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1.
The initiation reaction of the polymerization of α-methylstyrene by trityl tetrachloroferate and tritylhexachloroantimonate in 1,2-dichloroethane at 20°C was studied. The rate constants were 14 × 10?3 and 27 × 10?3 L mol?1s?1, respectively. The dissociation constants of tritylterachloroferate (Kd = 0.88 × 10?4M?1) and tritylhexachloroantimonate (Kd = 2.64 × 10?4M?1) was determined. The effect of electron acceptors and donors on the dissociation equilibrium and initiation rate was investigated. It was shown that in strongly dissociated ion pairs such as stable carbenium salts the electron donors and acceptors have no appreciable effect on the magnitude of the dissociation. The temperature dependence of the rate constants in the ?20–+20°C range yielded the following thermodynamic parameters for trityltetrachloroferate: Ei = 8.54 kcal/mol; A = 3.2 × 104 mol?1s?1; ΔH* = 8 kcal/mol; and S* = ?39.8 eu.  相似文献   

2.
The very low pressure reactor (VLPR) technique has been used to measure the bimolecular rate constant of the title reaction at 300 K. The rate constant is given by log k1 (1/mol s) = (11.6 ± 0.4) ? (5.9 ± 0.6)/θ the equilibrium constant has also been measured at the same temperature and is given by K1 = (5.6 ± 1) × 10?3 and hence log k?1 (1/mol s) = 9.5 ± 0.1. The results show that the reaction Br + t? C4H9 → HBr + i? C4H8 is unimportant under the present experimental conditions. Assigning the entropy of t-butyl radical to be 74 ± 2 eu which is in the possible range, the value of K1 gives ΔH (t-butyl) = 9.1 ± 0.6 kcal/mol?1. This yields for the bond dissociation, DH° (t-butyl-H) = 93.4 ± 0.6 kcal/mol. Both of these values are found to be in good agreement with recent VLPP studies.  相似文献   

3.
The CL spectra of the title reactions and their pressure dependences have been studied over the 5 × 10?6 ? 5 × 10?3 torr range in a beam-gas experiment. In the Sm + N2O, O3 and Yb + O3 reactions simple bimolecular formation of the short lived (radiative lifetime τR < 3 × 10?6 s) MO* emitters dominates the entire pressure range. In the other systems Sm + (F2, Cl2), Yb + (F2, Cl2) the CL spectra are strongly pressure dependent, indicating extensive energy transfer from long-lived intermediates. Reaction mechanisms are suggested. The quantum yields Φ, obtained by calibrating relative quantum yields with Dickson and Zare's absolute value for Sm + N2O [Chem. Phys. 7 (1975) 367], range from Φ = 2.3% (for Sm + F2, the most efficient reaction) down to Φ = 0.005% for Yb + Cl2. The following lower limit estimates were obtained for the product dissociation energies from the short wavelength CL cutoffs: D00(SmF) ? 121.3 ± 2.4 kcal/mole, D00(SmCl) ? ? 100 ± 3 kcal/mole, D00(YbO) ? 94.2 ± 1.5 kcal/moie, D00(YbF) ? 123.7 ± 2.3 kcal/mole.  相似文献   

4.
Sodium thiophenoxide initiated the polymerization of methyl methacrylate in polar aprotic solvents (DMF, DMSO, HMPA). The active species that initiated the polymerization of the monomer was found by spectrophotometric measurements and by the sodium fusion method to be sodium thiophenoxide itself. The activation energy for the polymerization of the monomer in DMF solvent obtained was E = 3.4 kcal/mole below 30°C, and E = ?3.3 kcal/mole above the temperature. The phenomena were reasoned as the result of the formation of two active species: a solvent-separated ion pair and a contact ion pair. The effects of counterions on the reactivity of thiophenoxide increased with increasing electropositivity of the metals: Li < Na < K. Sodium phenoxide, the oxygen analog of thiophenoxide, was also found to initiate the polymerization of the monomer in the solvents. The relative reactivity of thiophenoxide to phenoxide for the monomer in HMPA at 30°C was thus determined: phenyl-SNa > phenyl-ONa. The relative effect of the polar aprotic solvents on the reactivity of thiophenoxide was also as follows: HMPA > DMF > DMSO. The kinetic studies were made by the graphical evaluation of rate constants. The following results were obtained for the monomer at 20°C in DMF solvent: Kp = 3.5 × 102 1./mole-hr and Kt = 9.8 × 10?2/hr.  相似文献   

5.
The reaction of tetramethyl-1,2-dioxetane ( 1 ) and triphenylphosphine ( 2 ) in benzene-d6 produced 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane ( 3 ) in ?90% yield over the temperature range of 6–60°. Pinacolone and triphenylphosphine oxide ( 4 ) were the major side products [additionally acetone (from thermolysis of 1 ) and tetramethyloxirane ( 5 ) were noted at the higher temperatures]. Thermal decomposition of 3 produced only 4 and 5 . Kinetic studies were carried out by the chemiluminescence method. The rate of phosphorane was found to be first order with respect to each reagent. The activation parameters for the reaction of 1 and 2 were: Ea ? 9.8 ± 0.6 kcal/mole; ΔS = ?28 eu; k30° = 1.8 m?1sec?1 (range = 10–60°). Preliminary results for the reaction of 1 and tris (p-chlorophenyl)phosphine were: Ea ? 11 kcal/mole, ΔS = ?24 eu, k30° = 1.3 M?1sec?1 while those for the reaction of 1 and tris(p-anisyl)phosphine were: Ea ? 8.6 kcal/mole, ΔS = ?29 eu, k30° = 4.9 M?1 sec?1.  相似文献   

6.
It was established that the cytosine·thymine (C·T) mismatched DNA base pair with cis‐oriented N1H glycosidic bonds has propeller‐like structure (|N3C4C4N3| = 38.4°), which is stabilized by three specific intermolecular interactions–two antiparallel N4H…O4 (5.19 kcal mol?1) and N3H…N3 (6.33 kcal mol?1) H‐bonds and a van der Waals (vdW) contact O2…O2 (0.32 kcal mol?1). The C·T base mispair is thermodynamically stable structure (ΔGint = ?1.54 kcal mol?1) and even slightly more stable than the A·T Watson–Crick DNA base pair (ΔGint = ?1.43 kcal mol?1) at the room temperature. It was shown that the C·T ? C*·T* tautomerization via the double proton transfer (DPT) is assisted by the O2…O2 vdW contact along the entire range of the intrinsic reaction coordinate (IRC). The positive value of the Grunenberg's compliance constants (31.186, 30.265, and 22.166 Å/mdyn for the C·T, C*·T*, and TSC·T ? C*·T*, respectively) proves that the O2…O2 vdW contact is a stabilizing interaction. Based on the sweeps of the H‐bond energies, it was found that the N4H…O4/O4H…N4, and N3H…N3 H‐bonds in the C·T and C*·T* base pairs are anticooperative and weaken each other, whereas the middle N3H…N3 H‐bond and the O2…O2 vdW contact are cooperative and mutually reinforce each other. It was found that the tautomerization of the C·T base mispair through the DPT is concerted and asynchronous reaction that proceeds via the TSC·T ? C*·T* stabilized by the loosened N4? H? O4 covalent bridge, N3H…N3 H‐bond (9.67 kcal mol?1) and O2…O2 vdW contact (0.41 kcal mol?1). The nine key points, describing the evolution of the C·T ? C*·T* tautomerization via the DPT, were detected and completely investigated along the IRC. The C*·T* mispair was revealed to be the dynamically unstable structure with a lifetime 2.13·× 10?13 s. In this case, as for the A·T Watson–Crick DNA base pair, activates the mechanism of the quantum protection of the C·T DNA base mispair from its spontaneous mutagenic tautomerization through the DPT. © 2013 Wiley Periodicals, Inc.  相似文献   

7.
Rate constants for the tri-n-butyltin radical ( Sn · ) induced decomposition of a number of peroxides have been measured in benzene at 10°C. The values range from ~100 M?1 sec?1 for di-t-butyl peroxide to 2.6 × 107 M?1 sec?1 for di-t-butyl diperoxyisophthalate. The majority of the peroxides, including diethyl peroxide, diacetyl peroxide, and t-butyl peracetate, have rate constants of ~105 M?1 sec?1. It is shown that di-n-alkyl disulfides are ten times as reactive toward Sn · as di-n-alkyl peroxides, although the exothermicities of these reactions are ~15 and ~39 kcal/mole, respectively. The enhanced reactivity of the disulfides is attributed to the easier formation of an intermediate or transition state with 9 electrons around sulfur, compared with an analogous species with 9 electrons around oxygen. The following bond strengths (kcal/mole) have been estimated: D[ Sn ? OR] = 77; D[ Sn ? H] = 82; D[ Sn ? SR] = 83; and D[ Sn ? OC(O)R] = 86, where R = alkyl. Rate constants for reaction of Sn · with some benzyl esters have also been measured. It has been found that t-butoxy radicals can add to benzene and abstract hydrogen from benzene at ambient temperatures.  相似文献   

8.
Measurements of the D(R? NO) bond strength in some C-nitrosocompounds have been made using an electron impact method. The appearance potential of the radical ion (R+) has been determined, the D(R? NO) bond energy being obtained from the relation The values obtained are: D(C6H5? NO) = 41 kcal/mole, D(t-C4H9? NO) = 34 kcal/mole, D(t-C5H11? NO) = 36 kcal/mole and D(i-C3H7? NO) = 36.5 kcal/mole. These values are in good agreement with the numerous estimations of Benson and coworkers and confirm that the C? N bond strength in C-nitrosocompounds is very much less than in nitrocompounds or in amines.  相似文献   

9.
Chemically activated ethane, with an excitation energy of 114.9 ± 2 kcal/mole, was formed by reaction with methane of excited singlet methylene radicals produced by the 4358 Å photolysis of diazomethane. A decomposition rate constant of (4.6 ± 1.2) × 109 sec?1 was measured for the chemically activated ethane. This result agrees, via RRKM theory, with most other chemically activated ethane data, and the result predicts, via RRKM and absolute rate theory for E0 = 85.8 kcal/mole, E* = 114.9 kcal/mole, and kE = 4.6 × 101 sec?1, a thermal A-factor at 600°K of 1016.6±0.2 sec?1, in approximate agreement with the more recent experimental values. Combining 2 kcal/mole uncertainties in E0 and E* with the uncertainty in our rate constant yields an A-factor range of 1016.6±0.7 sec?1. It is emphasized that this large uncertainty in the A-factor results from an improbable combination of uncertainty limits for the various parameters. These decomposition results predict, via absolute rate theory (with E0(recombination) = 0) and statistical thermodynamic equilibrium constants, methyl radical recombination rates at 25°C of between 4.4 × 108 to 3.1 × 109 l.-mole?1-sec?1, which are 60 to 8 times lower, respectively, than the apparently quite reliable experimental value. A value of E0(recombination) greater than zero offers no improvement, and a value less than zero would be quite unusual. Activated complexes consistent with the experimental recombination rate and E0(recombination) = 0 greatly overestimate the experimental chemical activation and high pressure thermal decomposition rate data. Absolute rate theory as it is applied here in a straightforward way has failed in this case, or a significant amount of internally consistent data are in serious error. Some corrections to our previous calculations for higher alkanes are discussed in Appendix II.  相似文献   

10.
A dilatometric technique was used to obtain conversion–time data for the polymerization of acrylamide initiated by potassium persulfate in water. The results are summarized by the empirical rate expression, ?d[M1]/dt = Rp = k1.25[K2S2O8]0.5[M1]1.25, and k1.25 = 1.70 × 1011 exp {?16,900/RT} 1.0.75/mole?0.75-min. Persulfate was varied over the range 9.5 × 10?4 to 5.2 × 10×2 mole/l., and initial monomer concentration [M1] was varied from 0.05 to 0.4 mole/l. The temperature range was 30?50°C. Results of analysis of the kinetics and energetics of the polymerization favor a cage-effect theory rather than a complex-formation theory to explain the order with respect to monomer.  相似文献   

11.
Abstract

Using elementary analysis, NMR on 3 1P and 1H nuclei, and electroconductivity methods, the acrylonitrile, methacrylonitrile, formaldehyde, and β-propiolactone anionic polymerization in the presence of triethylphosphine is shown to follow the macrozwitterion mechanism: quartary phosphonium being on one end of a polymer chain and the growing anion on the other. The number of covalent bonds through the whole polymer chain between charges forming the active center increases with the propagation reaction. The active centers stationary concentration in the system is low when connected with both the slow initiation reaction and with the fast active centers termination reaction. Thus the ion interaction of different growing polymer chains can be ignored. The active centers parts occurring in the form of ion pairs (the ends are near and form the “cyclic”) and of free ions (the ends are separated) are determined by the monomolecular equilibrium, and its constant depends upon the macro-zwitterion polymerization degree Kd (n) = Kd (I)n3/2. Such constant depends upon the chain length affords the macrozwitterion self-accelerated propagation with its length, as the free ion reactivity is more than that of ion pairs. The self-accelerated chain propagation effect shows up as an increase of polymerization initial rate order and polymer molecular weight in the monomer concentration. This effect can be avoided by the introduction of electrolyte into the system, which dissociates into ions and transforms all cyclic ion pairs into the linear form, the latter dissociating independently of chain length. The strict mathematical analysis of stationary and nonstationary polymerization kinetics made it possible to determine all the elementary constants separately: Ki = 5.6 × 10?4 liters/ (mole) (min); K- = 2.5 × 104 liter/ (mole) (min); K± = 2.0 liters/ (mole) (min); Kt = 0.84/min; Kt 1 = 4/min; Kd (I) = 10?4; K3 = 0.07 × 10?4 mole/liter.  相似文献   

12.
A procedure to calculate the quantum mechanical transition probability of a unimolecular primary chemical process, A?A + e? is investigated for the circumstance where A? and A have different numbers of vibrational and rotational degrees of freedom (one is linear, the other not). A procedure is introduced to deal with the coupling between the vibrational and rotational motions. The proposed method was applied to calculating the lifetimes of CO2˙? and N2O˙? in the gas phase. The geometry optimizations and frequency calculations for CO2, CO2˙?, N2O, and N2O˙? are performed at HF, MP2, and QCISD(T) levels with 6-31G* or 6–31+G* basis sets, in order to obtain reliable geometric and spectroscopic information on these systems. Lifetimes are calculated for several of the lower vibrational–rotational states of the anions, as well as for the Boltzmann distribution of states at 298 K. The lifetime of the lowest vibrational–rotational state of CO2˙?, is 1.03 × 10?4 s, and of the lowest vibrational state with rotational levels weighted by Boltzmann distribution at 298 K, 1.50 × 10?4 s. These values are in good agreement with the experimental number, 9.0 ± 2.0 × 10?5 s, and support the experimental evidence that CO2˙? was formed in its ground vibrational level by the techniques used. The lifetime of CO2˙? calculated with Boltzmann distribution over its vibrational and rotational levels at 298 K, is 1.51 × 10?5 s. There are no direct measurements of the lifetime of N2O˙?, but it was estimated to be greater than 10?4 s from experimental evidence. The predicted lifetimes of N2O˙?, at its lowest vibrational–rotational state (0 K) and lowest vibrational state with rotational levels weighted by the Boltzmann distribution at 298 K, are 238 and 19.1 s, respectively. The lifetime of N2O˙? at thermal equilibrium at 298 K is 6.66 × 10?2 s, indicating that electron loss from the excited vibrational states of N2O˙? is significant. This study represents the first theoretical investigation of CO2˙? and N2O˙? lifetimes. © 1994 John Wiley & Sons, Inc.  相似文献   

13.
Polymerization of MMA was done in the presence of visible light (440 nm) with the use of N-bromosuccinimide (NBS) as the photoinitiator. The initiator exponent and intensity exponent were 0.5, and the monomer exponent was found to be unity. The polymerization was inhibited in the presence of hydroquinone. The average kp2/kt for this photopolymerization system was found to be 0.296 × 10?2 and the activation energy of photopolymerization was 4.67 kcal/mole. Kinetic and other evidence indicate that the overall polymerization takes place by a radical mechanism. With NBS as the photoinitiator, the order of polymerizability at 40°C was MMA, EMA ? MA ? VA, and styrene could not be polymerized under similar conditions.  相似文献   

14.
Vibrationally excited pentyl-1, -2, and -3 radicals were formed selectively by the addition of thermal H atoms to the various pentene isomers with approximately 47 kcal/mole of vibrational energy. Decomposition products other than those expected, along with their pressure dependences, support the fact that either 1,2 or 1,3 hydrogen migrations with either a 3- or 4-member cyclic transition state is occurring with a ka of approximately 3 × 105 or 6 × 105 sec?1. A corresponding critical energy of 33 or 31 kcal/mole is found.  相似文献   

15.
The redox system of potassium persulfate–thiomalic acid (I1–I2) was used to initiate the polymerization of acrylamide (M) in aqueous medium. For 20–30% conversion the rate equation is where Rp is the rate of polymerization. Activation energy is 8.34 kcal deg?1 mole?1 in the investigated range of temperature 25–45°C. Mn is directly proportional to [M] and inversely to [I1]. The range of concentrations for which these observations hold at 35°C and pH 4.2 are [I1] = (1.0–3.0) × 10?3, [I2] = (3.0–7.5) × 10?3, and [M] = 5.0 × 10?2–3.0 × 10?1 mole/liter.  相似文献   

16.
The initiated oxidation of 2, 4-dimethylpentane in the neat liquid phase at 100°C with 760 torr O2 gives more than 90% of a mixture of 2,4-dihydroperoxy-2,4-dimethylpentane and 2-hydroperoxy-2, 4-dimethylpentane in a ratio of 7:1. The rate of oxidation depends closely on the [initiator]1/2, consistent with a mechanism in which chain termination occurs mostly by interactions of two 2-hydroperoxy-2, 4-dimethyl-4-pentylperoxy radicals. 2, 4-Dimethylpentane oxidizes only one sixth as fast as isobutane at the same rate of initiation at 100°C. In cooxidations of the same hydrocarbons, it is 0.71 as reactive as isobutane toward any of the peroxy radicals involved. 2, 4-Dimethylpentane oxidizes 7.5 times as fast at 1.25°C as at 50°C for the same rate of initiation, but the ratio of dihydroperoxide to monohydroperoxide increases only from 5 to 7, corresponding to a difference in activation energy between intramolecular and intermolecular abstraction of 1 kcal/mole. The overall activation energy (EpEt/2) is 10.7 kcal/mole, close to the value of 12 kcal/mole found for isobutane. Absolute values for Ep, Et, kp, kr, and kt were derived. Ring closure of 2-hydroperoxy-2, 4-methyl-4-pentyl radicals to oxetane, not detected during oxidation, was observed when this radical was generated at 100°C in the near-absence of oxygen. The ratio of rate constants for oxetane formation and addition of oxygen to the 2, 4dimethyl-2-hydroperoxy-4-pentyl radical is about 5.4 × 10?5 M at 100°C. Thus, ring closure to oxetane is too slow to compete with addition of oxygen above ?200 torr. At 100°C, 2, 3-dimethylbutane gave no evidence of any intramolecular abstraction. However, 2, 3-dimethylpentane did give at least 12% 2, 4-glycol or hydroxyketone.  相似文献   

17.
Solution polymerization of MMA, with pyridine as the solvent and BZ2O2 and AIBN as thermal initiators, was studied kinetically at 60°C. The monomer exponent varied from 0.45 to 0.91 as [BZ2O2] was increased from 1 × 10?2 to 30 × 10?2 mole/liter in a concentration range of 8.3-4.6 mole/liter for MMA. For AIBN-initiated polymerization the monomer exponent remained constant at 0.69 as [AIBN] varied from 0.4 × 10?2 to 1.0 × 10?2 mole/liter in the same concentration range for MMA. The k2p/kt Value increased in both cases with an increase in pyridine concentration in the system. This was explained in terms of an increase in the kp value, which was due presumably to the increased reactivity of the chain radicals by donor-acceptor interaction between the molecules of solvent pyridine and propagating PMMA radicals and in terms of lowering the kt value for the diffusion-controlled termination reaction due to an increase in the medium viscosity and pyridine content.  相似文献   

18.
The kinetics of the anionic polymerization of octamethylcyclotetrasiloxane (D4) initiated by α-methylstyrene living polymer in tetrahydrofuran was studied. The following kinetic scheme was postulated: Initiation: Propagation: where S- and M represent the initiator and D4, respectively. At a living end concentration of 0.0377 mole/l. and a monomer concentration of 1.5 mole/l. in tetrahydrofuran at 25°C. the following kinetic data were obtained: k1 = 2.3 × 10?4 l./mole-sec., k2 < 2.3 × 10?5 sec.?1, k3 = 2.75 × 10?2l./mole-sec. k4 ≈ 1.17 × 10?2 sec.?1, K1 > 10 l./mole and K2 ≈ 2.35 l./mole. The rate constants k1 and k3 were found to be dependent on the concentration of anions. This is attributed to the dissociation of ion pairs to free ions at lower concentration. Under the experimental conditions studied the majority of the anions were present in the form of ion pairs. The reactivity of the free ions is about 100 times greater than that of ion pairs. There is no temperature effect on K2, indicating zero ΔH and positive ΔS in the propagation reaction.  相似文献   

19.
The I2-catalyzed isomerization of allyl chloride to cis- and trans- l-chloro-l-propene was measured in a static system in the temperature range 225–329°C. Propylene was found as a side product, mainly at the lower temperatures. The rate constant for an abstraction of a hydrogen atom from allyl chloride by an iodine atom was found to obey the equation log [k,/M?1 sec?1] = (10.5 ± 0.2) ?; (18.3 ± 10.4)/θ, where θ is 2.303RT in kcal/mole. Using this activation energy together with 1 ± 1 kcal/mole for the activation energy for the reaction of HI with alkyl radicals gives DH0 (CH2CHCHCl? H) = 88.6 ± 1.1 kcal/mole, and 7.4 ± 1.5 kcal/mole as the stabilization energy (SE) of the chloroallyl radical. Using the results of Abell and Adolf on allyl fluoride and allyl bromide, we conclude DH0 (CH2CHCHF? H) = 88.6 ± 1.1 and DH0 (CH2CHCHBr? H) = 89.4 ± 1.1 kcal/ mole; the SE of the corresponding radicals are 7.4 ± 2.2 and 7.8 ± 1.5 kcal/mole. The bond dissociation energies of the C? H bonds in the allyl halides are similar to that of propene, while the SE values are about 2 kcal/mole less than in the allyl radical, resulting perhaps more from the stabilization of alkyl radicals by α-halogen atoms than from differences in the unsaturated systems.  相似文献   

20.
The rate of oxidation of Ge(II) chloride by large excess of ClO2? ions in HCl, NaCl and Na2SO4 mixed solutions was polarographically observed at various H2O+ and Cl? ion concentrations. The observed rate constant, kobs, is expressed by ko=Kobs/(ClO3?)={k1,(H+)+k2K1(Cl?)2+ K3K2(SO42?)} (H+)/{(H+)1+K1(Cl-)2 +K2(SO42?)} for the following reaction processes, The values were obtained aa k1=1.5410-3liter2 mole2? sec-1, k2=5.00×10-2liter2 mole2? sec-2 and k2=4.30×10-3liter2 mole2? sec-2, K1=1.80× 10-2, K2= 2.43×10-2 mole liter-1 at constant ionic strength I=0.50 M at 30°C.  相似文献   

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