pm 1000)/2.3T$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log (k_{11} /k_2) = (- 0.97 \pm 0.4) + (4600 \pm 1000)/2.3T$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log (k_{12} /k_3) = (- 2.0 \pm 0.4) + (6300 \pm 1000)/2.3T$$\end{document} Values for k2 and k3 obtained from these ratios are compared with previous measurements.
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  • 167
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    International Journal of Chemical Kinetics 21 (1989), S. 1123-1129 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using a relative rate method, rate constants for the gas-phase reactions of the OH radical with 1- and 2-propyl nitrate, 1- and 2-butyl nitrate and 1-nitrobutane have been determined in the presence of one atmosphere of air at 298 ± 2 K. Using rate constants for the reactions of the OH radical with propane and cyclohexane of 1.15 × 10-12 and 7.49 × 10-12 cm3 molecule-1 s-1, respectively, following rate constants (in units of 10-12 cm3 molecule-1 s-1) were obtained: 1-propyl nitrate, 0.62; 2-propyl nitrate, 0.41; 1-butyl nitrate, 1.78; 2-butyl nitrate, 0.93; and 1-nitrobutane, 1.35. These rate constants are compared and discussed with the literature data.
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  • 168
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    International Journal of Chemical Kinetics 21 (1989), S. 561-574 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chemical kinetic model was constructed for the pyrolysis of butylbenzene. The mechanism was based on free radical reactions. All relevant reactions were considered, and a final selection of 60 reactions involving 29 molecules and free radicals was made. The rate constants and thermodynamic parameters were taken from the literature or estimated using accepted literature methods such as group additivity. The results from the model were compared to experimental rates and product selectivity for butylbenzene pyrolysis over a temperature range of 778 K to 868 K and to an experimental rate at 923 K. The rates agreed within a factor of two and were usually much closer. The experimental and theoretical yields of the major products, styrene, ethane, toluene, and propylene, agreed within two percentage points. The agreement for seven minor products was not quite as good, with the worst case being an overprediction of the yield of allylbenzene by a factor of 2.6.
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  • 169
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    International Journal of Chemical Kinetics 21 (1989), S. 611-619 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants have been determined for the reactions of SO4- with a series of alkanes and ethers. The SO4- radical was produced by the laser-flash photolysis of persulfate, S2O82-. For methane, only an upper limit of 1 × 106 M-1 s-1 could be determined. For ethane, propane, and 2-methylpropane, rate constants of 0.44, 4.0, and 10.5 × 107 M-1 s-1 were found. For ethyl and n-propyl ether, rate constants of 1.3 × 108 and 2.2 × 108 M-1 s-1 were found and for 1,4-dioxane and tetrahydrofuran, rate constants of 7.2 × 107 and 2.8 × 108 were obtained. The reaction of SO4- with allyl alcohol was also studied and found to have a rate constant of 1.4 × 109 M-1 s-1.
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  • 170
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    International Journal of Chemical Kinetics 21 (1989), S. 667-676 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constants for the reaction of NO3· with sulfur compounds in acetonitrile have been determined by the flash photolysis method. The rate constant for dimethyl sulfone (2.7 × 104 M-1s-1 at -10°C) is larger than that of the deuterium derivative, indicating that NO3· abstracts the hydrogen atom from dimethyl sulfone. In the case of dimethyl sulfide, the rate constant was evaluated to be 1.5 × 109 M-1 s-1 at -10°C; the transient absorption band attributable to the cation radical was observed after the decay of NO3·, suggesting the electron transfer reaction from the sulfide to NO3·. For diphenyl sulfide and dimethyl disulfide, the electron transfer reactions were also confirmed. For dimethyl sulfoxide, the reaction rate constant of 1.2 × 109 M-1 s-1 (at -10°C) was not practically affected by the deuterium substitution, suggesting that NO3· adds to sulfur atom forming (CH3)2Ṡ(O)-ONO2. On the other hand, for diphenyl sulfoxide, the electron transfer reaction occurs. By the comparison of these rate constants in acetonitrile solution with the reported rate constants in the gas phase, the change of the reaction paths was revealed.
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  • 171
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    International Journal of Chemical Kinetics 21 (1989), S. 703-714 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Radical reactions involving two or more intermediates and many mutual reaction channels may lead to the specific formation of one cross-reaction product if one species is rather persistent and if transient and persistent species are produced with equal rates. A previous kinetic analysis of the phenomenon revealed that the concentrations of the intermediates and the selectivities of product formation depend critically on the relative initiation rates. The present experimental ESR studies on systems involving simultaneously generated phenoxyl radicals as persistent and alkyl radicals as transient species confirm the predicted behavior. They also lead to absolute rate constants for reactions of alkyl with phenoxyl radicals and for hydrogen atom transfer from phenols to alkyl radicals.
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  • 172
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intermediate product of the reaction of MoOS2(S2CNR2)2 and PPh3 in dichloroethane has been detected by ESR spectroscopy. Two ESR signals have been observed at low temperature in the reaction system which was stopped by quenching it in liquid nitrogen. The g values are 2.020 ± 0.001 and 1.972 ± 0.001 respectively. The signal at g = 2.020 is attributed to a reaction intermediate with pentavalent molybdenum. A reaction mechanism has been proposed which is consistent with the observation of pentavalent molybdenum as the intermediate in the process of reaction.
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  • 173
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    International Journal of Chemical Kinetics 21 (1989), S. 21-29 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants and activation parameters of direct reaction of oxirane with certain alkyl-2-hydroxyethyl sulfides and/or successive oxyethylene adducts in the presence of basic catalyst were studied at temperatures 323-353 K. The reactions were found to be of the first order with respect to oxirane, sulfide, and catalyst concentrations. The kinetics are consistent with a termolecular mechanism.
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  • 174
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 175
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    International Journal of Chemical Kinetics 21 (1989), S. 233-243 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that kinetic data on the polymerization of acetylene to vinyl acetylene and benzene can be reconciled with the formation of a 1,4 biradical which can isomerize by a 1-3, H-atom shift to the molecular product. Since the biradicals have a negligibly small life-time in the system the overall process appears to be a concerted bimolecular reaction. The labile isomer CH2 = C: which had been suggested as being the reactive intermediate, is argued on energy considerations not to be a plausible intermediate.Data on the reverse pyrolysis of vinyl acetylene to acetylene are consistent with the model. Extending the model to butadiene explains the observed molecular nature of its decomposition to ethylene and acetylene.Reactions of other oligomers of acetylene are discussed.
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  • 176
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies of the kinetics of thermal unimolecular decomposition of methylcyclopentane, methylcyclohexane, ethynylcyclopentane, and ethynylcyclohexane have been carried out at temperatures in the range 861-1218 K using the technique of very low-pressure pyrolysis (VLPP). Multiple reaction pathways and secondary decomposition of primary products results in a complex array of reaction products. VLPP rate data (fall-off regime) were obtained for the overall decompositions and interpreted via the application of RRKM theory. The data for methylcyclopentane and methylcyclohexane were interpreted in terms of ring-opening bond fission pathways and bond fission to methyl and cycloalkyl radicals. By selecting Arrhenius parameters consistent with the analogous pathways in open-chain alkanes, a good fit to the overall decomposition is obtained. The data for ethynylcyclopentane and ethynylcyclohexane were interpreted in terms of ring-opening bond fission and alkyne to allene isomerization. The A factors for ring opening were based on known values for C-C fission in open-chain alkynes and the Arrhenius parameters for isomerization were chosen to be consistent with previously reported alkyne to allene isomerizations. The VLPP data are consistent with the following high-pressure rate expressions (at 〈 T 〉 = 1100 K) for the dominant primary reaction channel of ring opening adjacent to the substitutent group: \documentclass{article}\pagestyle{empty}\begin{document}$$\log (k/s^{ - 1} ) = (16.4 \pm 0.3) - (341 \pm 10)/\theta {\rm for methylcyclopentane,}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log (k/s^{ - 1} ) = (16.4 \pm 0.3) - (345 \pm 10)/\theta {\rm for methylcyclopentane,}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log (k/s^{ - 1} ) = (16.0 \pm 0.3) - (304 \pm 10)/\theta {\rm for ethynylcyclpentane, and}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log (k/s^{ - 1} ) = (16.0 \pm 0.3) - (303 \pm 10)/\theta {\rm for ethynylcyclohexane,}$$\end{document} where θ = 2.303RT kJ mol-. Comparison of the activation energies for the ethynyl-cycloalkanes with those for the methyl-cycloalkanes shows that the effect of the ethynyl substituent is consistent with the propargyl resonance energy. This evidence supports the assumption of a biradical mechanism for ring opening in these cycloalkanes.
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  • 177
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    International Journal of Chemical Kinetics 21 (1989), S. 297-314 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from Smoluchowski's hypothesis, a simple algorithm is developed in order to obtain the apparent rate constant at large values of time, t, with some physical and chemical processes, as in the case of diffusion controlled reactions. Some practical examples are illustrated, assuming nonuniform distribution function, space-dependent diffusion coefficient or short-range interaction leading to an asymptotic analytical expression of the form α + β/√t, where α and β are constants function of the system of interest.
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  • 178
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-chloro-3-aminopropanol was obtained in aqueous solution by mixing the amine with the hypochlorite. The first order decomposition kinetics of the N-chloramine in strongly alkaline media are explained by a mechanism in which the rate controlling step is the formation of an imine which is subsequently hydrolyzed. Spectrophotometry of the reaction in acid media showed that under these conditions dichloramines are formed: the second order experimental kinetics of this process are explained by a mechanism in which the rate-controlling step is a reaction between the protonated and free forms of the N-chloramine.
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  • 179
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    International Journal of Chemical Kinetics 21 (1989), S. 367-371 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The elimination kinetics of 2-chloropropionic acid have been studied over the temperature range of 320-370.2°C and pressure range of 79-218.5 torr. The reaction in seasoned vessel and in the presence of the free radical suppressor cyclohexene, is homogeneous, unimolecular, and obeys a first-order rate law. The dehydrochlorination products are acetaldehyde and carbon monoxide. The rate coefficient is expressed by the following Arrhenius equation: log k1(s-1) = (12.53 ± 0.43) - (186.9 ± 5.1) kJ mol-1 (2.303RT)-1. The hydrogen atom of the carboxylic COOH appears to assist readily the leaving chloride ion in the transition state, suggesting an intimate ion pair mechanism operating in this reaction.
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  • 180
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    International Journal of Chemical Kinetics 21 (1989), S. 399-421 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of oxidation of 2,2′-azinobis-(3-ethylbenzothiazole-6-sulphonate) (ABTS) by the inorganic peroxides, peroxomonosulphate, peroxodisulphate, peroxodiphosphate, and hydrogen peroxide were investigated in aqueous solution. The kinetics of formation of the radical cation, ABTS.+, on one-electron abstraction by these peroxides and the further reaction of ABTS.+ with higher concentrations of these peroxides at longer time scale were studied by following the growth and decay of the radical cation, ABTS.+ at 417 nm. The rate of formation of ABTS.+ was found to obey a total second-order, first-order each in [ABTS] and [peroxide], except for H2O2, which reacted through Michaelis-Menten kinetics. All the peroxides investigated were found to react with ABTS.+; however peroxodisulphate alone oxidized ABTS.+ to the dication (ABTS++), the other peroxides reacted via ionic mechanism, probably forming sulphoxide and sulphone as products. The kinetics of decay of the radical cation, ABTS.+, was also found to follow a total second-order, first-order each in [ABTS.+] and [peroxide], except peroxodiphosphate the reaction of which obeyed Michaelis-Menten kinetics. The effect of pH and temperature were also investigated in all the systems and the kinetic and thermodynamic parameters were evaluated and discussed with suitable reaction mechanisms.
    Additional Material: 12 Ill.
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  • 181
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate coefficients were calculated for vibrational relaxation and collision-induced dissociation of ground state xenon fluoride in neon at temperatures between 300 and 1000 K for each of nine vibrational levels. These coefficients were calculated using a pairwise additive potential energy surface, which consists of a Morse function for the XeF interaction and Lennard-Jones functions for the NeXe and NeF interactions. Rate coefficients are provided for both temperature and v- dependences. The vibrational relaxation and dissociation processes occur by multiquanta transitions. Dissociation can take place from all v-levels provided that the internal energy of the XeF molecule is close to the rotationless dissociation limit. The order of increase effectiveness of the various forms of energy in promoting dissociation in XeF was found to be translation-rotation-vibration. At room temperature, neon atoms were found to be more efficient than helium atoms in the dissociation processes; helium atoms were found to be more efficient than neon atoms in the vibrational relaxation of XeF. Strong vibration-rotation coupling in both vibrational relaxation and in the dissociation processes is demonstrated.
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  • 182
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    International Journal of Chemical Kinetics 21 (1989), S. 1049-1067 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The high temperature kinetics of NH in the pyrolysis of isocyanic acid (HNCO) have been studied in reflected shock wave experiments. Time histories of the NH(X3Σ-) radical were measured using a cw, narrow-linewidth laser absorption diagnostic at 336 nm. The second-order rate coefficients of the reactions: were determined to be: \documentclass{article}\pagestyle{empty}\begin{document}$$k_{1{\rm a}} = 9.84\,\, \times \,\,10^{15} \,\,\exp (- 43000/T,{\rm K})\,\,\,\,\,\,(f = 0.65,F = 1.50)\,\,\,\,\,\,T = 1830 - 3340\,\,{\rm K,}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm 2} = 5.1\,\, \times \,\,10^{13} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(f = 0.7,F = 1.3)\,\,\,\,\,\,T = 2070 - 2730\,\,{\rm K,}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm 3} = 2.65\,\, \times \,\,10^{14} \,\,\,\exp (- 38000/T,{\rm K})\,\,\,\,\,\,(f = 0.5,F = 1.4)\,\,\,\,\,\,T = 3140 - 3320\,\,{\rm K,}$$\end{document} cm3-mol-1-s-1, where f and F define the lower and upper uncertainty limits, respectively. The data for k1a are somewhat better fit by: \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm 1a}} = 3.26\,\, \times \,\,10^{35} T^{ - 5.11} \,\,\exp (- 55300/T,{\rm K})\,\,\,{\rm cm}^{\rm 3} {\rm - mol}^{{\rm - 1}} {\rm - s}^{{\rm - 1}} .$$\end{document}
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  • 183
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    International Journal of Chemical Kinetics 21 (1989), S. 1095-1100 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics and products of the decomposition of 9-diazofluorene by tris (p-bromophenyl) aminium hexachloroantimonate in acetonitrile solvent has been investigated. The reaction is first order with respect to the concentration of both 9-diazofluorene and tris (p-bromophenyl) aminium hexachloroantimonate. A reaction mechanism has also been proposed.
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  • 184
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    International Journal of Chemical Kinetics 21 (1989), S. 1131-1139 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pressure-jump method has been used to determine the rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with cinchomeronate in aqueous solution at zero ionic strength. The forward and reverse rate constants obtained are kf = 2.27 × 106 M-1 s-1 and kr = 3.81 × 101 s-1 for the nickel(II) complex and kf = 1.23 × 107 M-1 s-1 and kr = 2.66 × 102 s-1 for the cobalt(II) complex at 25°C. The activation parameters of the reactions have also been obtained from the temperature variation study. The results indicate that the rate determining step of the reaction is a loss of a water molecule from the inner coordination sphere of the cation for the nickel(II) complex and the chelate ring closure for the cobalt(II) complex. The influence of the pyridine ring nitrogen atom of the cinchomeronate ligand on the complexation of cobalt(II) ion is also discussed.
    Additional Material: 4 Tab.
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  • 185
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    International Journal of Chemical Kinetics 21 (1989), S. 485-498 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of the hydroxyl radical, OH, with several reactants have been studied near 1200 K in shock tube experiments in which UV absorption was used to monitor the OH concentration. The values of the rate coefficients were found to be 2.7 × 1012, 2.6 × 1012, 2.8 × 1013, and 1.26 × 1013 cm3/mol-s for the reactions of OH with hydrogen, methane, cyclopentane, and isobutane, respectively. These measured values are compared with previous experimental results and transition-state theory calculations.
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  • 186
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    International Journal of Chemical Kinetics 21 (1989), S. 535-546 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The near U-V photolysis of t-butyl nitrite has been studied over the temperature range 303-393 K. Under these conditions t-butyl nitrite was shown to be a very clean photochemical source of t-butoxy radicals. This allows a study of the decomposition of the t-butoxy radical to be made over this temperature range (3). Extrapolation of the rate constants k3 to high pressure and combination with our previous thermal data give the results: \documentclass{article}\pagestyle{empty}\begin{document}$$k_3 (\infty)/{\rm s}^{{\rm - 1}} = 10^{14.04 \pm 0.37} \exp (- 7519 \pm 70.5/T)$$\end{document}
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  • 187
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    International Journal of Chemical Kinetics 21 (1989), S. 575-591 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title reaction has been studied in a static quartz reaction vessel between 587 and 658 K at pressures between 40 and 152 torr. The dehydrochlorination is the only significant reaction and is autoaccelerated by the produced HCl. Numerical modelling indicates that the Rice-Herzfeld mechanism, generally used for describing the pyrolysis of halogenated ethanes, has to be completed in the case of CC13CH3 with additional transfer reactions converting “dead” radicals into chain carriers and vice-versa. The numerical simulation fits the experimental results, in the absence as well as in the presence of different amounts of added HCl. The dehydrochlorination is also accelerated by the addition of CCl4, which can be explained in terms of additional elementary steps involving · CCl3 radicals.
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  • 188
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    International Journal of Chemical Kinetics 21 (1989), S. 643-666 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Propyne (p-C3H4) or allene (a-C3H4) mixtures, highly diluted with Ar, were heated to the temperature range 1200-1570 K at pressures of 1.7-2.6 atm behind reflected shock waves. The thermal decompositions of propyne and allene were studied by both measuring the profiles of the IR emission at 3.48 μm or 5.18 μm and analyzing the concentrations of reacted gas mixtures. The mechanism and the rate constant expressions were discussed from both the profiles and the concentrations of reactant and products obtained. The rate constant expressions for reactions, (1) p-C3H4 → a-C3H4, (-1) a-C3H4 → p-C3H4, and (5) p-C3H4 + H → CH3 + C2H2 were evaluated.
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  • 189
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    International Journal of Chemical Kinetics 21 (1989), S. 621-633 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetics of oxidation of thiocyanate ion (NCS-) by iodine monochloride and iodine has been studied in aqueous perchloric acid medium. The rates of oxidations followed the rate laws: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {- \frac{{d[{\rm ICl]}}}{{dt}} = \frac{{k[{\rm ICl][NCS}^ -][{\rm H}^ +]}}{{l + {\rm K[NCS}^ -][{\rm H}^ +]}}} \\ {- \frac{{d[{\rm I}_{\rm 2}]}}{{dt}} = \frac{{k'[{\rm I}_{\rm 3} ^ -][{\rm NCS}^ -][{\rm H}^ +]}}{{[{\rm I}^ -][1 + {\rm K'[H}^ +]]}}{\rm at low [H}^ +]} \\ {{\rm and} - \frac{{d[{\rm I}_{\rm 2}]}}{{dt}} = \frac{{k''[{\rm I}_{\rm 2}]}}{{k'' + [{\rm H}^ +][{\rm I}^ -]}}{\rm at high [H}^ +]} \\ \end{array} $$\end{document} Variations in ionic strength and dielectric constant of the medium had little effects on the rates of reactions with both the oxidants. Mechanisms consistent with the observed rate laws have been suggested. Rate limiting steps have been identified and the constants of some of these steps have been evaluated by varying [NCS-] at each temperature. Activation parameters were computed from the Arrhenius plots. The rate constants predicted from the rate law as [NCS-], and [H+], varied in iodine monochloride oxidation, are in good agreement with the experimental values providing support to the proposed mechanism.
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  • 190
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    International Journal of Chemical Kinetics 21 (1989), S. 689-701 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of propane was studied behind reflected shock waves over the temperature range 1100-1450 K and the pressure range 1.5-2.6 atm, by both monitoring the time variations of absorption at 3.39 μm and analyzing the concentrations of the reacted gas mixtures. The rate constants of the elementary reactions were discussed from the results. The rate constant expressions, k1 = 1.1 × 1016 exp (-84 kcal/RT) s-1 and k4 = 9.3 × 1013 exp(-8 kcal/RT) cm3 mol-1 s-1, of reactions C3H8 → CH3 + C2H5 and C3H8 + H → n-C3H7 + H2 were evaluated, respectively.
    Additional Material: 7 Ill.
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  • 191
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    International Journal of Chemical Kinetics 21 (1989), S. 715-727 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The UV absorption spectrum and the kinetics of the self combination reaction of the CCl3 radical were studied by flash photolysis in the temperature range 253-623 K. Experiments were performed at the atmospheric pressure, except for a few runs at the highest temperatures, which were performed between 30 and 760 torr. CCl3 radicals were generated by flash photolysis of molecular chlorine in the presence of chloroform. The UV spectrum exhibits a strong unstructured band between 195 and 260 nm with a maximum at 211 ± 2 nm. The absorption cross section, measured relative to σ(HO2), is σ(CCl3) = (1.45 ± 0.35) × 10-17 cm2 molecule-1 at the maximum. This value takes into account the uncertainty in σ(HO2) which was taken equal to (4.9 ± 0.7) × 10-18 cm2 molecule-1. The absolute rate constant for the CCl3 mutual combination was determined by computer simulation of the transient decays. The rate constant, which exhibits a slight negative temperature coefficient, can be expressed as: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_6 = (3.3 \pm 0.8) \times 10^{- 12} (T/298)^{- 1.0 \pm 0.2} {\rm cm}^{\rm 3} {\rm molecule}^{- 1} {\rm s}^{- 1} {\rm at 760 torr}{\rm.} $$\end{document}The study of the pressure dependence showed that only a slight fall-off behavior could be observed at the highest temperature (623 K). This result was corroborated by RRKM calculations which showed that the rate constant is at the high pressure limit under most experimental conditions below 600 K.
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  • 192
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    International Journal of Chemical Kinetics 21 (1989), S. 765-774 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pulsed laser photolysis/laser-induced fluorescence (LIF) is utilized to measure absolute rate constants of CH radical reactions as a function of temperature and pressure. Multiphoton dissociation of CHBr3 at 266 nm is employed for the generation of CH (X2Π) radicals. The CH radical relative concentration is monitored by exciting fluorescence on the R1(2) line of the (A2Δ - X2Π) transition at 429.8 nm. A resistively heated cell allows temperature studies to be performed from room temperature to ≈670 K. The following Arrhenius equations are derived: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}\,{\rm + }\,{\rm N}_{\rm 2} {\rm O,}\,\,\,\,\,\,\,\,k = (1.59 \pm 0.20)\, \times \,\,10^{ - 11} \,\,\exp [(500 \pm 45)/T]{\rm cm}^{\rm 3} {\rm s}^{{\rm - 1}};$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}\,{\rm + }\,{\rm SO}_{\rm 2} {\rm ,}\,\,\,\,\,\,\,\,k = (1.32 \pm 0.17)\, \times \,\,\,10^{ - 10} \,\,\exp [(250 \pm 45)/T]\,\,{\rm cm}^{\rm 3} {\rm s}^{{\rm - 1}};$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}\,{\rm + }\,{\rm OCS,}\,\,\,\,\,\,\,\,k = (1.99 \pm 0.11)\, \times \,\,\,10^{ - 10} \,\,\exp [(190 \pm 20)/T]\,\,{\rm cm}^{\rm 3} {\rm s}^{{\rm - 1}};$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}\,{\rm + }\,{\rm CS}_{\rm 2} {\rm ,}\,\,\,\,\,\,\,\,k = (3.49 \pm 0.36)\, \times \,\,\,10^{ - 10} \,\,\exp [- (40 \pm 35)/T]\,\,{\rm cm}^{\rm 3} {\rm s}^{{\rm - 1}};$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}\,{\rm + }\,{\rm SF}_{\rm 6} {\rm ,}\,\,\,\,\,\,\,\,k 〈 5\,\,\, \times \,\,\,10^{ - 17} {\rm cm}^{\rm 3} {\rm s}^{{\rm - 1}} .$$\end{document} With the exception of SF6, the reactions of sulfur containing species proceed at rates that are near the theoretical gas kinetic collision frequency. Additionally, these reactions all have activation energies that are near zero or slightly negative. These observations are consistent with an insertion-decomposition mechanism being dominant under these conditions.
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  • 193
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    International Journal of Chemical Kinetics 21 (1989), S. 847-858 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Second order rate constants for C2H2 or C2D2 polymerizations into vinylacetylene and higher CnHn products have been measured in a static reactor by dynamic mass spectrometry between 770-980 K. They are nearly identical within experimental error (±50%). It is shown that these results are consistent with the participation of thermally equilibrated vinylidene H2C = C: as a reactive intermediate: since this assumption only introduces a modest reverse equilibrium isotope effect (KiH/KiD ca. 0.48 in this range) into overall rate constants. At the same time they seem to discriminate in general against alternative mechanisms in which the required H-atom transfers take place in rate determining steps. Present evidence, in conjunction with an updated analysis of relevant issues such as experimental and theoretical vs. termochemical estimates of the heat of formation of H2C=C:, the nature of the transition states of singlet vinylidene addition reactions and the likelihood of discrete biradical intermediates in C2H2 dimerization, seems to lend further support to the notion that acetylene behaves as a singlet carbene at high temperatures.
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  • 194
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements from previous studies have shown that when hydroxyl radicals react with various chlorinated hydrocarbons under atmospheric conditions, free chlorine atoms can be produced. In one such study (Edney et al., [3]) from an analysis of the rate equations under a strict set of assumptions, Cl-atom yields could be inferred. Since the approach was indirect, a more direct method for obtaining these yields has been developed. The technique described in this study involves scavenging Cl atoms produced by the reaction (using ethylene or propylene as the scavenger) and then measuring the yield of the stable chlorinated product generated. Cl-atom yields were determined for allyl chloride, vinyl chloride, vinylidene chloride, trichloroethylene, and benzyl chloride. The experiments were performed by irradiating mixtures of CH3ONO/NO/chlorinated hydrocarbon/alkene in air in 150-L Teflon chambers. The yields for the reaction of Cl atoms with the alkenes generating the stable products were determined in seperate experiments. Yields for the formation of Cl atoms upon reaction with hydroxyl radicals are as follows (with 1 σ deviation): allyl chloride: 0.37 ± 0.10, vinyl chloride: 0.04 ± 0.01, vinylidene chloride: 0.23 ± 0.09, trichloroethylene: 0.63 ± 0.34, and benzyl chloride: 0.08 ± 0.03.
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  • 195
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    International Journal of Chemical Kinetics 21 (1989), S. 959-966 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transient diaryl disulfide radical anions (RSSR-) were produced in nonaqueous solutions at room temperature by the flash photolysis of a solution of arylthiolate ion pair in the presence of the excess corresponding disulfide. The transient spectra were almost identical with those obtained from γ-radiolysis of the disulfides in 77 K 2-methyl-tetrahydrofuran (MTHF) glassy matrix. The spectra of disulfide radical anions in nonaqueous solutions were changed by cations, solvents, and para-substituents depending on the ion pair properties. The tighter ion pairs showed a shift of absorption band to the shorter wavelength. The disulfide radical anions decay by a unimolecular dissociation reaction to yield thiolate anion and thiyl radical. The decay kinetics were first-order in the initial time region. The rate constants obtained were changed by the counter cations in the order Na+ 〉 K+ 〉 Cs+ 〉 Li+, and by solvents. The tighter ion pairs of the disulfide radical anions showed faster dissociation reaction. This is due to stabilization of a transition state with the counter cation.
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  • 196
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    International Journal of Chemical Kinetics 21 (1989), S. 1015-1027 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal reaction of CH2O with NO2 has been investigated in the temperature range of 393-476 K by means of FTIR product analysis. Kinetic modeling of the measured CH2O, NO, CO, and CO2 concentration time profiles under varying reaction conditions gave rise to the rate constants for the following key reactions: and The error limits shown represent only the scatter (±1 σ) of the modeled values. In the modeling, the total rate constant for the CHO + NO2 reaction, k2 + k3, was not varied and the value reported by Gutman and co-workers (ref. [8]) was used for the whole temperature range investigated here. The proposed reaction mechanism, employing these newly established rate constants, can quantitively account for nearly all measured product yields, including the [CO]/([CO] + [CO2]) ratios reported by earlier workers.
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  • 197
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    International Journal of Chemical Kinetics 21 (1989), S. 1077-1089 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fourier transform infrared spectroscopy was used to identify and quantify products of the self reaction of ethylperoxy radicals, C2H5O2, formed in the photolysis of Cl2/C2H6 mixtures in 700 torr total pressure of synthetic air at 295 K. From these measurements, branching ratios for the reaction channels of k1a/(k1a + k1b) = 0.68 and k1c/(k1a + k1b + k1c) ≤ 0.06 were established. Additionally, using the relative rate technique, the rate constant for the reaction of Cl atoms with C2H5OOH was determined to be (1.07 ± 0.07) × 10-10 × cm3 molecule-1 s-1. Results are discussed with respect to the previous kinetic and mechanistic studies of C2H5O2 radicals.
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  • 198
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    International Journal of Chemical Kinetics 21 (1989), S. 1101-1112 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas phase reaction of OH radicals with dimethyl sulfide (CH3SCH3, DMS) has been studied using both an absolute and a relative technique at 295 ± 2 K and a total pressure of 1 atm. The absolute rate technique of pulse radiolysis combined with kinetic spectroscopy was applied. Using this technique a rate constant of (3.5 ± 0.2) × 10-12 cm3 molecule-1 s-1 was obtained. For the relative rate method, rate constants for the reaction of OH with DMS were found to increase with increasing concentrations of added NO. These results are compared with the large body of kinetic and mechanistic data previously reported in the literature.
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  • 199
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    International Journal of Chemical Kinetics 21 (1989), S. 1141-1152 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase reaction of methyl vinyl ketone with the OH radical, in the presence of NOx, was investigated at 298 ± 2 K and atmospheric pressure of air. Glycolaldehyde and methylglyoxal were observed to be the major products, with a combined yield of 0.89 ± 0.16. The sum of the yields of the two other main products, formaldehyde and peroxyacetyl nitrate, were found to be essentially unity. The product yield data for glycolaldehyde and methylglyoxal indicate that OH radical addition to the terminal carbon atom of the 〉C=C〈 bond accounts for 72 ± 21% of the overall reaction, with the remaining 28 ± 9% proceeding via addition to the inner carbon atom of the double bond.
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  • 200
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    International Journal of Chemical Kinetics 21 (1989), S. 207-218 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photo-oxidation of n-heptane in synthetic air containing methyl nitrite and nitric oxide has been ivestigated in an atmospheric flow reactor. By measuring the total yields of heptyl nitrate products, relative to the depletion of the n-heptane, the rate constant ratio, k3b/k3a has been determined for the reactions: Over the temperature range 253-325 K and at a total pressure of 730 Torr, the following relative Arrhenius equation has been obtained from the present study together with literature data: \documentclass{article}\pagestyle{empty}\begin{document}$$k_{3b} /k_{3a} = (1.4 \pm 1.1) \times 10^{ - 3} \exp [1640 \pm 250)/T]$$\end{document} These results confirm that the formation of alkyl nitrates from the photo-oxidation of n-alkanes arise from a primary reaction between the alkylperoxy radicals and nitric oxide. Furthermore the present experiments show that the lifetime of the intermediate in this type of reaction, presumed to be an alkyl peroxynitrite, ROONO, must be less than a few seconds.
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