Structure–reactivity relationship for alcohol oxidations via hydride transfer to a carbocationic oxidizing agent

Second‐order rate constants were determined for the oxidation of 27 alcohols (R¹R²CHOH) by a carbocationic oxidizing agent, 9‐phenylxanthylium ion, in acetontrile at 60 °C. Alcohols include open‐chain alkyl, cycloalkyl, and unsaturated alcohols. Kinetic isotope effects for the reaction of 1‐phenylethanol were determined at three H/D positions of the alcohol (KIE_α‐D = 3.9, KIE_β‐D3 = 1.03, KIE_OD = 1.10). These KIE results are consistent with those we previously reported for the 2‐propanol reaction, suggesting that these reactions follow a hydride‐proton sequential transfer mechanism that involves a rate‐limiting formation of the α‐hydroxy carbocation intermediate. Structure–reactivity relationship for alcohol oxidations was deeply discussed on the basis of the observed structural effects on the formation of the carbocationic transition state (C^δ+? OH). Efficiencies of alcohol oxidations are largely dependent upon the alcohol structures. Steric hindrance effect and ring strain relief effect win over the electronic effect in determining the rates of the oxidations of open‐chain alkyl and cycloalkyl alcohols. Unhindered secondary alkyl alcohols would be selectively oxidized in the presence of primary and hindered secondary alkyl alcohols. Strained C₇? C₁₁ cycloalkyl alcohols react faster than cyclohexyl alcohol, whereas the strained C₅ and C₁₂ alcohols react slower. Aromatic alcohols would be efficiently and selectively oxidized in the presence of aliphatic alcohols of comparable steric requirements. This structure–reactivity relationship for alcohol oxidations via hydride‐transfer mechanism is hoped to provide a useful guidance for the selective oxidation of certain alcohol functional groups in organic synthesis. Copyright © 2011 John Wiley & Sons, Ltd.     

Systematic conformational search analysis of the SRR and RRR epimers of 7‐hydroxymatairesinol

An extensive and systematic conformational search was performed on the two epimers of the natural lignan 7‐hydroxymatairesinol (HMR), by means of a home‐made Systematic Conformational Search Analysis (SCSA) code, designed to select more and more stable conformers through sequential geometry optimization of trial structures at increasing levels of calculation theory. In the present case, the starting molecular structures were selected by the semi‐empirical AM1 method and filtered – i.e. decreased in number by choosing the more stable species – on the basis of their energy calculated by the HF method and the 6‐31G(d) basis set. The geometries obtained were further refined by performing density functional theory (DFT) optimizations, using the B3LYP functional and the 6‐31G(d,p) basis set, both in vacuo and in ethanol solution. This procedure allowed us to isolate, at a high level of theory, three groups of epimer conformers characterized by open, semi‐folded, and folded conformations. Moreover, the SCSA allowed us to describe a conformational space made‐up by about 20 species for each of the two epimers. The corresponding energy content of these species was within 27 kJ mol^?1 from the absolute minimum found, both in vacuo and in ethanol solution. The conformational analysis, followed by the inspection of the stereochemistry of the two most stable conformers of both epimers, provides support in rationalizing the proposed reaction mechanism of the catalytic hydrogenolysis of the HMR to matairesinol (MAT). Copyright © 2009 John Wiley & Sons, Ltd.     

The application of a new approach based on organic homo‐rank compounds and homologous compounds to the structure–property relationship study of mono‐substituted alkanes

The two conceptual systems of organic homologous compounds and homo‐rank compounds give insight into the influence of structures on the properties of mono‐substituted alkanes X_i–(CH₂)_j–H from the transverse (change of repeating unit number j of CH₂) and longitudinal (change of functional group X_i) perspectives, respectively. This paper aims to combine the organic homo‐rank compounds approach together with the homologous compounds approach to explore the property change rules of mono‐substituted alkanes involving various substituents. Firstly, based on the concept of organic homologous compounds, the properties of mono‐substituted straight‐chain alkane homologues were linearly correlated to the two‐thirds power of the number of carbon atoms (N^2/3) in alkyl, and regression equations such as Q = A + BN^2/3 were obtained. The regression coefficients A and B vary with different substituents X_i, so coefficients A and B were employed to characterize the structural information of substituent X_i. The structural features of alkyls (–(CH₂)_j–H, that is, –C_jH_2j+1) were described by the polarizability effect index (PEI_(R)) and vertex degree–distance index (VDI). Then based on four parameters A, B, PEI_(R), and VDI, quantitative structure–property relationship models were built for the boiling points (Bp) and refractive indexes (n_D) of each mono‐substituted alkane homo‐rank series, where j = 3–10 and the substituents X_i involve F, Cl, Br, I, NO₂, CN, NH₂, COOH, CHO, OH, SH, and NC. Good results indicate that the combination of an organic homo‐rank compounds method and a homologous compounds method has exhibited obvious advantages over traditional methods in the quantitative structure–property relationship study of mono‐substituted alkanes concerning various substituents. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantitative structure-activity relationship studies on some series of calcium channel blockers

A quantitative structure-activity relationship (QSAR) study has been made on four different series of dihydropyrimidine analogs that mimic the most widely studied class of calcium channel blockers (CCBs)-the 1,4-dihydropyridine (DHP) class. The results show that almost all those characteristics that are essential for the activity of 1,4-DHPs are also essential for the activity of dihydropyrimidine analogs. The important characterstics indicated by the present study for dihydropyrimidine analogs are conformation of the molecule, the relative orientation of the aryl ring with respect to the pyrimidine ring, and some substituents capable of forming the hydrogen bonds with the receptor but less bulky in nature, and high molar refractivity of the molecule.     

Intramolecular Diels–Alder reaction in enyne–allenes: a computational investigation and comparison with the Myers–Saito and Schmittel reactions

The reaction mechanisms as well as substituted effect and solvent effect of the enyne–allenes are investigated by Density Functional Theory (DFT) method and compared with the Myers–Saito and Schmittel reactions. The Myers–Saito reaction of non‐substituted enyne–allenes is kinetically and thermodynamically favored as compared to the Schmittel reaction; while the concerted [4 + 2] cycloaddition is only 1.32 kcal/mol higher than the C₂? C₇ cyclization and more exothermic (Δ_RE = ?69.38 kcal/mol). For R₁ = CH₃ and t‐Bu, the increasing barrier of the C₂? C₇ cyclization is higher than that for the C₂? C₆ cyclization because of the steric effect, so the increased barrier of the [4 + 2] cycloaddition is affected by such substituted electron‐releasing group. Moreover, the strong steric effect of R₁ = t‐Bu would shift the C₂? C₇ cyclization to the [4 + 2] cycloaddition. On the other hand, for R₁ = Ph, NH₂, O^?, NO₂, and CN substituents, the barrier of the C₂? C₆ cyclization would be more diminished than the C₂? C₇ cyclization due to strong mesomeric effect; the reaction path of C₂? C₇ cyclization would also shift to the [4 + 2] cycloaddition. The solvation does not lead to significant changes in the potential‐energy surface of the reaction except for the more polar surrounding solvent such as dimethyl sulfoxide (DMSO), or water. Copyright © 2009 John Wiley & Sons, Ltd.     

Surfactant‐assisted specific‐acid catalysis of Diels–Alder reactions in aqueous media

Surfactant‐assisted specific‐acid catalysis (SASAC) for Diels–Alder reactions of dienophiles 1 and 4 with cyclopentadiene 2 in aqueous media at 32 °C was studied. This study showed that acidified anionic surfactants (pH 2) such as sodium dodecyl sulfate (SDS) and linear alkylbenzene sulfonic acid (LAS) accelerate Diels—Alder reactions. Conversely, under similar reaction conditions (pH 2) these reactions are inhibited by (acidified) cationic surfactants such as dodecyltrimethylammonium bromide (DTAB), dodecyldimethylammonium bromide (DDAB), and dodecylmethylammonium bromide (DMAB). A modest rate acceleration resulting from the surfactant hydrogen‐bonding capacity is also recorded for the Diels–Alder reaction of naphthoquinones ( 6 ) with cyclopentadiene ( 2 ) in aqueous media at 32 °C. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of substituent groups of porphyrins on the electroluminescent properties of porphyrin‐doped OLED devices

Six tetraphenylporphyrins (TRPPH₂) with different horizontal substituents R (R = H, CH₃, OH, F, Cl, Br) were synthesized, and the organic light‐emitting diode (OLED) devices with a general configuration of ITO/TPD/Alq₃:2%TRPPH₂/Alq₃/Al were prepared. The substituted TRPPH₂ was used as the host dopant, 4,4‐bis‐(m‐tolyphenylamino)biphenyl (TPD) was used as a hole‐transporting material, and aluminum tris(8‐quinolinolato) (Alq₃) was used as an electron‐transporting material. The electroluminescent (EL) properties of these devices were studied to understand the light emitting properties of the substituted TRPPH₂. Previous studies have found that the color emitted by the devices was dependent on the TRPPH₂ dye concentration. The electronic effect of the horizontal substituents R of TRPPH₂ influenced the turn‐on voltage, brightness, and power efficiency of the devices. Also, the electroluminescence performance of the porphyrin‐doped OLED devices depended on the effectual overlaps between the emission of electron‐transporting material and the absorption of the dopants. This means that it is possible to evaluate the electroluminescence performance of the porphyrin‐doped OLED devices based on the emission of electron‐transporting material and the absorption of the dopants. Copyright © 2009 John Wiley & Sons, Ltd.     

Kinetics of pi‐complex isomerization during AlCl3‐catalyzed Friedel–Crafts reactions between linear olefins and p‐xylene

Rapid isomerization of pi‐complex intermediates results in the formation of multiple isomers of alkyl aromatics during AlCl₃‐catalyzed reactions between linear olefins and aromatic rings. The authors present results of a kinetic study of reactions between p‐xylene, 1‐dodecene, and linear tetradecenes. Product distributions are well predicted based on a model of reversible pi‐complex isomerization. Surprisingly, no double bond isomerization was observed in the linear olefins: All isomerization occurred in the pi‐complexes. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of microheterogeneity of CF3CH2OH–H2O mixed solvent on reactions of carbocations from 1,2,2,3‐tetramethyl‐1,2‐dihydroquinoline

Carbocations are key intermediates in many important organic reactions. The remarkable effect of the solvent composition on the kinetic parameters of the carbocation decay and product composition was found in the photolysis of 1,2,2,3‐tetramethyl‐1,2‐dihydroquinoline ( 1 ) in 2,2,2‐trifluoroethanol (TFE)–H₂O mixtures. The rate constant of the intermediate carbocation decay has a maximum, and the activation energy is minimal in the TFE–H₂O mixture 3 : 7 (v/v). In the steady‐state photolysis, products of oligomerization of 1 with n up to 8 and their adducts with TFE and H₂O were identified at this solvent composition. The results were rationalized in terms of TFE clustering in aqueous mixtures, with the maximum of cluster formation at 30 vol % TFE. The clusters form a pseudo‐phase, in which the molecules of 1 are concentrated and the carbocations are generated. TFE, H₂O and 1 compete in the combination reaction with the photogenerated carbocation to afford the products. This effect was not observed for 1,2,2,4‐tetramethyl‐1,2‐dihydroquinoline ( 2 ), the isomer of 1 , due to steric hindrance at C(4) carbon atom of the heterocycle, the active site of the intermediate carbocation, which makes impossible for the carbocation from 2 to react further with 2 . Thus, the kinetic parameters and the product composition in the photolysis of 1 in TFE–H₂O mixtures reflect the changes in the microstructure of the binary solvent. Copyright © 2013 John Wiley & Sons, Ltd.     

The influence of indium on the structural modification of the amorphous Ge–In–Se system

The effect of both the chemical composition and the nature of the chemical bonding of amorphous alloyed samples of Ge_xIn_ySe_100−x−y prepared under vacuum with x=20, 4y15 on the efficiency of the structural modification Δφ is analysed using a simple consideration based on the coordination number Z, and the number of topological constraints N_co. The previously obtained parameters have been used for the determination of the number of continuous deformation (i.e. zero-frequency modes f ), and for the estimation of the cohesive energies of these glasses, assuming simple additivity of bond energies. A trial has been made to correlate the results of this paper with the previously published data of glass transition temperature T_g, activation energy ₀ and the shift of the K-absorption edge (ΔE_K) of the composition of vacuum prepared Ge_xIn_ySe_100−x−y. It was found that there is a correlation between the lone-pair electrons and the stability of the vitreous state. According to the criterion of Liang, the above correlation has been interpreted in terms of Δφ.     

Solvent effects in the reaction between (anthracen‐9‐yl)methyl sulfides and electron‐deficient acetylenes

Solvent‐dependent diverse reactivity of (anthracen‐9‐yl)methyl sulfides with a few electron‐deficient acetylenes is described. Diversity in reactivity is attributed to competition between one electron transfer, two electron transfer and Diels–Alder reaction of these sulfides with electron‐deficient acetylenes. We have proposed plausible mechanisms to account for various reactions observed by us. Copyright © 2015 John Wiley & Sons, Ltd.     

Current–phase relationship measurements in the flow of superfluid He through a single orifice

We report accurate measurements of the current-phase relationship in the flow of superfluid ³He through a single orifice. While ideal sinusoidal 2π-periodic Josephson behavior prevails close to T_c, increasingly strong π-periodic admixture is usually observed at lower temperatures.     

First order reversal curves analysis of the temperature effect on magnetic interactions in barium ferrite with La–Co addition

First order reversal curves (FORCs) distributions are a powerful tool for investigating hysteresis and interactions in magnetic systems and have been widely applied. La–Co substitution in barium hexaferrites has also been extensively studied. The most effective substitution to improve the magnetic properties (coercive field and energy product) is given by x=y=0.2 in the formula Ba_1-xLa_xFe_12-yCo_yO₁₉. In this work, this stoichiometry is initially used to obtain a state where more than one phase is present. The magnetic behavior as a function of temperature was studied in order to have an insight into the magnetic interactions that originate a decrease in the magnetic performance of Ba hexaferrite magnets. The sample was structurally characterized by X-ray diffraction (XRD) and magnetically studied in a SQUID magnetometer. FORC distributions were used to study the dependence of the magnetic interactions with the temperature. FORC diagrams performed on the sample at different temperatures exhibit similar characteristics, such as the spread in the h_c–h_u plane and a spread out of the h_c-axes. These features are interpreted in terms of exchange-interacting particles and dipolar interactions, respectively. As the temperature decreases, stronger interactions are noticed among hard and soft phases.     

Dynamics and Recovery of Genuine Multipartite Einstein–Podolsky–Rosen Steering and Genuine Multipartite Nonlocality for a Dissipative Dirac System via the Unruh Effect

The dynamics behaviors of genuine multipartite Einstein–Podolsky–Rosen steering (GMS) and genuine multipartite nonlocality (GMN) are investigated herein, and how the lost GMS and GMN under a mixed decoherence system can be recovered is explored. Explicitly, the decoherence system can be modeled by that a tripartite Werner‐type state suffers from the non‐Markovian regimes and one subsystem of the tripartite is under a non‐inertial frame. The conditions for steerable and nonlocal states can be obtained with respect to the tripartite Werner‐type state established initially. GMS and GMN are very fragile and vulnerable under the influence of the collective decoherence. GMS and GMN will vanish with growing intensity of the Unruh effect and the non‐Markovian reservoir. Besides, all achievable GMN's states are steerable, while not every steerable state (GMS's state) can achieve nonlocality. This means that the steering–nonlocality hierarchy is still tenable and GMN's states are a strict subset of the GMS's states in such a scenario. Subsequently, an available methodology to recover the damaged GMS and GMN is proposed. It turns out that the lost GMS and GMN can be effectively restored, and the ability of GMS and GMN to suppress the collective decoherence can be enhanced.     

Substituent‐induced regioselective hydroxylation of the aromatic C–H bond on naphthalene with metachloroperbenzoic acid catalyzed by F20TPPMnCl

The regioselective hydroxylation of the aromatic C–H bond on a series of naphthalenes with different β‐substituent R (R = H, Me, Et, i‐Pr, OMe, COOH, Br, etc.) was studied, and the substituent effect on the regioselectivity was investigated. The electron‐donating substituent afforded the aromatic C–H bond hydroxylation at the 1α position with more than 80% selectivity, while the electron‐withdrawing substituent afforded the aromatic C–H bond hydroxylation at the 4α position with more than 60% selectivity of β‐substituted naphthalene hydroxylated with metachloroperbenzoic acid catalyzed by tetrakis(pentafluorophenyl)porphyrin manganese(III) chloride. The research showed that the steric and electronic effects of the substituent appeared to play a significant role in determining the regioselectivity, and the electronic effect was of more importance than the steric effect of the substituent in the current situation. The studies may provide additional proofs for the stepwise mechanism of the aromatic C–H bond hydroxylation through a cationic intermediate. Copyright © 2012 John Wiley & Sons, Ltd.     

Substituent effects in the Diels–Alder reactions of butadienes,cyclopentadienes, furans and pyroles with maleic anhydride

In this study, activation energies in the Diels–Alder reactions of a series of substituted butadienes, cyclopentadienes, furans and pyroles with maleic anhydride were calculated by the M06‐2X/6‐31G(d) method. The substituent effects on the reactivity and the endo–exo selectivity have been examined. The strength of reactivity effect has an order of pyroles > furans > cyclopentadienes > butadienes, which is highly correlated with the lowest unoccupied molecular orbital energy, the electronic chemical potential and the electrophilicity of parent diene but relatively less correlated with the highest occupied molecular orbital energy and chemical hardness. The trend that an increase of necleophilicity caused by an electron‐donating group on the diene favors the endo TS is effective with C2 substitution. With C1 substitution, the trend is ambiguous or even opposite. Copyright © 2015 John Wiley & Sons, Ltd.