Reactivities of mixed organozinc and mixed organocopper reagents. Part 7. Comparison of the transfer rate of the same group in allylation of mixed and homo diorganozinc reagents

A detailed direct kinetic study has been carried out to compare the reaction rate of transferable group, Ph in mixed phenylzinc reagents, RPhZn (R = n‐alkyl) and in homo diphenylzinc reagent, Ph₂Zn in their reactions with allyl bromide in THF at 25–(?15) °C. Empirical rata law and activation parameters are consistent with a second‐order substitution reaction. The allylation rate of transferable group Ph in RPhZn (R = n‐alkyl) has been found higher than the rate of Ph group in Ph₂Zn. A mechanism which accommodates the kinetic data and higher allylation rate of transferable group Ph in RPhZn than that in Ph₂Zn is given. Copyright © 2013 John Wiley & Sons, Ltd.     

Reactivity of mixed organozinc and mixed organocopper reagents. Part 4: a kinetic study of group transfer selectivity in C?C coupling of mixed diorganocuprates

The competitive rate data and Taft relationships for the coupling of bromomagnesium n‐butyl (substituted phenyl) cuprates with alkyl bromides show that selective n‐butyl transfer can be explained by an oxidative addition mechanism. Taft reaction constants also show that the residual group FG‐C₆H₄ in the mixed cuprate n‐Bu(FG‐C₆H₄)CuMgBr changes the ability of the copper nucleophile to react with the electrophile RBr. These results provide support for the commonly accepted hypothesis regarding the dependence of the R¹ group transfer ability on the strength of R²? Cu bond in reactions of R¹R²CuMgBr reagents. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrasonic detection of hydrophobic interactions: a quantitative approach

Kinetic effects of sonication on ester hydrolysis and tert‐butyl chloride solvolysis, studied in ethanol–water binary solvent, are discussed in terms of quantitative relationships between their magnitude and the hydrophobicity of reagents. A number of conclusions were drawn from the observed linear free‐energy (LFE) relationships. Independent of reaction mechanism, the decrease in reaction rates with increasing ethanol content in the solvent is mainly due to hydrophobic stabilization of the ground state. While hydrophobic species can be hidden in the ethanol clusters present in the region X_EtOH > 0.15, at lower ethanol contents hydrophobic reagents are weakly solvated and the hydrophobic stabilization can be easily overcome by sonication. Copyright © 2008 John Wiley & Sons, Ltd.     

Bent-shaped mesogenic oxadiazoles and thiadiazoles with terminal methyl group

Rod-shaped 4-methylbenzoic acid-N′-(4′-n-alkoxybenzoyl) hydrazide (series I) have been synthesized by the Schotten–Baumann reaction of 4-methylbenzhydrazide with 4-n-alkoxy benzoyl chloride using dry pyridine, as a solvent. The series I compounds have been cyclized to bent-shaped mesogenic 2-(4′-methylphenyl)-5-(4″-n-alkoxyphenyl)-1,3,4-oxadiazoles (series II) and 2-(4′-methylphenyl)-5-(4″-n-alkoxyphenyl)-1,3,4-thiadiazole (series III) using POCl₃ and Lawesson's reagent, respectively. The synthesized compounds are characterized by the combination of elemental analysis and standard spectroscopic methods. In series II, lower and middle members are non-mesogenic. n-Dodecyloxy to n-hexadecyloxy derivatives exhibit enantiotropic nematic mesophase. In series III, all the compounds synthesized exhibit enantiotropic nematic mesophase. n-Tetradecyloxy and n-hexadecyloxy derivatives also exhibit enantiotropic SmA mesophase. The mesomorphic properties of the series II and III used in this study are compared with each other and with other structurally related compound to evaluate the effect of different heterocyclic moieties as well as terminal substituents on mesomorphism.     

Electrochemical reduction of benzoyl chloride to benzil in ionic liquid BMIMBF4

A new electrochemical procedure for the electrocatalytic dimerisation of benzoyl chloride in ionic liquid, 1‐butyl‐3‐methylimidazoliumtetrafluoborate, to benzil was investigated for the first time. The electrochemical behavior of benzoyl chlorides in BMIMBF₄ was studied by cyclic voltammetry with a reduction peak at ?1.2 V (vs Ag). The electrolysis experiments were carried out in an undivided cell under mild conditions without any toxic solvents, catalysts and supporting electrolytes, creating benzil at a moderate yield (51%). The results showed that the yields were strongly affected by various factors: temperature, working potential, electrode material. Moreover, the ionic liquid was successfully recycled for this reaction. Copyright © 2011 John Wiley & Sons, Ltd.     

Variation of the temperature‐dependent substituent effects with solvent in alkaline hydrolysis of substituted phenyl and alkyl benzoates and phenyl tosylates

The second‐order rate constants k for the alkaline hydrolysis of eight substituted alkyl benzoates have been measured spectrophotometrically in aqueous 5.3 M NaClO₄ and 0.5 M n‐Bu₄NBr at various temperatures. Variation of the substituent effect with temperature in alkaline hydrolysis of ortho‐, meta‐, and para‐substituted phenyl benzoates, phenyl tosylates, and alkyl benzoates in various solvents (water, aqueous 0.5 M Bu₄NBr, 80% (v/v) DMSO, 2.25 M Bu₄NBr, and 5.3 M NaClO₄) was studied. The susceptibility to temperature variation of the meta and para polar substituent effect, the ortho inductive effect, and the alkyl polar effect for various media showed good correlation with the solvent electrophilicity, E_S, which characterizes the hydrogen‐bond donating power of the solvent. The variation of the temperature‐dependent ortho inductive effect with solvent hydrogen‐bond donor capacity (electrophilicity) was found to be nearly twice smaller than that for meta and para polar effect. The temperature‐dependent alkyl polar substituent effect was found to vary with E_S nearly by the same extent as the polar effect of meta and para substituents. The dependences of the ρ values (altogether 109 values of ρ) on the (1/T) term for various media were found to cross nearly at the same isosolvent temperature (1/β_isosolv ≈ 2 × 10^?3) for meta‐, para‐, ortho‐, and alkyl‐substituted esters. At T = β_isosolv the difference (ρ)_S ? (ρ)_Water becomes zero for all polar substituent effects in all media considered and the additional inductive effect from the ortho position (compared with para derivatives) disappears for all solvents studied. Copyright © 2007 John Wiley & Sons, Ltd.     

Morphology of Fractured Polymer‐Polymer Interfaces Bonded at Ambient Temperature as Studied by Atomic Force Microscopy

The amorphous polymer surfaces of polystyrene (PS, M _n=200 kg/mol, M _w/M _n=1.05) and poly(methyl methacrylate) (PMMA, M _n=51.9 kg/mol, M _w/M _n≤1.07) were brought into contact at 21°C to form PS‐PS (for 54 days) and PMMA‐PMMA auto‐adhesive joints (for 11 days). After contact at that temperature corresponding to T _g‐bulk ?81°C for PS and to T _g‐bulk–88°C for PMMA, where T _g‐bulk is the calorimetric glass transition temperature of the bulk sample, the bonded interfaces were fractured and their surfaces were analyzed by atomic force microscopy (AFM). The surface roughness, R _q, of the fractured interfaces was larger by a factor of 3–4 than was that of the free PS and PMMA surfaces aged for the same period of time. A similar increase in R _q was found by comparison of the free PS surface aged at T _g‐bulk+15°C for 1 h and of the surface of the PS‐PS interface fractured after healing at T _g‐bulk+15°C for 1 h. These observations, indicative of the deformation of the fractured interfaces, suggest the occurrence of some mass transfer across the interface even below T _g‐bulk ?80°C.     

Positioning solvolyses within the SN2‐SN1 and SN3‐SN2 spectrum of reaction mechanisms

A simple linear regression (Q equation) is devised to position solvolyses within the established S_N2‐S_N1 spectrum of solvolysis mechanisms. Using 2‐adamantyl tosylate as the S_N1 model and methyl tosylate as the S_N2 model, the equation is applied to solvolyses of ethyl, allyl, secondary alkyl and a range of substituted benzyl and benzoyl tosylates. Using 1‐adamantyl chloride as the S_N1 model and methyl tosylate as the S_N2 model, the equation is applied to solvolyses of substituted benzoyl chlorides in weakly nucleophilic media. In some instances, direct correlations with methyl tosylate were employed. Grunwald–Winstein l values and kinetic solvent isotope effects are also used to locate solvolyses within the spectrum of mechanisms. Product selectivities (S) for solvolyses at 50 °C of p‐nitrobenzyl tosylate in binary mixtures of alcohol–water and of alcohol–ethanol for five alcohols (methanol, ethanol, 1‐propanol and 2‐propanol and t‐butanol) are reported and show the expected order of solvent nucleophilicity (RCH₂OH > R₂CHOH > R₃COH). The data support the original assignments establishing the N_OTs scale of solvent nucleophilicity. Copyright © 2016 John Wiley & Sons, Ltd.     

The leaving group dependence in the rates of solvolysis of 1,2‐diphenylethyl system

1,2‐Diphenylethyl chloride undergoes solvolysis by S_N1 mechanism in aqueous organic solvents. The α‐phenyl group of 1,2‐diphenylethyl chloride enters into conjugation with the developing carbocationic centre. The β‐phenyl group on the other hand was unable to extend its conjugation via neighbouring group participation due to steric inhibition of resonance in the formation of non‐classical carbocation. 1,2‐Diphenylethyl chloride thus behaves similar to 1‐phenylethyl chloride in its solvolysis pattern. The solvolytic rate studies of chloride and methanesulphonate of 1,2‐diphenylethyl alcohol in various aqueous organic solvents show that the dispersion observed in the Winstein–Grunwald plot is not due to a change in leaving group but due to the difference in solvation requirements of aromatic and aliphatic groups. Copyright © 2010 John Wiley & Sons, Ltd.     

Ionic conductivity of highly deproteinized natural rubber having various amount of epoxy group mixed with lithium salt

Ionic conductivity of highly deproteinized natural rubber having various amount of epoxy group (LEDPNR) mixed with lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) salt was investigated through impedance analysis with respect to salt concentration, glass transition temperature and epoxy group content. The LEDPNR was prepared from depolymerization of epoxidized natural rubber (ENR) latex, which was prepared by deproteinization of natural rubber latex with proteolytic enzyme and surfactant followed by epoxidation with fresh peracetic acid. The resulting LEDPNR was found to have 10–57 mol% epoxy group, low M_n and low T_g. The conductivity of LEDPNR/LiTFSI mixture was dependent on LiTFSI salt concentration and glass transition temperature (T_g). The highest ionic conductivity versus salt concentration for the mixtures was found to be due to amount of effective carrier ion and the highest mobility of segment of LEDPNR at a suitable LiTFSI concentration. The ionic conductivity of LEDPNR/LiTFSI mixtures was further dependent on epoxy group content.     

Determination of <Superscript>68</Superscript>Ga production parameters by different reactions using ALICE and TALYS codes

Gallium-68 (T _1/2 = 68 min, I _β+ = 89%) is an important positron-emitting radionuclide for positron emission tomography and used in nuclear medicine for diagnosing tumours. This study gives a suitable reaction to produce ⁶⁸Ga. Gallium-68 excitation function via ⁶⁸Zn(p, n)⁶⁸Ga, ⁶⁸Zn(d, 2n)⁶⁸Ga, ⁷⁰Zn(p, 3n)⁶⁸Ga and ⁶⁵Cu(α, n)⁶⁸Ga reactions were calculated by ALICE-91 and TALYS-1.0 codes. The calculated excitation function of ⁶⁸Zn(p, n)⁶⁸Ga reaction was compared with the reported measurement and evaluations. Requisite thickness of the targets was obtained by SRIM code for each reaction. The ⁶⁸Ga production yield was evaluated using excitation function and stopping power.      

Effect of the structure of nitroxyl radicals on the kinetics of their acid‐catalyzed disproportionation

Acid‐catalyzed disproportionation of cyclic nitroxyl radicals R₂NO^? includes the half‐reactions of their oxidation to oxoammonium cations R₂NO⁺ and reduction to hydroxylamines R₂NOH. For many nitroxyl radicals, this reaction is characterized by its ~100% reversibility. Quantitative characteristics of acid–base and redox properties of the whole redox triad may be obtained from research of kinetics and equilibrium of this reaction. Here, we have examined the kinetics for the disproportionation of twenty piperidine‐, pyrroline‐, pyrrolidine‐, and imidazoline nitroxyl radicals in aqueous H₂SO₄, and interpreted it in terms of the excess acidity function X. The rate‐limiting step of this reaction is R₂NO^? oxidation by its protonated counterpart R₂NOH^+?. Kinetic stability of R₂NO^? in acidic media depends on the basicity of nitroxyl group. This basicity is influenced predominantly by protonation of another, more basic group in radical structure, and its proximity to nitroxyl group. The discovered estimates of pK values for radical cations R₂NOH^+? (from ?5.8 to ?12.0) indicate a very low basicity of nitroxyl groups in all commonly used R₂NO^?. For the first time, a linear correlation is obtained between the one‐electron reduction potentials of oxoammonium cations and the basicity of nitroxyl groups of related radicals. Copyright © 2013 John Wiley & Sons, Ltd.     

Solvent effects on chemical processes: new solvents designed on the basis of the molecular–microscopic properties of (molecular solvent + 1,3‐dialkylimidazolium) binary mixtures

The purpose of this work was to analyze the microscopic feature of binary solvent systems formed by a molecular solvent (acetonitrile or dimethylformamide or methanol) and an ionic liquid (IL) cosolvent [1‐(1‐butyl)‐3‐methylimidazolium tetrafluoroborate or 1‐(1‐butyl)‐3‐methylimidazolium hexafluorophosphate]. The empirical solvatochromic solvent parameters E_T(30), π*, α, and β were determined from the solvatochromic shifts of adequate indicators. The behavior of the solvent systems was analyzed according to their deviation from ideality. The study focused on the identification of solvent mixtures with relevant solvating properties in order to select mixed solvents with particular characteristics. The comparison of the molecular–microscopic solvent parameters corresponding to the selected binary mixtures with both ILs considered at similar mixed‐solvent composition revealed that the difference is centered on the basic character of them. A kinetic study of a nucleophilic aromatic substitution reaction between 1‐fluoro‐2,4‐dinitrobenzene (FDNB) and 1‐butylamine (BU) developed in (acetonitrile or dimethylformamide + IL) solvent mixtures is presented in order to investigate and compare the solvent effects on a chemical process. For the explored reactive systems the solvation behavior is dominated by both the dipolarity/polarizability and the basicity of the media, contributing these solvent properties to accelerating the chemical process. Copyright © 2007 John Wiley & Sons, Ltd.     

The protective effect of hydroxyl‐substituted Schiff bases on the radical‐induced oxidation of DNA

The protective effects of 18 hydroxyl‐substituted Schiff bases (SchOHs) on the oxidative damage of naked DNA induced by 2,2′‐azobis(2‐amidinopropane hydrochloride) (AAPH) were reported, in which SchOHs were prepared by condensing hydroxyl‐substituted aromatic aldehydes and anilines. The extent of the oxidative damage of DNA was followed by measuring the formation of thiobarbituric acid reactive substance (TBARS). Some SchOHs bearing only one hydroxyl group (prepared by salicylic aldehyde) protected DNA by decreasing the formation rate of TBARS. Other SchOHs inhibited the oxidation of DNA for a period, resulting in an inhibition period (t_inh) that was proportional to the concentration of SchOH, viz., t_inh = (n/R_i)[SchOH]. Thus, the stoichiometric factor (n) can be calculated if the initiation rate (R_i) was known. The n value of an SchOH was closed to the summation of the n from every structural feature in this SchOH, indicating that the antioxidant activity of SchOH was contributed from every structural feature in the molecule. Furthermore, the large conjugative system and para‐hydroxyl at benzilidene were good for the antioxidant activity of SchOHs. Copyright © 2009 John Wiley & Sons, Ltd.     

Theoretical calculations for neighboring group participation in gas‐phase elimination kinetics of 2‐hydroxyphenethyl chloride and 2‐methoxyphenethyl chloride

Theoretical calculation of the kinetics and mechanisms of gas‐phase elimination of 2‐hydroxyphenethyl chloride and 2‐methoxyphenethyl chloride has been carried out at the MP2/6‐31G(d,p), B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(d,p), B3PW91/6‐31G(d,p) and CCSD(T) levels of the theory. The two substrates undergo parallel elimination reactions. The first process of elimination appears to proceed through a three‐membered cyclic transition state by the anchimeric assistance of the aromatic ring to produce the corresponding styrene product and HCl. The second process of elimination occurs through a five‐membered cyclic transition state by participation of the oxygen of o‐OH or the o‐OCH₃ to yield in both cases benzohydrofuran. The B3PW91/6‐31G(d,p) method was found to be in good agreement with the experimental kinetic and thermodynamic parameters for both substrates in the two reaction channels. However, some differences in the performance of the different methods are observed. NBO analysis of the pyrolysis of both phenethyl chlorides implies a C? Cl bond polarization, in the sense of C^δ+…Cl^δ?, which is a rate‐determining step for both parallel reactions. Synchronicity parameters imply polar transition states of these elimination reactions. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of ortho substituents on carbonyl carbon 13C NMR chemical shifts in substituted phenyl benzoates

¹³C NMR spectra of 37 ortho‐, meta‐, and para‐substituted phenyl benzoates, containing substituents in benzoyl and phenyl moiety, 4 ortho‐substituted methyl and 5 ethyl benzoates as well as 9 R‐substituted alkyl benzoates have been recorded. The influence of the ortho substituents on the carbonyl carbon ¹³C NMR chemical shift, δ_CO, was found to be described by a linear multiple regression equation containing the inductive, σ_I, resonance, σ°_R, and steric, E, or υ substituent constants. For all the ortho‐substituted esters containing substituents in the acyl part as well as the phenyl part, the substituent‐induced reverse inductive effect (ρ_I < 0), the normal resonance effect (ρ_R > 0), and the negative steric effect (δ_ortho < 0) with the E were observed. In the case of ortho substituents in the phenyl part, the resonance effect was negligible. Due to inductive effect, the ortho electron‐withdrawing substituents showed an upfield shift or shielding of the carbonyl carbon, while the electron‐donating substituents had an opposite effect. Because of the sterical consequences, ortho substituents revealed a deshielding effect on the ¹³C NMR chemical shift of the carbonyl carbon. For all the meta‐ and para‐substituted esters, the reverse substituent‐induced inductive and resonance effects (ρ_I < 0, ρ_R < 0) were found to be significant. In alkyl benzoates, the alkyl substituents showed the reverse inductive and steric effects. The log k values for the alkaline hydrolysis in water, aqueous 0.5 M Bu₄NBr and 2.25 M Bu₄NBr, and the IR frequencies, ν_CO, for the ortho‐, meta‐, and para‐substituted phenyl benzoates and alkyl benzoates were correlated nicely with the corresponding ¹³C NMR substituent chemical shifts, Δδ_CO. Copyright © 2009 John Wiley & Sons, Ltd.     

A theory of generally invariant lagrangians for the metric fields. I

The second-order generally invariant Lagrangians for the metric fields are studied within the framework of the Ehresmann theory of jets. Such a Lagrangian is a function on an appropriate fiber bundle whose structure group is the groupL _n ³ of invertible 3-jets with source and target at the origin 0 of the real,n-dimensional Euclidean spaceR ⁿ, and whose type fiber is the manifold T_n ²(R^n* R ^n*) of 2-jets with source at 0 R ⁿ and target in the symmetric tensor productR ^n* R^n*. Explicit formulas for the action ofL _n ³ onT _n ²(R^n* R ^n*) are considered, and a complete system of differential identities for the generally invariant Lagrangians is obtained.     

Homo‐Diels–Alder reaction of a very inactive diene,bicyclo[2,2,1]hepta‐2,5‐diene,with the most active dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione. Solvent,temperature, and high pressure influence on the reaction rate

Solvent, temperature, and high pressure influence on the rate constant of homo‐Diels–Alder cycloaddition reactions of the very active hetero‐dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione (1), with the very inactive unconjugated diene, bicyclo[2,2,1]hepta‐2,5‐diene (2), and of 1 with some substituted anthracenes have been studied. The rate constants change amounts to about seven orders of magnitude: from 3.95^.10^?3 for reaction (1+2) to 12200 L mol^?1 s^?1 for reaction of 1 with 9,10‐dimethylanthracene (4e) in toluene solution at 298 K. A comparison of the reactivity (ln k₂) and the heat of reactions (?_r‐nH) of maleic anhydride, tetracyanoethylene and of 1 with several dienes has been performed. The heat of reaction (1+2) is ?218 ± 2 kJ mol^?1, of 1 with 9,10‐dimethylanthracene ?117.8 ± 0.7 kJ mol^?1, and of 1 with 9,10‐dimethoxyanthracene ?91.6 ±0.2 kJ mol^?1. From these data, it follows that the exothermicity of reaction (1+2) is higher than that with 1,3‐butadiene. However, the heat of reaction of 9,10‐dimethylanthracene with 1 (?117.8 kJ mol^?1) is nearly the same as that found for the reaction with the structural C=C counterpart, N‐phenylmaleimide (?117.0 kJ mol^?1). Since the energy of the N=N bond is considerably lower (418 kJ/bond) than that of the C=C bond (611 kJ/bond), it was proposed that this difference in the bond energy can generate a lower barrier of activation in the Diels–Alder cycloaddition reaction with 1. Linear correlation (R = 0.94) of the solvent effect on the rate constants of reaction (1+2) and on the heat of solution of 1 has been observed. The ratio of the volume of activation (?V^≠) and the volume of reaction (?V_r‐n) of the homo‐Diels–Alder reaction (1+2) is considered as “normal”: ?V^≠/?V_r‐n = ?25.1/?30.95 = 0.81. Copyright © 2012 John Wiley & Sons, Ltd.     

Announcement

The He(I) and He(II) photoelectron spectra of benzoyl chloride have been subjected to a relative band intensity analysis. The spectral assignment, which is supported by theoretical ionization cross-sections calculated from a GAUSSIAN 70 wavefunction, illustrates the use of He(II) radiation for molecules containing heavy atoms. The low ionization potentials of benzoyl chloride are described in molecular orbital terms as π < π < n_o < n_C? ～ ⁿ_Cl.