- The rate of excited-state proton transfer to solvent from trifluoromethylphenols in water
-
The proton-transfer reactions to solvent from electronically excited o-, m-, and p-(trifluoromethyl)phenols (TFOHs) in water have been investigated by picosecond time-resolved fluorescence measurements. The rate constants for the proton dissociation of o-, m-, and p-TFOH are obtained to be 2.2 × 10 9, 8.6 × 108, and 2.5 × 108 s -1, respectively. On the basis of the rate constants, the effects of substituent and deuterium isotope effects on the proton-transfer reactions are revealed. copyright
- Kaneko, Shigeo,Yoshihara, Toshitada,Tobita, Seiji
-
-
Read Online
- Alkali and alkaline-earth metal ion catalysis in the reaction of aryl acetates with methoxide ion. Effect of a poly(oxyethylene) side arm
-
The effect of added alkali (Na, K) and alkaline-earth (Sr, Ba) metal bromides on the rate of acyl transfer from o-acetoxyphenyl 3,6,9,12-tetraoxatridecyl ether (2) to methoxide ion in methanol at 25 °C has been investigated spectrophotometrically. All of the added salts increased significantly the rate of reaction in the order Na+ + 2+ 2+, a maximum catalytic effect of nearly 102 being observed with the latter metal ion. A proper analysis of rate data afforded equilibrium constants for associations of metal ions with reactants and transition state, showing that in all cases the transition state binds metal ions much more strongly than the reactants. An analogous set of rate measurements was carried out for comparison purposes on the corresponding reaction of phenyl acetate (1). The fact that catalytic effects are much greater with 2 than with 1 reveals that a substantial contribution to the stability of the transition state of the metal ion assisted path arises from interaction of the metal ion with the oxygen donors of the side arm.
- Ercolani,Mandolini
-
-
Read Online
- Kinetics and Mechanism of the Aminolysis of Phenyl Thionoacetate in Aqueous Solution
-
The reactions of a series of secondary alicyclic amines with the title substrate have been subjected to a kinetic study in water at 25 deg C, ionic strength 0.2 M.Pseudo-first-order rate coefficients (kobsd) are found throughout, under amine ex
- Castro, Enrique A.,Ibanez, Fernando,Santos, Jose G.,Ureta, Carmen
-
-
Read Online
- CATALYSIS BY ALKALI AND ALKALINE-EARTH METAL IONS IN NUCLEOPHILIC ATTACK OF METHOXIDE ION ON CROWN ETHERS BEARING AN INTRA-ANNULAR ACETOXY GROUP
-
Rates of reaction of methoxide ion with crown ethers bearing an intra-annular acetoxy group are markedly enhanced by alkali and alkali-earth metal bromides as a result of much stronger interactions of the metal ions with transition states than with reactants.
- Cacciapaglia, Roberta,Lucente, Silvia,Mandolini, Luigi,van Doorn, Arie R.,Reinhoudt, David N.,et al
-
-
Read Online
- NEW INSIGHT INTO THE MECHANISMS OF REACTIONS BETWEEN SOME ANIONIC NUCLEOPHILES AND PHENYL ACETATE IN THE GAS PHASE
-
Experiments carried out in an ion cyclotron resonance (ICR) drift cell, an ICR trapped ion cell and a flowing afterglow (FA) system show that in the gas phase phenyl acetate reacts with a variety of clustered and unclustered nucleophiles to yield mainly the product ion C6H5O-.
- Kleingeld, Jan C.,Nibbering, Nico M.M.,Grabowski, Joseph J.,DePuy, Charles H.,Fukuda, Elaine K.,McIver, Robert T.
-
-
Read Online
- Gas-phase proton-transfer reactions between alkoxide anions
-
Reaction efficiencies for proton transfer between alkoxide anions and neutral alcohols have been measured in an ion cyclotron resonance spectrometer, using a competition kinetics technique. The efficiencies for identity proton-transfer reactions are measurably less than 0.5, which is the simple statistical prediction for a thermoneutral reaction with no energetic barrier. In addition, the trend in reaction efficiencies for exothermic proton transfers is consistent with the presence of a substantial Marcus intrinsic barrier. An energetic barrier of this magnitude is not consistent with a surface which is believed to have little or no barrier. The results are consistent, however, with recent quasi-classical trajectory calculations which show that efficiencies for reactions on a barrierless surface can be slower than expected.
- Dodd, James A.,Baer, Susan,Moylan, Christopher R.,Brauman, John I.
-
-
Read Online
- Kinetic Study on Nucleophilic Substitution Reactions of O-Phenyl O-Y-substituted-Phenyl Thionocarbonates with 1,8-Diazabicyclo[5.4.0]undec-7-ene in Acetonitrile
-
Second-order rate constants (kN) for nucleophilic substitution reactions of O-phenyl O-Y-substituted-phenyl thionocarbonates (4a–4k) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in MeCN at 25.0 ± 0.1°C are reported. The reactivity of 4a–4k decreases as basicity of the leaving group increases except O-2,4-dinitrophenyl O-phenyl thionocarbonate (4a), which is less reactive than O-3,4-dinitrophenyl O-phenyl thionocarbonate (4b) although the former possesses 2 pKa units less basic nucleofuge than the latter. The Br?nsted-type plot for the reactions of 4b–4k is linear with βlg = ?0.50, a typical βlg value for reactions reported to proceed through a concerted mechanism. The Hammett plot correlated with σY? constants for the reactions of 4b–4k results in a better linear correlation than that correlated with σYo constants. Besides, the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρY = 2.12, r = 0.68 and R2 = 0.990, indicating that a negative charge develops partially on the O atom of the leaving group in the rate-determining step (RDS). Thus, the reactions have been concluded to proceed through a forced concerted mechanism. Effects of steric hindrance on reactivity and reaction mechanism are also discussed in detail.
- Um, Ik-Hwan,Park, Kyoung-Ho
-
p. 1169 - 1173
(2017/09/13)
-
- Kinetic study on alkaline hydrolysis of Y-substituted phenyl picolinates: Effects of modification of nonleaving group from benzoyl to picolinyl on reactivity and reaction mechanism
-
Second-order rate constants (kOH-) for alkaline hydrolysis of Y-substituted phenyl picolinates (6a-6i) have been measured spectrophotometrically. A linear Bronsted-type plot is obtained with βlg = -0.34, which is typical for reactions reported previously to proceed through a stepwise mechanism with formation of an addition intermediate being the rate-determining step (RDS). However, σYo constants result in a much poorer Hammett correlation than σY- constants. Furthermore, the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρY = 0.82 and r = 0.72, indicating that a negative charge develops partially on the O atom of the leaving group in the RDS. Thus, the reactions have been concluded to proceed through a forced concerted mechanism with a highly unstable intermediate 7. Comparison of the current kinetic data with those reported previously for the corresponding reactions of Y-substituted phenyl benzoates has revealed that modification of the nonleaving group from benzoyl to picolinyl causes not only an increase in reactivity but also a change in the reaction mechanism (i.e., from a stepwise mechanism to a forced concerted pathway).
- Kim, Myung-Joo,Kim, Min-Young,Um, Ik-Hwan
-
p. 1138 - 1142
(2015/07/15)
-
- Alkaline hydrolysis of Y-substituted phenyl phenyl thionocarbonates: Effect of changing electrophilic center from C=O to C=S on reactivity and mechanism
-
Second-order rate constants (kOH-) have been measured spectrophotometrically for reactions of Y-substituted phenyl phenyl thionocarbonates (4a-i) with OH- in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The ksu
- Kim, Song-I,Park, Hey-Ran,Um, Ik-Hwan
-
scheme or table
p. 179 - 182
(2011/10/31)
-
- Study on the transesterification of methyl aryl phosphorothioates in methanol promoted by Cd(II), Mn(II), and a synthetic Pd(II) complex
-
Methanol solutions containing Cd(II), Mn(II), and a palladacycle, (dimethanol bis(N,N-dimethylbenzylamine-2C,N)palladium(II) (3), are shown to promote the methanolytic transesterification of O-methyl O-4-nitrophenyl phosphorothioate (2b) at 25 °C with impressive rate accelerations of 10 6-1011 over the background methoxide promoted reaction. A detailed mechanistic investigation of the methanolytic cleavage of 2a-d having various leaving group aryl substitutions, and particularly the 4-nitrophenyl derivative (2b), catalyzed by Pd-complex 3 is presented. Plots of k obs versus palladacycle [3] demonstrate strong saturation binding to form 2b:3. Numerical fits of the kinetic data to a universal binding equation provide binding constants, Kb, and first order catalytic rate constants for the methanolysis reaction of the 2b:3 complex (kcat) which, when corrected for buffer effects, give corrected (kcat corr) rate constants. A sigmoidal shaped plot of log(k catcorr) versus sspH (in methanol) for the cleavage of 2b displays a broad sspH independent region from 5.6 ≥ sspH ≥ ~10 with a k minimum = (1.45 ± 0.24) × 10-2 s-1 and a [lyoxide] dependent wing plateauing above a kinetically determined sspKa of 12.71 ± 0.17 to give a k maximum = 7.1 ± 1.7 s-1. Bronsted plots were constructed for reaction of 2a-d at sspH 8.7 and 14.1, corresponding to reaction in the midpoints of the low and high s spH plateaus. The Bronsted coefficients (βLG) are computed as -0.01 ± 0.03 and -0.86 ± 0.004 at low and high sspH, respectively. In the low sspH plateau, and under conditions of saturating 3, a solvent deuterium kinetic isotope effect of kH/kD = 1.17 ± 0.08 is observed; activation parameters (ΔHPd? = 14.0 ± 0.6 kcal/mol and ΔSPd?= -20 ± 2 cal/mol?K) were obtained for the 3-catalyzed cleavage reaction of 2b. Possible mechanisms are discussed for the reactions catalyzed by 3 at low and high sspH. This catalytic system is shown to promote the methanolytic cleavage of O,O-dimethyl phosphorothioate in CD3OD, producing (CD3O)2P=O(S-) with a half time for reaction of 34 min.
- Edwards, David R.,Neverov, Alexei A.,Brown, R. Stan
-
scheme or table
p. 1786 - 1797
(2011/04/23)
-
- Structure and mechanism of PhnP, a phosphodiesterase of the carbon-phosphorus lyase pathway
-
PhnP is a phosphodiesterase that plays an important role within the bacterial carbon-phosphorus lyase (CP-lyase) pathway by recycling a "dead-end" intermediate, 5-phospho-α-d-ribosyl 1,2-cyclic phosphate, that is formed during organophosphonate catabolism
- He, Shu-Mei,Wathier, Matthew,Podzelinska, Kateryna,Wong, Matthew,McSorley, Fern R.,Asfaw, Alemayehu,Hove-Jensen, Bjarne,Jia, Zongchao,Zechel, David L.
-
experimental part
p. 8603 - 8615
(2012/07/27)
-
- Analysis of linear free-energy relationships combined with activation parameters assigns a concerted mechanism to alkaline hydrolysis of X-substituted phenyl diphenylphosphinates
-
A kinetic study is reported for alkaline hydrolysis of X-substituted phenyl diphenylphosphinates (1a-i). The Bronsted-type plot for the reactions of 1a-i is linear over 4.5 pKa units with βlg= -0.49, a typical βlg value for reactions which proceed through a concerted mechanism. The Hammett plots correlated with σo and σ- constants are linear but exhibit many scattered points, while the corresponding Yukawa-Tsuno plot results in excellent linear correlation with ρ= 1.42 and r=0.35. The r value of 0.35 implies that leaving-group departure is partially advanced at the rate-determining step (RDS). A stepwise mechanism, in which departure of the leaving group from an addition intermediate occurs in the RDS, is excluded since the incoming HO - ion is much more basic and a poorer nucleofuge than the leaving aryloxide. A dissociative (DN + AN) mechanism is also ruled out on the basis of the small βlg value. As the substituent X in the leaving group changes from H to 4-NO2 and 3,4-(NO2)2, ΔH≠ decreases from 11.3 kcal mol-1 to 9.7 and 8.7 kcal mol-1, respectively, while ΔS≠ varies from -22.6 cal mol-1 K-1 to -21.4 and -20.2 cal mol-1 K-1, respectively. Analysis of LFERs combined with the activation parameters assigns a concerted mechanism to the current alkaline hydrolysis of 1a-i.
- Um, Ik-Hwan,Han, Jeong-Yoon,Hwang, So-Jeong
-
supporting information; experimental part
p. 7324 - 7330
(2009/08/07)
-
- Reactions of [aryloxy(phenyl)carbene]pentacarbonylchromium(0) complexes with thiolate ions. Decreasing reactivity with increasing basicity of the nucleophile
-
(Chemical Equation Presented) A kinetic study of the reactions of thiolate ions with three Fischer-type [aryloxy(phenyl)carbene]-pentacarbonyl chromium(0) complexes in 50% MeCN-50% water (v/v) is reported. Bronsted plots of the second-order rate constants are biphasic with an initial steep rise for weakly basic thiolate ions (βnuc ≈ 1.0) followed by a slightly descending leg with a negative slope (βnuc ≈ -0.2) for strongly basic thiolate ions. This indicates a change from rate-limiting leaving group departure at low pKaRSH to rate-limiting nucleophilic attachment at high pKaRSH. The negative βnuc values result from a combination of minimal progress of C-S bond formation at the transition state and the requirement for partial desolvation of the nucleophile before it enters the transition state. Possible factors that may affect the degree of bond formation in reactions of Fischer carbene complexes as well as reactions of other unsaturated electrophiles with thiolate ions are discussed.
- Bernasconi, Claude F.,Perez-Lorenzo, Moises,Codding, Sara J.
-
p. 9456 - 9463
(2008/03/15)
-
- Alkaline phosphatase mono- and diesterase reactions: Comparative transition state analysis
-
Enzyme-catalyzed phosphoryl transfer reactions have frequently been suggested to proceed through transition states that are altered from their solution counterparts. Previous work with Escherichia coli alkaline phosphatase (AP), however, suggests that thi
- Zalatan, Jesse G.,Herschlag, Daniel
-
p. 1293 - 1303
(2007/10/03)
-
- Mechanistic change in the reactivity of substituted phenyl acetates over phenyl thiolacetates toward imidazole in aqueous phase
-
The kinetics of aminolysis of several substituted phenyl acetates by imidazole is studied in aqueous medium at 20°C and an ionic strength of 0.1 M (KCl). By following the leaving groups spectrophotometrically (λ max = 272-401 nm), under excess free imidazole, pseudo-first-order rate constants (κobs) are obtained. For the esters with good nucleofuges, the reaction follows clean second-order kinetics and the plots of (κobs - κH) against free imidazole concentration are linear at constant pH. The macroscopic nucleophilic substitution rate constants (κN) are obtained as the slopes of these plots and found to be pH independent. For the esters with poor nucleofuges, a rate dependence on more than first power of the free imidazole and a linear dependence of κ′2 on free imidazole is observed. Accordingly, the microscopic rate constants for the assisted paths viz. κga and κgb have been disseminated besides for simple bimolecular attack. The Broensted-type plots and Hammett plots were constructed whose slope values are consistent with a stepwise mechanism through a bipolar tetrahedral addition intermediate whose formation or breakdown being rate determining for various paths. Comparison of this reaction of oxyesters with the earlier reported works on similar reaction of analogue thiolesters under identical reaction conditions showed remarkable mechanistic differences which are discussed in detail. The discussion is extended to include the details on previously studied ammonolysis of these two types of esters wherein thiolesters showed differed reactivity than that reported in the present study.
- Rajarathnam,Jeyakumar,Nadar, P. Ananthakrishna
-
p. 211 - 221
(2007/10/03)
-
- Kinetics and mechanistic study of the reaction of cyclic anhydrides with substituted phenols. Structure-reactivity relationships
-
(Chemical Equation Presented) The kinetic of the reactions of phthalic and maleic anhydrides with different substituted phenols (Z-PhOH with Z = H, m-CH3, p-CH3, m-Cl, p-Cl, and m-CN) were studied in aqueous solution. Two kinetic processes well separated in time were observed. The fast one is attributed to the formation of the aryl ester in equilibrium with the anhydride and allows the determination of the rate of nucleophilic attack of the phenol on the anhydride (k-A). From the slow kinetic process, the equilibrium constant for this reaction was determined. The Broensted-type plots for the nucleophilic attack of substituted phenols on the anhydrides were linear with slopes βNuc of 0.45 and 0.56 for phthalic and maleic anhydride, respectively. The results are consistent with a mechanism involving rate-determining nucleophilic attack and also with a concerted mechanism. The calculated effective charge on the atoms involved in the reactions and the Broensted β values are consistent with a mechanism involving a concerted or enforced concerted mechanism where a tetrahedral intermediate with significant lifetime is not formed along the reaction coordinate. The latter mechanism is preferred over the stepwise process.
- Andres, Gabriel O.,De Rossi, Rita H.
-
p. 1445 - 1449
(2007/10/03)
-
- Curved Hammett Plot in Alkaline Hydrolysis of O-Aryl Thionobenzoates: Change in Rate-Determining Step versus Ground-State Stabilization
-
Second-order rate constants have been measured for alkaline hydrolysis of O-aryl thionobenzoates (X-C6H4-CS-OC6H 4-Y) in 80 mol % H2O-20 mol % DMSO at 25.0 ± 0.1 °C. The Hammett plot for the reaction of O-4-nitrophenyl X-substituted thionobenzoates (X-C6H4-CS-OC6H 4-NO2, 1a-e) exhibits a downward curvature. However, a possible traditional explanation in terms of a change in the rate-determining step (RDS) has been considered but rejected. The proposed explanation involves stabilization of the ground-state (GS) through-resonance interaction between the electron-donating substituent X and the thionocarbonyl functionality on the basis of the linear Yukawa-Tsuno plot obtained for the same reaction. The Bronsted-type plot for the reaction of O-aryl thionobenzoates (C 6H5-CS-OC6H4-Y, 2a-i) is linear but exhibits many scattered points with a small βlg, (-0.35). The Hammett plot for the same reaction shows rather poor correlation with σ- constants but much better correlation with σ° constants. The alkaline hydrolysis of O-aryl thionobenzoates (1a-e and 2a-i) has been proposed to proceed through an addition intermediate in which bond formation is the RDS.
- Um, Ik-Hwan,Lee, Ji-Youn,Kim, Han-Tae,Bae, Sun-Kun
-
p. 2436 - 2441
(2007/10/03)
-
- Mechanistic information from pressure acceleration of hydride formation via proton binding to a cobalt(I) macrocycle
-
The effect of pressure on proton binding to the racemic isomer of the cobalt(I) macrocycle, CoL+ (L = 5,7,7,12.-14, 14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene), has been studied for a series of proton donors using pulse radiolysis techniques. The second-order rate constants for the reaction of CoL+ with proton donors decrease with increasing pKa of the donor acid, consistent with a reaction occurring via proton transfer. Whereas the corresponding volumes of activation (ΔV?) are rather small and negative for all acids (proton donors) with pKa values below 8.5, significantly larger negative activation volumes are found for weaker acids (pKa> 9.5) containing OH groups as proton donors. In the latter case, the observed ΔV? for these protonation reactions show a correlation with the reaction volumes (ΔV°ion) for the ionization of the weak acids with a slope of 0.44, indicating that bond dissociation of the weak acid molecule bound to the metal center proceeds approximately halfway at the transition state along the reaction coordinate in terms of volume changes.
- Fujita, Etsuko,Wishart, James F.,Van Eldik, Rudi
-
p. 1579 - 1583
(2008/10/08)
-
- Reinterpretation of curved hammett plots in reaction of nucleophiles with aryl benzoates: Change in rate-determining step or mechanism versus ground-state stabilization
-
A kinetic study is reported for the reaction of the anionic nucleophiles OH-, CN-, and N3- with aryl benzoates containing substituents on the benzoyl as well as the aryloxy moiety, in 80 mol % H2O-20 mol % dimethyl sulfoxide at 25.0 °C. Hammett log k vs σ plots for these systems are consistently nonlinear. However, a possible traditional explanation in terms of a mechanism involving a tetrahedral intermediate with curvature resulting from a change in rate-determining step is considered but rejected. The proposed explanation involves ground-state stabilization through resonance interaction between the benzoyl substituent and the electrophilic carbonyl center in the two-stage mechanism. Accordingly, the data are nicely accommodated on the basis of the Yukawa-Tsuno equation, which gives linear plots for all three nuceophiles. Literature reports of the mechanism of acyl transfer processes are reconsidered in this light.
- Um, Ik-Hwan,Han, Hyun-Joo,Ahn, Jung-Ae,Kang, Swan,Buncel, Erwin
-
p. 8475 - 8480
(2007/10/03)
-
- Kinetics and mechanism of phosphate-catalyzed hydrolysis of benzoate esters: Comparison with nucleophilic catalysis by imidazole and o-iodosobenzoate
-
Phosphate-catalyzed hydrolysis of 2,4-dinitrophenyl 4-X-benzoate, and 3- or 4-Y-phenyl 3,5-dinitrobenzoates, where X and Y are substituents, has been studied spectrophotometrically. The following conclusions are based on catalytic rate constants, solvent
- El Seoud, Omar A.,Ruasse, Marie-Francoise,Rodrigues, Wagner A.
-
p. 1053 - 1058
(2007/10/03)
-
- The influence of the structure of tetracoordinate phosphorus acid esters on the catalytic effect of the sodium dodecyl sulfate - hexanol - water ternary reverse micellar system
-
The catalytic effect of the sodium dodecyl sulfate - hexanol - water ternary reverse micellar system in the alkaline hydrolysis of O-alkyl O′-aryl chloromethylphosphonates as a function of the substrate structure was studied. The micellar effect is mainly determined by a change in the electronic properties of the substituents, while the hydrophobicity plays a secondary role. The kinetic data were examined in the framework of the pseudo-phase model of micellar catalysis. The rate constants of the reaction in the surface layer and the partition constants of the reactants were calculated.
- Zakharova,Valeeva,Shagidullina,Kudryavtseva
-
p. 1360 - 1364
(2007/10/03)
-
- The micellar effect of the sodium bis(2-ethylhexyl)sulfosuccinate - decane - water reverse system on the hydrolysis of phosphoric acid esters
-
The reactivity of alkyl aryl chloromethylphosphonates in alkaline hydrolysis in the sodium bis(2-ethylhexyl)sulfosuccinate - decane - water reverse micellar system is mainly determined by the electronic properties of substituents and depends only slightly on their hydrophobicity.
- Zakharova,Valeeva,Shagidullina,Kudryavtseva
-
p. 1696 - 1698
(2007/10/03)
-
- The mechanism of the metal ion promoted cleavage of RNa phosphodiester bonds involves a general acid catalysis by the metal aquo ion on the departure of the leaving group
-
A series of uridine 3′-alkyl phosphates and 3′-aryl phosphates were synthesised and their cleavage was studied in the presence of Zn2+ aquo ions. A βlg value was determined for the Zn2+ promoted cleavage of both types of compounds. Comparison of the results obtained to those reported previously for the cleavage of the same substrates in the absence of metal ion catalysts suggests that the alkyl leaving group departs as an alcohol in the presence of metal ion catalysts. Furthermore, metal ion catalysts seem to enhance the departure. The aryl leaving group, in contrast, departs as an oxyanion.
- Mikkola, Satu,Stenman, Eeva,Nurmi, Kirsi,Yousefi-Salakdeh, Esmail,Stroemberg, Roger,Loennberg, Harri
-
p. 1619 - 1625
(2007/10/03)
-
- Electrochemistry of electron transfer probes. α-aryloxyacetoveratrones and implications for the mechanism of photo-yellowing of pulp1
-
Standard potentials (Eo) of a series of substituted α-aryloxyacetoveratrone derivatives have been determined from a correlation of the 13C NMR chemical shifts of the carbonyl group and a similar correlation (Eo vs. 13C NMR shifts) within a series of α-anilinoacetoveratrones. Using these potentials the rate constants for fragmentation of the radical anions were determined by digital simulation of the voltammetric waves. The rate contants for C O cleavage in the radical anions correlate with the pKa of the corresponding phenols. The fragmentations are all in the activated region of a general free energy relationship for this class of compound (α = 0.5). The standard potential and rate constant for fragmention of the α-guaiacoxyacetoveratrone radical anion also were determined. This species is a model compound for one of the lignin substructures. The implication of these results on the currently accepted mechanism for photo-yellowing of lignin rich paper is discussed.
- Andersen, Mogens L.,Wayner, Danial D. M.
-
p. 830 - 836
(2007/10/03)
-
- Reactivity of phosphate diesters doubly coordinated to a dinuclear Cobalt(III) complex: Dependence of the reactivity on the basicity of the leaving group
-
Reactivities of eight phosphate diesters each coordinated to a dinuclear Co(III) complex were investigated ([Co2(tacn)2(OH)2{O2P(OR)2}]3+; tacn = 1,4,7-triazacyclononane). Four of the complexes were coordinated by substituted phenyl methyl phosphates (substituent m-F, p-NO2 (1a); p-NO2 (1b); m-NO2 (1c); unsubstituted (1d)) and two by substituted phenyl 2- hydroxypropyl phosphates (substituent p-NO2 (2a); unsubstituted (2b)). Reactivities of dialkyl phosphates coordinated to the dinuclear Co(III) complex (1,2-propylene phosphate (3); dimethyl phosphate (4)) were also investigated. Hydrolysis of the phosphate diesters in 1a to 1d takes place by intramolecular oxide attack on the bridging phosphate while hydrolysis of 3 principally takes place by intermolecular hydroxide attack on the bridging phosphate. The diester in 2a cleaves by intramolecular oxide attack while that in 2b cleaves by intramolecular transesterification. Dimethyl phosphate dissociates from 4 without any observable cleavage of the diester. These results can be understood in terms of the More O'Ferrall-Jencks energy diagram, and they indicate that there will be considerable cooperativity between the oxide activation and leaving group activation.
- Williams, Nicholas H.,Cheung, William,Chin, Jik
-
p. 8079 - 8087
(2007/10/03)
-
- Internal excitation in the products of nucleophilic substitution from the dissociation of metastable ion complexes
-
The relative kinetic energy distributions for the products of the dissociation of four metastable gasphase ion clusters have been analyzed by means of ion kinetic energy spectroscopy, and the results modeled using statistical phase space theory. The systems studied represent reaction intermediates in bimolecular nucleophilic substitutions (S(N)2). These studies build on previous investigations that demonstrated vibrational excitation in the products of the substitution reactions of halide ions with methyl halides. The present studies explore the effects of molecular structure, reaction exothermicity, and nucleophile and leaving group variation. The experimental kinetic energy distributions are compared with theoretical distributions calculated for statistical partitioning of energy among internal modes and relative kinetic energy of the products. In each reaction, the calculated distributions agree with the experimental distributions only if a significant fraction of the energy released in the exothermic reactions is assumed to be unavailable for randomization in the dissociation. The results suggest that the products of these S(N)2 reactions are internally excited.
- Graul, Susan T.,Carpenter, Catherine J.,Bushnell, John E.,Van Koppen, Petra A. M.,Bowers, Michael T.
-
p. 6785 - 6796
(2007/10/03)
-
- Acid dissociation constants of phenols and reaction mechanism for the reactions of substituted phenyl benzoates with phenoxide anions in absolute ethanol
-
Acid dissociation constants of 10 substituted phenols have been measured by a kinetic method together with second-order rate constants for the reactions of aryl benzoates (X-C6H4CO-OC6H4-Y) with Z-substituted phenoxide (Z-C6H4O-) and EtO- in absolute ethanol at 25.0 ± 0.1°C. The kinetic results support a stepwise mechanism for the present acyl-transfer reaction.
- Um, Ik-Hwan,Hong, Yeon-Ju,Kwon, Dong-Sook
-
p. 5073 - 5082
(2007/10/03)
-
- Electrochemistry of electron-transfer probes. The role of the leaving group in the cleavage of radical anions of α-aryloxyacetophenones
-
The formal reduction potential (E°) of α-phenoxyacetophenone has been determined from the voltammetric peak potential obtained by linear sweep voltammetry in combination with the rate constant for fragmentation of the radical anion which had been determin
- Andersen, Mogens L.,Mathivanan,Wayner, Danial D. M.
-
p. 4871 - 4879
(2007/10/03)
-
- Reduction potentials and kinetics of electron transfer reactions of phenylthiyl radicals: Comparisons with phenoxyl radicals
-
The reduction potentials relative to the standard hydrogen electrode (SHE) for a number of para-substituted phenylthiyl radicals (Eo(p-XC6H4S./p-XC6H 4S-)) have been derived from pulse radiolytic studies of electron transfer equilibria which compare their values to those of radicals of known reduction potentials. A ladder combining the reduction potentials for both phenylthiyl and phenoxyl radicals has been established. These reduction potentials have been shown to be self-consistent and are intermediate between those of p-benzosemiquinone radical anion at 0.02 V and phenoxyl radical at 0.79 V. The reduction potential decreases as the electron donating power of the para substituent rises. The substituent effect is, however, much weaker for the phenylthiyl radicals than for their oxygen analogs. These observations demonstrate that the electronic interaction between the sulfur atoms and the aromatic ring system is much less than that which occurs with oxygen atoms. Examination of the rates of electron transfer in terms of the Marcus theory indicates that the reorganization energies of both p-XC6H4O. and p-XC6H4S. radicals are similarly affected by H, CH3, and CH3O substitution. However, the reorganization energies increase substantially for H2N and O- para substituents with the effect being much less for the p-XC6H4S. radicals than for the p-XC6H4O. radicals. These observations are in accord with structural information from spectroscopic and theoretical studies of the radicals which show that in the latter system the substituent groups interact strongly with the aromatic π system.
- Armstrong,Sun, Qun,Schuler
-
p. 9892 - 9899
(2007/10/03)
-
- Electron transfer as a possible initial step in nucleophilic addition elimination reactions between (radical) anions and carbonyl compounds in the gas phase
-
The reactions of the HO-, CH3S-, CH2S- and CH2=C(CH3)-CH2- ions with three ketones (CF3COR; R=CH3, CF3, C6H5) and three esters of trifluoroacetic acid (CF3CO2R; R=CH3, C2H5 and C6H5) have been studied with use of Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry. All four negative ions react exclusively by proton transfer with CF3COCH3. With the other substrates, the HO- ion reacts by various pathways, such as proton transfer, SN2 substitution, E2 elimination and attack on the carbonyl group. The CH3S- ion is unreactive towards CF3COC6H5 but is able to react by hydride transfer, SN2, E2 and/or carbonyl attack with the remaining neutral species. The CH2S- radical anion reacts by electron transfer to afford stable molecular radical anions of CF3COCF3 and CF3COC6H5, whereas the main reaction with the two esters, CF3CO2CH3 and CF3CO2C2H5, is dissociative electron transfer leading to CF3CO2- and CF3- ions. The CH2=C(CH3)-CH2- anion displays a more complex reactivity pattern involving electron transfer, SN2, E2 as well as attack on the carbonyl group. Direct evidence for the occurrence of electron transfer as the initial step in an overall BAC2 type process has not been obtained for the systems studied. The reaction of the CH2S- ion with CF3CO2C6H5 was observed, however, to yield exclusively a CF3COCHS-. radical anion. Based upon the absence of a BAC2 process in the reaction of CH2S- with the methyl and ethyl esters of trifluoroacetic acid in combination with the facile occurrence of electron transfer from this radical anion, it is suggested that the CF3COCHS-. ion is formed by an initial electron transfer followed by coupling between the CH2S molecule and the CF3CO2C6H5- radical anion and subsequent loss of C6H5OH from the collision complex.
- Staneke, Paul O.,Ingemann, Steen,Nibbering, Nico M. M.
-
p. 179 - 184
(2007/10/03)
-
- Effect of Cationic Micelles on the intramolecular General Base-catalysed Hydrolysis of Ionized Phenyl Salicylate at Different Temperatures
-
An increase in the total concentration of cetyltrimethylammonium bromide (CTABr), from 0.0 to 0.12 mol dm-3 causes the pseudo-first-order rate constant for intramolecular general base-catalysed hydrolysis of ionized phenyl salicylate (PS-) to decrease by nearly five- or six-fold at constant temperature, while an increase in temperature from 30 to 58 deg C increases the first-order rate constant from 7.10*10-5 to 123*10-5 s-1 as well as decreasing the PS--micelle binding constants from 7100 to nearly 5000 dm3 mol-1.
- Khan, Mohammad Niyaz,Arifin, Zainudin
-
p. 132 - 133
(2007/10/03)
-
- Gas-Phase Nucleophilic Displacement Reactions
-
Displacement reactions of each of a variety of anionic nucleophiles reacting with each of a variety of neutrals have been studied by pulsed ion cyclotron resonance (ICR) spectroscopy.Rate constants for these reactions are interpreted in terms of a three-step reaction sequence.RRKM calculations are used to obtain information about the energy of transition states.The origin of the barrier to reaction in solution is discussed.
- Olmstead, William N.,Brauman, John I.
-
p. 1653 - 1662
(2007/10/03)
-
- Hammett Equation and Micellar Effects upon Deacylation
-
Substituent effects upon second order rate constants of reaction of OH- with phenyl p-substituted benzoates at surface of micelles of cetyltrialkylammonium bromide (alkyl = Me, Et, Pr and Bu) and tetradecylquinuclidinium bromide fit the Hammett equation.Values of ρ increase with increasing bulk of the surfactant head group and are considerably larger than in water, corresponding to decreases in micellar surface polarity.The effects of substitution of the propyl group into the phenyl and benzoyl groups show that substrate orientation at micellar surface plays no significant kinetic role.
- Bartoletti, Antonella,Bartolini, Simona,Germani, Raimondo,Savelli, Gianfranco,Bunton, Clifford A.
-
p. 723 - 728
(2007/10/02)
-
- Unimolecular rearrangements of carbanions in the gas phase. 2. Cyclopropyl anions
-
We have examined the gas-phase unimolecular rearrangements of a series of substituted cyclopropyl anions (CHXCH2CY-; X - H, Y = Ph, CHO, and CM; X = Y = CO2CH3) with a variable temperature flowing afterglow device. The ring-opening barriers range from 19 to ≥36 kcal mol-1 and are well reproduced by ab initio molecular orbital calculations. An analysis of eight monosubstituted cyclopropyl anions reveals that the flexibility (ease of inversion) and thermodynamic stability of these ions account for their tendency to isomerize.
- Chou, Phillip K.,Dahlke, Gregg D.,Kass, Steven R.
-
p. 315 - 324
(2007/10/02)
-
- ALKALINE HYDROLYSIS OF SUBSTITUTED PHENYL ACETATES CATALYZED BY QUATERNARY AMMONIUM SALTS
-
Alkaline hydrolysis of the phenyl acetates CH3COOC6H4X (X = 4-NO2, 3-NO2, 3-Cl, H, 4-CH3, 3-CH3, and 4-OCH3) in the presence of hexadecyltris(2-hydroxyethyl)ammonium chloride, bis(2-hydroxyethyl)hexadecyl(methyl)ammonium bromide, and hexadecyltrimethylamm
- Kulic, Jiri,Sussenbek, Jiri,Ptacek, Ales
-
p. 2891 - 2895
(2007/10/02)
-
- Highly Sterically hindered Carbon Acids: The Intrinsic Reactivity of 5,5',5''-Trimethyl- and 3,3',3'',5,5',5''-Hexamethyl-2,2',2'',4,4',4''-Hexanitrotriphenylmethanes
-
Rate constants (kpB,kpBH) for the reversible deprotonation of 5,5',5''-trimethyl- and 3,3',3'',5,5',5''-hexamethyl-2,2',2'',4,4',4''-hexanitrotriphenylmethanes (2 and 3) by primary aliphatic amines, piperidine and morpholine as well as by phenoxide anions and hydroxide anion have been measured in H2O-Me2SO (20:80) at 25 deg C.Comparison of the results obtained with those for 2,2',2'',4,4',4''-hexanitrotriphenylmethane (1a) shows that the introduction of methyl groups in positions adjacent to the nitro groups decreases markedly the thermodynamic acidity of theexocyclic CH group: ΔpK2a1a = 1.68; ΔpK3a1a = 6.48.It is suggested that these decreases are very likely the reflection of a twisting of the nitro groups out of their attached aromatic planes and therefore of a reduced resonance stabilization of the conjugated carbanions C-2 and C-3.Other important steric effects are operating in the ionization of 2 and 3.These arise from the accumulation of ortho-nitro groups in the triphenylmethane system which makes the approach of the base reagents from the exocyclic carbon of 2 and 3 very difficult.The finding of extremely low intrinsic reactivities for 2 and 3 and the observation of a much greater catalytic efficiency of primary amines than of secondary amines in assisting the proton transfers are the two most striking manifestations of these F-strain effects.
- Terrier, Francois,Xiao, Lan,Farrell, Patrick G.,Moskowitz, Danielle
-
p. 1259 - 1263
(2007/10/02)
-
- The Effect of Hydrogen Bonding between Methyl-Substituted Phenols and Dipolar Aprotic Solvents on the Rate Constants for Protonation of Anthracene Anion Radical
-
The kinetics for the protonation of anthracene anion radical (A-anion radical) by phenol and 13 methyl-substituted phenols (ArOH) have been studied by derivative cyclic voltammery in dimethyl sulfoxide, N,N-dimethylformamide, propylene carbonate and acetonitrile.The observed rate constants were corrected for the stoichiometric effects of formation of the homoconjugation complexes, ArOH/ArO- and Ar/OH/ArOH/ArO- and the kinetic contributions from protonation of A-anion radical by ArOH dimers.Available data for equilibrium (1) show that ArOH exists in solution predominantly as the ArOH/solvent hydrogen bond complex with only minor amounts of the 'free' ArOH present.It is suggested that the protonation of A-anion radical involves only the free ArOH in the proton transfer step (II).The unique rate constants corrected for the effect of equilibrium (I) were between two and three orders of magnitude higher than those usually referred to as the second-order rate constants for protonation of A-anion radical.ArOH/solvent ArOH + solvent (I) A-anion radical + ArOH AH-radical + ArO- (II).The kinetic effect of methyl substituents in the 2,6-positions of the phenol was observed to depend on the solvent.It was found that these effects could be satisfactority accounted for by the influence of the 2,6-methyl substituents on the magnitude of K1.The 'best' values of the substituent constants, ?b2 and ?b2.6, defined by the protonation of A-anion radical were found to be between those defined by equilibrium (1) and those defined by the unique equilibrium acidity of the phenols.This is taken as an indication that the phenol O-H bond is stretched considerably in the transition state for protonation of A-anion radical.From the relation between kII and ΔG deg it was found that the Broensted α value for the process is close to 0.5.
- Nielsen, Merete Folmer,Hammerich, Ole
-
p. 883 - 896
(2007/10/02)
-
- Ester Hydrolysis Catalysed by ortho-Palladated Aryl Oximes
-
Hydrolysis of 4-nitro- and 2,4-dinitro-phenyl carboxylates proceeds catalytically in the presence of ortho-palladated aryl oximes 4.The catalytic reaction involves two active species, identified as aquated complexes 4 with protonated (kAH path) and deprotonated (kA path) oximate groups, respectively.Both species contain a weakly basic coordinated hydroxide anion manifested in the kAH path.Other cyclopalladated hydroxo complexes 8, lacking an oxime group, are shown to react with 2,4-dinitrophenyl acetate with rate constants ca. ten times greater than those expected from their basicity.The rate constants kA obey a Broensted correlation (β ca. 1) with the pKa of the coordinated oxime group.In neutral solution, palladated oximes react with esters ca. 103 times faster than the respective free oximes.The O-acyl oxime intermediate undergoes very fast hydrolysis through intramolecular attack by the coordinated hydroxide.Factors ensuring the combination of fast acylation and deacylation steps are discussed with reference to some related systems.
- Yatsimirsky, Anatoly K.,Kazankov, Gregory M.,Ryabov, Alexander D.
-
p. 1295 - 1300
(2007/10/02)
-
- Effective Charge Development in Ester Hydrolysis Catalyzed by Cationic Micelles
-
Reaction of hydroxide ion with substituted phenyl laurates is catalyzed by micelles containing CTAB (cetyltrimethylammonium bromide).The observed rate constants for ester consumption obey a Michaelis-Menten-like rate law, kobsd = (kOHKeq + kOHcat)/(Keq + ), where kOHcat is the second order rate constant for reaction of hydroxide ion with micelle-bound ester, Keq is a partition coefficient for dissociation of ester from the micelle-bound ester, and kOH is the second order rate constant for reaction of free ester with hydroxide ion.The value of the parameter Keq is independent of the nature of the substituent on the ester.The ratio kOHcat/Keq represents the free energy change from ester in aqueous solution to the transition state of the ester reaction in the micellar pseudophase.The dependence of log kOHcat/Keq on the pKa of the leaving phenol obeys a linear Bronsted equation with β1g = -0.51, and log kOH obeys a linear Bronsted equation with β1g = -0.56.Since both Bronsted parameters refer to catalyzed and uncatalyzed reactions starting from the same standard state (aqueous solution), the effective charge in the transtition state of both reactions is almost the same.The microscopic medium is thus similar for both cases, consistent with the COOAr moiety's residing in an aqueous-like region of the pseudophase in the catalytic process.
- Al-Awadi, Nouria,Williams, Andrew
-
p. 2001 - 2004
(2007/10/02)
-
- The one-electron reduction potential of 4-substituted phenoxyl radicals in water
-
By means of pulse radiolysis the one-electron reduction potentials of twelve 4-substituted phenoxy radicals have been determined. The main reference used was the ClO2./ClO2- couple. By combining the redox potentials of phenoxyl radicals with the aqueous acidities of phenols the bond strength of the phenolic O-H bond was calculated. These values were found to be in good agreement with O-H bond dissociation enthalpies measured in the gas phase.
- Lind,Shen,Eriksen,Merényi
-
p. 479 - 482
(2007/10/02)
-
- A systematic entropy relationship for the general-base catalysis of the deprotonation of a carbon acid. A quantitative probe of transition-state solvation
-
The general-base-catalyzed deprotonation of a carbon acid, the l-methyl-4-(phenylacetyl)pyridinium cation (pKa = 9.02 at 25 °C), has been investigated for 32 general-base catalysts (25 amines and seven phenoxide ions) in aqueous solution. Amines give a generally scattered Bronsted plot; ring-substituted benzylamines have ?= 0.52, and ring-substituted phenoxides have ?= 0.60, with the phenoxides being more reactive than amines of similar basicity. The temperature dependences of the general-base-catalyzed deprotonation of this carbon acid have been measured over the range 15-45 °C for 12 base catalysts (eight primary, secondary, and tertiary amines; 4-(dimethylamino)pyridine; two phenoxide ions; hydroxide ion). The entropies of activation for these deprotonations show a clean curvilinear dependence upon the entropies of protonation of these base species, with the hydroxide ion being the only significant deviant from this relationship. This observation quantitatively establishes the importance of solvation effects as the major source of deviations that are commonly observed in Bronsted relationships for general-base-catalyzed processes.
- Bunting, John W.,Stefanidis, Dimitrios
-
p. 779 - 786
(2007/10/02)
-
- A comprehensive view of the gas-phase reaction of fluoride ions and acetic acid derivatives
-
The gas-phase reaction of F- with several acetic acid derivatives (MeCOX) is shown to proceed primarily by proton abstraction in the collision complex, rather than nucleophilic displacement, leading to the facile formation of FHX- or CH2CFO-.
- Riveros, Jose M.
-
p. 773 - 774
(2007/10/02)
-
- Eliminations from (E)-O-Arylbenzaldehyde Oximes Promoted by Hydroxide in 60 percent aq. Dimethyl Sulphoxide. Mechanism and Transition-state Characteristics of Nitrile-forming Eliminations
-
Reactions of the (E)-O-arylbenzaldehyde oximes (1; Ar = 2,4-dinitrophenyl), (2; Ar = p-nitrophenyl), and (3; Ar = phenyl) with OH- in 60 percent aq.DMSO have been investigated.The eliminations are quantitative, producing only benzonitriles and aryloxides.The observation of second-order kinetics, K2OD-/k2OH- = 1.15 - 1.84, and βlg = -0.59 is consistent with an E2 mechanism.The Hammett ρ and k2OD-/k2OH- values increased with poorer leaving groups.For a given substrate the k2OD-/k2OH- value remained (within experimental error) roughly constant, in spite of changes in the β-aryl substituents.These changes in transition state parameters can be interpreted in term of the differing nitrile-forming transition states involved.
- Cho, Bong Rae,Lee, Jong Chan,Cho, Nam Soon,Kim, Kee Dong
-
p. 489 - 492
(2007/10/02)
-
- The Gas-Phase Smiles Rearrangement: A Heavy Atom Labeling Study
-
Heavy atom ((13)C and (18)O) labeling shows that the product ion PhO- from PhO(CH2)2O- and products PhO- and PhS- from PhS(CH2)2O- are formed through Smiles intermediates I (X=Y=O or X=O, Y=S).The ana
- Eichinger, Peter C.H.,Bowie, John H.,Hayes, Roger N.
-
p. 4224 - 4227
(2007/10/02)
-
- Aminopyrine and Antipyrine Free Radical-cations: Pulse Radiolysis Studies of One-electron Transfer Reactions
-
Absolute rate constants for the reaction of a variety of electrophilic free radicals with the pyrazoline derivatives aminopyrine and antipyrine have been measured by pulse radiolysis.In the case of aminopyrine the resulting radical cation is a particularly stable species ε325 5.35*103 dm3 mol-1 cm-1).Both compounds are readily oxidised to their respective radical-cations with the one-electron oxidation potential of antipyrine (E0 1.1-1.6 V) being higher than that of aminopyrine (E0 0.26-0.5 V).Studies of the reaction of the radical-cations with reducing agents suggest that aminopyrine in particular may prove to be a useful reference compound in studies of free radical one-electron oxidations.
- Forni, Luigi G.,Mora-Arellano, Victor O.,Packer, John E.,Willson, Robin L.
-
p. 1579 - 1584
(2007/10/02)
-
- Electron Transfer From Indoles, Phenol, and Sulfite (SO32-) to Chlorine Dioxide (ClO2.)
-
With the ClO2/ClO2- couple as reference the one-electron-reduction potentials have been determined for four methylated indolyl radical cations.Their Eo values are 1.23 V (N-Me), 1.10 V (2-Me), 1.07 V (3-Me), and 0.93 V (2,3-diMe).Eo values were also measured for the following: tryptophylH.+/trypH 1.24 V, SO3.-/SO32- 0.76 V, and phenoxy./phenolate 0.80 V.The redox potentials were obtained from purely kinetic data (for tryptophan and 2-, 3-, and N-methylindole) or from combined kinetic and thermodynamic measurements.
- Merenyi, Gabor,Lind, Johan,Shen, Xinhua
-
p. 134 - 137
(2007/10/02)
-
- Generation, Thermodynamics, and Chemistry of the Diphenylcarbene Anion Radical (Ph2C.-)
-
Dissociative electron attachment with Ph2C=N produced Ph2C.- (m/z 166).The reactions of Ph2C.- with potential proton donors of known gas-phase acidity were used to bracket PA(Ph2C.-) = 380 +/- 2 kcal mol-1 from which ΔHf0(Ph2C.-) = 81.8 +/- 2 kcal mol-1 was calculated.The reactions of Ph2C.- with CH3OH and C2H5OH proceeded with major and minor amounts, respectively, of a H2.+-transfer channel, forming Ph2CH2, RCHO, and an electron.The kinetic nucleophilicity of Ph2C.- in SN2 displacement reactions with CH3X and C2H5X molecules was shown to be medium, which requires a significant intrinsic barrier in these reaction.The reactions of Ph2C.- with various aldehydes, ketones, and esters were fast and established two principal product-forming channels: (1) H+ transfer if the neutral reactant contains activated C-H bonds and (2) carbonyl addition followed by radical β-fragmentation of one of the groups originally attached to the carbonyl carbon.The order for the ease of radical β-fragmentation in the tetrahedral intermediates was RO > alkyl >> H, and CO2CH3 > CH3.Since the reactions of Ph2C.- with the simple esters HCO2CH3 and CH3CO2CH3 were fast, it should now be possible to examine the reactions of carbonyl-containing organic molecules, which are expected to react slower than these esters and obtain their relative reactivities.
- McDonald, Richard N.,Gung, Wei Yi
-
p. 7328 - 7334
(2007/10/02)
-
- Carbon-Oxygen Bond-Cleavage Reactions by Electron Transfer. 3. Electrochemical Formation and Decomposition of the Diphenyl Ether Radical Anion
-
The electrochemical reduction of diphenyl ether to its unstable radical anion was observed at -2.95 V vs.SCE in dry N,N-dimethylformamide.Kinetic studies by cyclic voltammetry and homogeneous redox catalysis techniques resulted in a first-order rate constant of 4*E5 s-1 for the decomposition of the radical anion of diphenyl ether.Controlled-potential electrolysis of diphenyl ether resulted in carbon-oxygen bond cleavage with quantitative formation of phenol and benzene.Electroreduction of diphenyl ether in the presence of D2O produced 15percent monodeuterium incorporation on benzene.The intermediacy of the phenyl radical in the cleavage pathway was tested by deploying an intramolecular radical trap, an o-(3-butenyl) substituent, on diphenyl ether.Electrochemical reduction of o-(3-butenyl)phenoxybenzene (1) in the absence of and in the presence of D2O confirmed the presence of the o-(3-butenyl)phenyl radical in the cleavage mechanism of the radical anion.Electroreduction of 1 in the presence of sodium isopropylate, a hydrogen atom donor, changed the product distribution ratio of 1-methylindan-(3-butenyl)benzene.The rate constant of the intramolecular cyclization reaction of the o-(3-butenyl)phenyl radical was estimated to be 1.5*E8 s-1.
- Thornton, Todd A.,Woolsey, Neil F.,Bartak, Duane E.
-
p. 6497 - 6502
(2007/10/02)
-