THE Hg 6(3P1) PHOTOSENSITIZED DECOMPOSITION OF CYCLOHEXENE VAPOR

1965 ◽  
Vol 43 (5) ◽  
pp. 1329-1337 ◽  
Author(s):  
G. R. De Maré ◽  
O. P. Strausz ◽  
H. E. Gunning
Keyword(s):  
Triplet State ◽  
Rate Constant ◽  
Bond Cleavage ◽  
Product Distribution ◽  
Ring Closure ◽  
Rate Equations ◽  
Open Chain ◽  
Fragmentation Reactions ◽  
Triplet Biradicals ◽  
Kinetic Features

The reaction follows the pattern established for the triplet state reactions of olefins in general. The major products, ethylene, 1,3-butadiene, vinylcyclobutane, cyclohexane, various C12-compounds, and polymer, can best be accounted for by the allylic C—H and C—C bond cleavage of the primary triplet biradicals and the ring closure and fragmentation reactions of the resulting open chain biradicals. At least three types of triplet state species must be involved in the mechanism. The rate equations, developed on the assumed mechanism, satisfactorily describe the observed product distribution and kinetic features of the system and permit the estimation of the elementary rate constant values and the lifetimes of the various transient biradicals involved. Preliminary experiments with cycloheptene indicate that vinylcyclopentane is an important product.

Kinetische Analyse zur Umwandlung von Oxirenen oder Thiirenen und ihren offenkettigen Valenzisomeren / Kinetic Analysis for the Conversion of Oxirenes or Thiirenes and their Open-Chain Valence Isomers

1980 ◽  
Vol 35 (8) ◽  
pp. 1040-1048 ◽  
Author(s):  
Herbert Meier ◽  
Heinz Kolshorn
Keyword(s):  
Experimental Data ◽  
Kinetic Models ◽  
Ring Opening ◽  
Product Distribution ◽  
Ring Closure ◽  
Quantitative Interpretation ◽  
Open Chain ◽  
Energy Profiles ◽  
Ring Opening Reactions ◽  
Kinetische Analyse

Abstract Ring closure and ring opening reactions possess an outstanding significance for the formation and reactivity of antiaromatic heterocycles like oxirenes and thiirenes. The valence isomerisations 2 ⇆ 1 ⇆ 2' can be controlled by the product distribution 2 → P/2' → P'. A quantitative interpretation of many experimental data, published in the last years, is given on the basis of a few kinetic models, which consider thermal and photochemical pathways. Possible energy profiles of single hypersurfaces (S0 or S1) and the transition between different hypersurfaces (S1 → S0) are the most important features of these models.

Radiolysis of methylcyclopentane. III. Liquid phase mechanism and comparison of cycloalkanes

1968 ◽  
Vol 46 (20) ◽  
pp. 3235-3240 ◽  
Author(s):  
Gordon R. Freeman ◽  
E. Diane Stover
Keyword(s):  
Liquid Phase ◽  
Gas Phase ◽  
Bond Cleavage ◽  
Open Chain ◽  
Methyl Substitution ◽  
Product Yields ◽  
Total Ionization ◽  
Gamma Radiolysis ◽  
G Value

The initial yields of the major products of the gamma radiolysis of liquid methylcyclopentane (MCP) at 25° are: G(H2) = 4.2, G(1-methylcyclopentene plus methylenecyclopentane) = 2.7, G(3- plus 4-methyl-cyclopentene) = 1.0, G(open chain hexene) = 1.0, and G(bimethylcyclopentyl) = 0.9. The effects of scavengers on the product yields are reported and the mechanism is discussed.The liquid phase radiolytic decompositions of cyclohexane (CH), methylcyclohexane (MCH), cyclopentane (CP), and MCP are compared. The net amount of C—C bond cleavage is much greater in the five-membered than in the six-membered rings. Methyl substitution on the ring reduces G(H2) by about one unit, mainly because of the formation of a type of ion (QH+) that does not yield hydrogen when neutralized by an electron. The QH+ type ions are formed in MCH and MCP, but not in CH and CP. In all the systems, another type of ion (N+) that does not yield hydrogen when neutralized by an electron is formed with a G value of about unity. The type of ion (PH+) that does yield hydrogen when neutralized by an electron has a G value of 3.4 in CH and CP, but only 2.0 in MCP. It is concluded that G(total ionization) is in the vicinity of 4.4 in the liquid compounds, virtually the same as the gas phase values.

scholarly journals Kinetics and Thermodynamics Study of Ultrasound-Assisted Depolymerization of k-Carrageenan in Acidic Solution

2020 ◽  
Vol 15 (1) ◽  
pp. 280-289
Author(s):  
Ratnawati Ratnawati ◽  
Nita Indriyani
Keyword(s):  
Molecular Weight ◽  
Rate Constant ◽  
Reaction Rate ◽  
Acidic Solution ◽  
Biomedical Application ◽  
Bond Cleavage ◽  
Reaction Rate Constant ◽  
Order Kinetic ◽  
Kinetics And Thermodynamics ◽  
Ultrasound Assisted

K-carrageenan is a natural polymer with high molecular weight ranging from 100 to 1000 kDa. The oligocarrageenan with low molecular weight is widely used in biomedical application. The aim of this work was to depolymerize k-carrageenan in an acidic solution with the assistance of ultrasound irradiation. The ultrasonication was conducted at various pH (3 and 6), temperatures (30-60 °C), and depolymerization time (0-24 minutes). The results show that the depolymerization reaction follows pseudo-first-order kinetic model with reaction rate constant of 1.856×10-7 to 2.138×10-6 s-1. The reaction rate constant increases at higher temperature and lower pH. The Q10-temperature coefficients of the depolymerization are 1.25 and 1.51 for pH 6 and 3, respectively. The enthalpy of activation (ΔH‡) and the Gibbs energy of activation (ΔG‡) are positive, while the entropy of activation (ΔS‡) is negative, indicating that the activation step of the ultrasound-assisted depolymerization of k-carrageenan is endothermic, non-spontaneous, and the molecules at the transition state is more ordered than at the ground state. The ΔH‡ and the ΔS‡ are not affected by temperature, while the ΔG‡ is a weak function of temperature. The ΔH‡ and ΔS‡ become smaller at higher pH, while the ΔG‡ increases with the increase of pH. The kinetics and thermodynamics analysis show that the ultrasound-assisted depolymerization of k-carrageenan in acidic solution is possibly through three mechanisms, i.e. bond cleavage due to cavitational effect of microbubbles, hydroxyl radical and hydrogen peroxide, as well as proton. Copyright © 2020 BCREC Group. All rights reserved 

scholarly journals Relative Rates of Bond Rotation and Ring Closure in the Photocycloaddition Intermediates from Fullerene-C60 and the Isomeric 2,4-Hexadienes

2019 ◽  
Author(s):  
Wendell Dilling
Keyword(s):  
Relative Rate ◽  
Product Distribution ◽  
Fullerene C60 ◽  
Ring Closure ◽  
Trans Conformation ◽  
Bond Rotation ◽  
Product Distributions

<p>Photocycloaddition of fullerene-C<sub>60 </sub>to the isomeric 2,4-hexadienesreported by Orfanopoulos and co-workers gave a series of 2 + 2 cycloadducts in which bond rotation had occurred in some products. Relative rates of bond rotation and ring closure in the biradical intermediates were calculated from the product distributions using equations developed by Bartlett and co-workers. These data are reinterpreted to show that the ratio of the rate of bond rotation in the intermediate to the rate of ring closure to the cyclobutane product is ~70 for the <i>trans</i>-1-propenyl intermediate formed in the initial cis conformation. Data are inconsistent for the analogous <i>cis</i>-1-propenyl intermediate. The relative rate for the <i>trans</i>-1-propenyl intermediate formed in the initial trans conformation is ~9. Accurate relative rate determinations are highly dependent on very accurate product distribution determinations.</p>

Open-chain nitrogen compounds. Part XV. A kinetic study of the hydrolysis of 1-aryl-3-aryloxymethyl-3-methyltriazenes and related triazenes

1992 ◽  
Vol 70 (8) ◽  
pp. 2224-2233 ◽  
Author(s):  
Keith Vaughan ◽  
Donald L. Hooper ◽  
Marcus P. Merrin
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Buffer System ◽  
Open Chain ◽  
Nucleophilic Displacement ◽  
Ether Oxygen ◽  
Rate Of Hydrolysis ◽  
Electron Withdrawing Group ◽  
Ph Range ◽  
Kinetics Of

The kinetics of hydyrolysis of a series of 1-aryl-3-aryloxymethyl-3-methyltriazenes, Ar-N=N-NMe-CH2OAr′, was studied over the pH range 2–7.5. Reactions were followed by the change in UV absorbance spectra of the triazenes. The aryloxymethyltriazenes decompose more slowly at pH 7.5 than the hydroxymethyltriazenes, Ar-N=NMe-CH2OH; the hydrolysis is favoured by the presence of an electron-withdrawing group in Ar′. A mixed isopropanol/buffer system was developed in order to improve solubility of the aryloxymethyl triazenes. Lowering the pH caused an increase in the rate of hydrolysis and under strongly acidic conditions an electron-withdrawing group in Ar′ actually slows down the reaction. A Hammett plot of the pseudo-first-order rate constant, kobs, is curved, indicating that two or more mechanisms operate simultaneously and that the contribution of each mechanism is substituent-dependent. A plot of kobs vs. [buffer] is linear; the slope of the plot affords the rate constant, kb for the buffer-catalyzed reaction for each substituent. A Hammett plot of kb vs. σ is linear with ρ = +0.55, suggesting that the buffer-catalyzed reaction involves nucleophilic displacement of the phenoxy group by the buffer anion. Further analysis afforded the specific acid-catalyzed rate constants, [Formula: see text], for each substituent; this component of the reaction has a negative ρ, consistent with a mechanism involving protonation at the ether oxygen. The postulation that specific acid catalysis is a component of the reaction mechanism was confirmed by the observation of a solvent deuterium isotope effect, 2.28 > kH/kD > 1.60. Only the p-NO2 and p-CN phenyloxymethyltriazenes showed any spontaneous decomposition.

First determination of the rate constant for ring-closure of an azahexenoyl radical: 6-aza-7-ethyl-5-hexenoyl

2010 ◽  
Vol 46 (35) ◽  
pp. 6521 ◽  
Author(s):  
Sara H. Kyne ◽  
Ching Yeh Lin ◽  
Ilhyong Ryu ◽  
Michelle L. Coote ◽  
Carl H. Schiesser
Keyword(s):  
Rate Constant ◽  
Ring Closure

Synthesis, photophysical characterization, and photoelectrochemical evaluation of a palladium porphyrin sensitizer for TiO2-based dye-sensitized solar cells

2015 ◽  
Vol 19 (09) ◽  
pp. 1021-1031 ◽  
Author(s):  
Seare A. Berhe ◽  
Zachary B. Molinets ◽  
Maya N. Frodeman ◽  
Blair Miller ◽  
Vladimir N. Nesterov ◽  
...  
Keyword(s):  
Solar Cells ◽  
Triplet State ◽  
High Efficiency ◽  
Dye Sensitized Solar Cells ◽  
Product Distribution ◽  
Dye Sensitized ◽  
Meso Position ◽  
Photophysical Behavior ◽  
Sensitized Solar Cells ◽  
Excited State Quenching

An unsymmetrical (A3B) palladium porphyrin bearing a cyanoacrylic acid at one meso position has been synthesized for evaluation as a photosensitizer in dye-sensitized solar cells based on titanium dioxide ( TiO 2) as a comparison to other metalloporphyrins and as a proxy for other potential triplet-state photosensitizer compounds. The synthesis of this palladium porphyrin has provided new insight into the mechanism and product distribution of decarboxylative hydrolysis of malonic acid when attached at the porphyrin meso position. A crystal structure determination for a meso-formyl palladium porphyrin has been determined, showing saddle-distortion of the porphyrin core. The photophysical behavior of the palladium porphyrin sensitizer and its performance in photoelectrochemical cells are described and interpreted in the context of bimolecular excited state quenching pathways including oxygen sensitization, triplet–triplet annihilation and electron transfer events. Palladium porphyrins are proposed as a sensitizer class with potential for high efficiency dye-sensitized solar cells, but with the caveat that some overpotential for electron injection is necessary to compete against the multiple decay pathways that are specially available to triplet state photosensitizers.

Detection and chemistry of the triplet state of thymine

1970 ◽  
Vol 48 (4) ◽  
pp. 694-696 ◽  
Author(s):  
A. G. Szabo ◽  
W. D. Rlddell ◽  
R. W. Yip
Keyword(s):  
Excited State ◽  
Triplet State ◽  
Rate Constant ◽  
Triplet Excited State

The transient produced on flash excitation of degassed solutions of thymine in acetonitrile has been characterized as the triplet excited state of thymine. This triplet state has a lifetime of 14 ± 1 μs and the associated dimerization rate was found to be 5.3 ± 0.3 × 108 M−1 s−1. The triplet state of thymine could be quenched by 2,4-hexadien-1-ol with a rate constant of 8.1 ± 0.6 × 109 M−1 s−1.

Phenyl Substitution Effects on Triplet–Triplet Absorption Spectra: I. Study of 1,3,6,8-Tetraphenylpyrene

1975 ◽  
Vol 53 (21) ◽  
pp. 3269-3275 ◽  
Author(s):  
C. Rullière ◽  
E. C. Colson ◽  
P. C. Roberge
Keyword(s):  
Absorption Spectrum ◽  
Triplet State ◽  
Absorption Spectra ◽  
Rate Constant ◽  
Theoretical Calculations ◽  
Vibrational Structure ◽  
Substitution Effects ◽  
Quenching Rate ◽  
Diffusion Controlled ◽  
Quenching Rate Constant

The triplet–triplet (T–T) absorption spectrum of 1,3,6,8-tetraphenylpyrene (TPP) was measured from 400 to 620 nm. The data obtained are compared with theoretical calculations using the Ruedenberg–Scherr FEMO model. A planar triplet state is evidenced by fine vibrational structure. The T–T quenching rate constant measured (1.3 ± 0.1 × 109 M−1 s−1) is 20% of the expected diffusion-controlled value.

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