Showing papers in "International Journal of Molecular Sciences in 2005"

Relation of Certain Quantum Chemical Parameters to Lubrication Behavior of Solid Oxides

Abstract: It is well-documented that certain oxides (such as Re2O7, B2O3, MoO3, V2O5, etc.) can provide friction coefficients of 0.1-0.3 to sliding surfaces at elevated temperatures and thus they are often referred to as lubricious oxides in the tribology literature. In a recently proposed crystal chemical model, Erdemir was able to establish a close correlation between the reported friction coefficients of such oxides and their ionic potentials [1]. In the present paper, we expand on this original concept and explore the relevance of two other quantum chemical parameters, electronegativity and chemical hardness, to the lubricity of solid oxides. These parameters have already been used by scientists to explain the nature of tribochemical interactions between various oil additives and sliding surfaces. It is conceivable that electronegativity and chemical hardness may also be strongly related to the extent of adhesive interactions and shear rheology of solid oxides and hence to their lubricity. The new results have confirmed that electronegativity, like ionic potential, is indeed a valid quantum chemistry parameter that can be used in predicting the lubrication behavior of solid oxides. Generally, the higher the electronegativity of the solid oxides is, the lower the friction coefficients will be. However, chemical hardness did not yield a similar trend. In light of these new findings, we propose some guidelines for the formulation of novel oxide or alloy systems that can lead to the formation of lubricious oxides at elevated temperatures. The findings of this study may pave the way for designer-based tribosystems in general and smart tribochemical systems in particular in future tribological applications such as dry machining.

Application of the Extended Grunwald-Winstein Equation to Solvolyses of n-Propyl Chloroformate

Abstract: Application of the extended Grunwald-Winstein equation to solvolyses of n-propyl chloroformate in a variety of pure and binary solvents indicates an addition-elimination pathway in the majority of the solvents but an ionization pathway in the solvents of highest ionizing power and lowest nucleophilicity. For methanolysis, a solvent deuterium isotope effect of 2.17 is compatible with the incorporation of general-base catalysis into the substitution process. Activation parameters are consistent with the duality of mechanism. Very modest positive salt effects are observed on adding chloride or bromide salts to the ethanolysis.

Ab Initio Studies on the Preferred Site of Protonation in Cytisine in the Gas Phase and Water

Abstract: Ab initio calculations (HF, MP2, DFT for isolated and PCM for solvated molecules) were performed for cytisine ( 1 ) and its model compounds: N-methyl-2-pyridone ( 2 ) and piperidine ( 3 ). Among three heteroatomic functions (carbonyl oxygen, pyridone and piperidine nitrogens) considered as the possible sites of protonation in 1 , surprisingly the carbonyl oxygen takes preferentially the proton in the gas phase whereas in water the piperidine nitrogen is firstly protonated. For model compounds, the piperidine nitrogen in 3 is more basic than the carbonyl oxygen in 2 in both, the gas phase and water. Keywords: Cytisine; Site of protonation; Ab initio calculations; PCM; Gas phase and Solution Introduction Proton-transfer reactions play an important role in interactions of molecules with biological systems [1]. Biologically active molecules are usually polyfunctional derivatives in which the sites of protonation or deprotonation strongly depend on acid-base properties of individual functional groups, their intra- and intermolecular interactions and environment [2,3]. Examples are alkaloids, naturally synthesized by various plants, some of which have medicinal or poisonous properties [4]. Although,

Inductive QSAR Descriptors. Distinguishing Compounds with Antibacterial Activity by Artificial Neural Networks

Abstract: On the basis of the previous models of inductive and steric effects, ‘inductive’ electronegativity and molecular capacitance, a range of new ‘inductive’ QSAR descriptors has been derived. These molecular parameters are easily accessible from electronegativities and covalent radii of the constituent atoms and interatomic distances and can reflect a variety of aspects of intra- and intermolecular interactions. Using 34 ‘inductive’ QSAR descriptors alone we have been able to achieve 93% correct separation of compounds with- and without antibacterial activity (in the set of 657). The elaborated QSAR model based on the Artificial Neural Networks approach has been extensively validated and has confidently assigned antibacterial character to a number of trial antibiotics from the literature. Keywords: QSAR, antibiotics, descriptors, substituent effect, electronegativity. Introduction. Nowadays, rational drug design efforts widely rely on building extensive QSAR models which currently represent a substantial part of modern ‘

Synthesis and GIAO NMR Calculations for Some Novel 4-Heteroarylidenamino-4,5-dihydro-1H-1,2,4-triazol-5-one Derivatives: Comparison of Theoretical and Experimental 1Hand 13C- Chemical Shifts

Abstract: Department of Chemistry, Kafkas University, 36100 Kars, Turkey. *Author to whom correspondence should be addressed; e-mail: hyuksek98@yahoo.com Received: 7 April 2005 / Accepted: 21 August 2005 / Published: 25 August 2005 Abstract: 3-Alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones (1) reacted with 5-methylfuran-2-carboxyaldehyde to afford the corresponding 3-alkyl(aryl)-4-(5-methyl-2-furylmethylenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (2). Four newly synthesized compounds have been characterized by elemental analyses, IR,

Thermodynamics of Water-octanol and Water-cyclohexane Partitioning of some Aromatic Compounds

Abstract: The Gibbs free energy, enthalpy and entropy of partitioning of 45 simple aromatic compounds (phenols, benzoic acids and acetanilides) from water to octanol and from water to cyclohexane have been determined using the filter-probe method. This involved the measurement of partition coefficients over the temperature range 20-45oC. The aim of the work was to explore the effects of intramolecular hydrogen bonding and steric factors on the partitioning process. It was found that the intramolecular hydrogen bond is intact in 2-nitrophenol and salicylic acid, and possibly in 2-hydroxybenzaldehyde, in all three solvents, but 2-chlorophenol is intramolecularly hydrogen bonded only in inert solution. The evidence indicates that 2-nitroresorcinol and 2,6-dihydroxybenzoic acid possess only one intramolecular hydrogen bond, although they are theoretically capable of possessing two. There is evidence of steric shielding in 2,6-dimethylphenol, whilst 2,6-dimethylbenzoic acid and ortho-substituted acetanilides show evidence of steric twisting of the carboxyl and acetamido groups respectively out of the plane of the aromatic ring. Unusual steric effects are displayed in the methyl-2-nitrophenols whereby, depending upon the position of the methyl group, the intramolecular hydrogen bond is either weakened or strengthened.

Reduction of Sulfur Dioxide on Carbons Catalyzed by Salts

Abstract: . The reduction of SO 2 on different carbons in the presence of the nitrates and sulfides of sodium, potassium and calcium and potassium polysulfides was studied. The presence of salts increased the initial rate 2-5 fold for all of them and did not change the product distribution. The catalysis was not determined by the cation and there was no difference in the catalytic reactivity between nitrates and sulfides. The sulfur content of the activated carbon increased during the reaction on account of the stable reactive intermediates in the reduction of SO 2 . In the presence of NaNO 3 or Na 2 S, the amount of sulfur incorporated was in the molar ratio Na:S = 3 ± 0.3, and the XPS spectra of the residual carbon showed an increase of ca. 9% of the non-oxidized form of sulfur in the intermediates. In the absence of salt, it is proposed that after the adsorption of SO 2 on the carbon, a 1,3,2-dioxathiolane or 1,2-oxathietene 2-oxide are formed and that decompose to produce CO 2 and atomic sulfur. The non-oxidized sulfur intermediate would be an episulfide

How the Substituent Effect Influences π-Electron Delocalisation in the Ring of Reactants in the Reaction Defining the Hammett Substituent Constants σm and σp

Abstract: Application of the geometry (HOMA, EN, GEO) and magnetism based (NICS, NICS(1)) indices of aromaticity to optimised geometry of the ring in 12 meta – and 12 para – substituted benzoic acids and their anions by use of DFT computations at B3LYP/6-311+G(d,p) level has shown a very low substituent effect on the π-electron delocalisation. This resembles (qualitatively) the resistance of benzene (and typical aromatic systems) against reactions leading to the change of π-electron delocalisation.

13C-NMR Based Evaluation of the Electronic and Steric Interactions in Aromatic Amines

Abstract: Chemical shifts of the para carbon atoms, δ(13C-4), in a series of aromatic amines were used to calculate the σp, σR and σOR substituent constants for different amino groups. 1-Pyrrolidino, N,N-di-n-butylamino and N,N-diethylamino groups were found to be the most strong electron-donors. ortho-Substitution decreases the donor properties of the amino group. The amino groups in 2,6-di-i-propylaniline and N,N-2,6-tetramethylaniline have very weak electron-donor properties. The nitrogen atom in benzoquinuclidine and N,N-dimethyl-2,6-di-i-propylaniline have an electron-acceptor character. The calculated substituent constants of the amino groups studied are consistent with the spectral and reactivity data available in literature. Values of δ(15N) cannot be used as a direct measure of electronic effects of the N atom in anilines.

Acidity Study on 3-Substituted Pyridines

Abstract: A comprehensive theoretical study for the protonation of some 3-substituted pyridines has been carried out in aqueous solution (e=78.4) by semi empirical AM1 method in MOPAC2000 and PM5 method in MOPAC2002. Solvent effect was accounted for implicitly by means of the conductor like screening model (COSMO). The acidity constants of these pyridine derivatives have been calculated. The tautomeric and/or conformational equilibria for these compounds, where available, were also taken into account to find out the mol fractions of the species in aqueous media. The results obtained from the calculations were compared with the available experimental values, and the results indicate a considerable agreement with available experimental data.

Re-examination of Steric Substituent Constants by Molecular Mechanics

Abstract: Statistical analysis employing the set of the steric constants Ωj,k(Rc) is shown to be very effective in characterizing the substituent steric effect on organic reactions. Ωj,k(Rc) contains several variable parameters which are useful for the diagnosis of the character of steric effect. The parameters controlling the angular, or directional, weight (j,k) and the size of reaction center atom X(Rc) are varied in order to elucidate the characteristics of several steric substituent constants.

Facile Interfacial Electron Transfer of Hemoglobin

Abstract: We herein describe a method of depositing hemoglobin (Hb) and sulfonated polyaniline (SPAN) on GC electrodes that facilitate interfacial protein electron transfer. Well-defined, reproducible, chemically reversible peaks of Hb and SPAN can be obtained in our experiments. We also observed enhanced peroxidase activity of Hb in SPAN films. These results clearly showed that SPAN worked as molecular wires and effectively exchanged electrons between Hb and electrodes.Mediated by Conjugated Polymers

Substituent Effects in the 13C-NMR Spectra of Six-Membered Nitrogen Heteroaromatic Compounds

Abstract: It is shown that the 13C-NMR chemical shifts of carbon atoms in substituted sixmembered heteroaromatic compounds correlate with the correponding "additivity parameters" for substituted benzene derivatives. Thus, for precalculation of chemical shifts in such compounds, just one set of parameters can be used. The differences between experimental chemical shifts and those calculated from correlation with the common set may provide insights into intramolecular interactions not reported in the literature.

Study of Polymorph Prediction For L-Ascorbic Acid

Abstract: Highly Filled Materials Institute (HFMI), Stevens Institute of Technology, Hoboken, New Jersey 07030, USA * Author to whom correspondence should be addressed; Department of Chemistry, Kafkas University, Kars, Turkey, TR 36100. E-mail: arsla33@hotmail.com Received: 31 October 2005 / Accepted: 29 November 2005 / Published: 06 December 2005 Abstract : Possible polymorphs of L-ascorbic acid were investigated, considering eight space groups and assuming one molecule in the asymmetric unit. The grid-search method was compared with a Monte Carlo approach as performed in the Biosym / MSI polymorph Predictor. A number of possible crystal structures were found, including the experimental structure. Energy minimizations were performed with a united-atom force field. In all cases, the experimental structure had a low lattice energy. The number of hypothetical crystal structures was reduced considerably by removing space-group symmetry constraints, or by a primitive molecular dynamic shake-up. Nevertheless, sufficient structures of equal or lower energy compared with the experimental structure remained to suggest that other factors need to be considered for polymorph predictions of materials. Keywords : Polymorph predictor; Crystal structure prediction, L-Ascorbic Acid 1. Introduction The relationship between the crystal morphology and the internal arrangement of atoms in the crystal is of great interest to chemists and chemical and process engineers. If the drug can crystallize in two or more polymorphs with different bioavailabilities, the optimal dose depends on the polymorph used in the formulation. The polymorphic behavior of organic and inorganic solids can be of crucial importance in the pharmaceutical industry [1]. Properties varying between polymorphs include stability (i.e., shelf life of drug), crystal shape, compressibility, density (important in formulation), and the

Octopamine Levels in Blattella Germanica L. Tissues by Capillary Gas Chromatography with Electron Capture Detection

Abstract: Distribution and levels of octopamine (OA), one of the biogenic amines in the invertebrate nervous system, may have significant effects on insect physiological processes including growth, feeding and reproduction. In this paper capillary gas chromatography with electron capture detection (GC-ECD) and mass selective detection (GC-MS) were used to determine the content of OA in Blattella germanica L. central nervous system (CNS), and that of OA in cockroach stressed by kinds of insecticides, known octopaminergic agonists and some essential oils. A derivatization method for organic extracts via reaction with pentafluoropropionic anhydride (PFPA) was developed. The resulting OA derivatives were confirmed by GC-MS to be tris-pentafluoropropionyl-OA. The method was used to quantify the amount of OA in insect issues by capillary GC-ECD through an extraction-derivatization-liquid/liquid partition procedure. Average OA content in normal cockroaches was determined to be 68.49 ± 7.31 ng/g tissue (N=5 determinations). It was shown that insecticides including chlordimeform, methomyl, permethrin, chlorfluazuron, malathion, trichlorfon and some oxazolidine agonists, essential oils including eugenol, cinnamic alcohol, phenyl ethyl alcohol could led to significant increase of OA levels in the cockroach CNS comparing with which in insect treated by 1-butanone. Malathion, trichlorfon, chlorfluazuron and cinnamic alcohol were shown to be able to cause a 20- fold increase in OA levels.

Ab initio post-HF CCSD(T) Calculations for Triplet and Singlet Methylene in Four consecutive Dunning Basis Sets with Extrapolations to Infinite Limits for Various Molecular Properties

Abstract: Stationary points for four geometrically different states of methylene: bent and linear triplet methylene, bent and linear singlet methylene were investigated using the highly reliable post-HF CCSD(T) method. Extrapolations to the CCSD(T) basis set (CBS) limit from Dunning triple to quintuple correlation consistent polarized basis sets were performed for total energies, for the equilibrium CH distances re(CH), for singlettriplet separation energies, for energy barriers to linearity and for correlation energies. Post-HF calculations with Dunning basis sets of the literature are presented for comparisons.

Study on the XPS-ESCA of Aluminum Phosphide Products

Abstract: XPS-ESCA analysis showed small signal for phosphorus in fresh specimens of aluminum phosphide (AlP). After removal of a layer of about 0.5 – 1.0 μm by argon ion sputtering, it was observed that signal intensities from oxygen and aluminum increased. The oxygen signal decreased as a function of sputtering time, synchronously with the increase of the phosphorous signal from the AlP nucleus. The aluminum signal, which was considered to be mainly due to AlP and Al(OH)3, remained constant. Other impurity elements including N, Mg, etc., were identified in the technical 85% AlP and AlP tablet formulated products.

Jubilite: A 4-,8-connected Cubic Structural Pattern in Space Group Pm3

Abstract: In the course of investigating structural modifications of the 3-,4-connected net known as the Pt3O4 structure-type (waserite), a novel 4-,8-connected structure-type was discovered. This lattice is generated by replacing the 3-connected trigonal planar vertices of the Pt3O4 structure-type with 4-connected tetrahedral vertices, to achieve a structure which possesses a generic empirical formula of JK6L8. In such a topological modification, the four 3-fold axes of the parent cubic, Pm3n, Pt3O4 structure-type are retained. Thus the 4-connected tetrahedral vertices are oriented so as to preserve cubic symmetry in the resulting Pm3, JK6L8 (jubilite) lattice. The unit cell contains a single 8-connected cubecentered vertex, six 4-connected distorted square planar vertices and eight 4-connected distorted tetrahedral vertices. It is a Wellsean structure with a Wells point symbol given by (4166484)(4282)6(4383)8 and a Schlafli symbol of (53/4, 4.2667). This latter index reveals a decrease in the lattice’s polygonality and concomitant increase in the connectivity through the transformation from waserite to jubilite. The topology of the parent waserite lattice (Pt3O4) corresponds to that of the Catalan structures with the Wells point symbol (84)3(83)4, which has the Schlafli symbol (8, 3.4285). Finally, it can be seen that a sequence of structure-types starting with waserite (Pt3O4) and moving to jubilite (JK6L8) and finally to fluorite (CaF2) represents a continuous crystallographic structural transformation in which the symmetry and topology undergo concomitant changes from one structure-type (waserite) to the other structure-types. The topology of the fluorite lattice, represented by the Wells point symbol (424)(46)2, and the Schlafli symbol (4, 51/3), indicates a discontinuous topological transformation from the intermediate jubilite lattice; like the discontinuous topological transformation from Pt3O4 to JK6L8; in which the polygonality is again reduced, in this step from 53/4 to 4, and the connectivity is concomitantly increased, from 4.2667 to 51/3, during the continuous structural transformation. The l index, a topological measure of the form of a structure-type in terms of the ratio of the weighted average polygonality to the weighted average connectivity in the unit cell, decreases in the sequence from Pt3O4 (2.3333) to jubilite (1.3476) to fluorite (0.7500). This indicates the discontinuous, though monotonic, appearance of more closed networks upon increasing the connectivity and concomitantly decreasing the polygonality in the structural sequence. Interestingly, the ratios of the form indexes of the adjacent members in this series: lwaserite/ljubilite and ljubilite/lfluorite, are approximately equal to each other.

Inhibition of Heme Peroxidase During Phenol Derivatives Oxidation. Possible Molecular Cloaking of the Active Center

Abstract: Institute of Biochemistry, Mokslininku 12, 08662 Vilnius, Lithuania * Author to whom correspondence should be addressed; E-mail: a3arzi@vaidila.vdu.lt Received: 1 March 2005 / Accepted: 29 August 2005 / Published: 20 October 2005 Abstract: Ab initio quantum chemical calculations have been applied to the study of the molecular structure of phenol derivatives and oligomers produced during peroxidase-catalyzed oxidation. The interaction of substrates and oligomers with Arthromyces ramosus peroxidase was analyzed by docking methods. The most possible interaction site of oligomers is an active center of the peroxidase. The complexation energy increases with increasing oligomer length. However, the complexed oligomers do not form a precise (for the reaction) hydrogen bonding network in the active center of the enzyme. It seems likely that strong but non productive docking of the oligomers determines peroxidase inhibition during the reaction. Keywords: Ab initio , docking, peroxidase, phenol, oligomer Introduction Enzymatic oxidation of phenol substances has attracted considerable attention recently due to environmental effects and polymer synthesis [1,2]. The environmental effects are associated with large scale production and use of man-made phenol substances at concentrations that cause ecologically undesirable effects. Many of these compounds are highly resistant to biotic and abiotic degradation and, as a result, remain in the environment at toxic levels. Enzyme-catalyzed degradation of phenol substances has been considered as one of possibilities for detoxification of these congeners [1].

Influence of Long-Tailed Alcohols on the Solubilisation of Cationic DHAB Bilayers

Abstract: The effects of n-decanol and cetyl alcohol incorporated into cationic di-n-hexadecyldimethylammonium bromide (DHAB) bilayers on the packing and the resistance against solubilisation by Triton X-100 have been investigated. Solubilisation experiments revealed that the mismatch between the C10-tail of n-decanol with the DHAB-tails does not affect the structural integrity of the vesicles. On the contrary, upon increasing amounts of cetyl alcohol, of which the tail matches in size with the DHAB-tails, breakdown of the vesicles is promoted, whereas complete solubilisation is strongly hampered. The system is further investigated by DSC and cryo-EM experiments. In addition, the effects of n-decanol and cetyl alcohol embedded into DHAB bilayers on the vesicular rate constants for the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) suggest that both alcohols affect the structure of the Stern region in an equal manner, leading to a decrease in the catalysis. Therefore, it is concluded that addition of the alcohols leads to changes in properties of the interior of the bilayer, rather than the polar-apolar interface.

Structural Stability and Vibrational Analyses of Haloselenonyl Azides, XSeO2-NNN, where X is F, Cl, Br

Abstract: Wolfgang Fo rner*, Hassan M. Badawi, and Zaki S. Seddigi Department of Chemistry, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia *Author to whom correspondence should be addressed; e-mail: forner@kfupm.edu.sa Received: 7 March 2005 / Accepted: 27 March 2005 / Published: 4 October 2005 Abstract: The structural stability of haloselenonyl azides was investigated by quantum mechanical Moller-Plesset perturbation theory of second order and density functional theory calculations. The 6-311+G** basis set was used to include polarization and diffuse functions in the calculations at the DFT-B3LYP level. The potential scans for the rotation of the -NNN rotor were calculated and found to be consistent with a single minimum that corresponds to a gauche conformation (-NNN moiety nearly eclipses one of the two selenonyl Se=O bonds) for the three halogens at ambient temperature. The structural parameters for the minima calculated by MP2 and DFT turned out to be very similar. The vibrational modes, infrared and Raman intensities as well as depolarization ratios were calculated at DFT-B3LYP/6-311+G** level for the three molecules in their gauche conformations. The potential energy distributions among symmetry coordinates of the normal modes of the mo-lecules in their gauche conformation were then computed from normal coordinate analyses. Keywords: MP2 and DFT calculations; structural stability; vibrational modes and assign-ments; haloselenonyl azides. Introduction The conformational behavior of fluorosulfonyl isocyanate F-SO

Kinetics and Mechanism of Acetoxymercuration and Acid- Catalysed Hydration of α-Alkylstyrenes

Abstract: Nine α-alkylstyrenes carrying the following substituents have been synthesised: methyl, ethyl, propyl, butyl, pentyl, iso butyl, iso propyl, sec -butyl and tert -butyl. Kinetics has been measured for the reaction of these compounds with mercuric acetate in anhydrous acetic acid at 25 °C. The rate constants are very sensitive to inductive effects (ρ I = –49.5 in AISE theory) and steric effects (ψ = –1.59 according to Charton). These results support the presumed existence of an intermediate with an asymmetrically bound acetylmercuric cation to carbon atoms of the vinyl group of styrene. The kinetics of an acid-catalysed hydration of the above-mentioned α-alkylstyrenes were also measured in aqueous sulphuric acid at 25 °C. The derivatives exhibited kinetically a consecutive isomerisation reaction giving the more stable substituted styrenes. The values of the slope m ‡ m * of the dependence upon the excess acidity function ( X ) were evaluated, and exceptionally low values were found for the butyl and pentyl substituents (1.02 and 0.73, respectively), while on the other hand

Special Issue Dedicated to Professor Marvin Charton – Correlation Analyst Par Excellence

Abstract: The collection of papers dedicated to Marvin Charton that we present in this special issue of IJMS covers a variety of fields of scientific research and well represents his wide range of interests – all the contributors are his friends or users of his ideas and the results of his scientific work and have often also been partners in subtle and very fruitful discussions with Marvin.[...]

Tetra-tert-Butyl-di-m-Hydroxo Digallium(III) and 1,12-Diaza-3,4:9,10-Dibenzo-5,8-Dioxo-cyclo-Pentadecane. Structure and Isomers of the Coordination Compound

Abstract: Tri-t-butylgallium has been reacted with the macrocycle 1,12-diaza-3,4:9,10-dibenzo-5,8-dioxocyclopentadecane which could be a potential ligand for gallium(III). A reaction product was analyzed and single crystal X-ray diffraction experiments showed that it consisted of the cyclic dimer of di-t-butylgallium-hydroxide hydrogen bonded to the macrocycle. Without a co-crystallized organic molecule di-t-butylgallium hydroxide crystallizes as a trimer. Density functional calculations have been used to predict the structures and the total energies for the monomer, dimer, trimer, and tetramer of dimethylgallium hydroxide in order to provide a basis for the understanding of oligomer population for the dimethylgallium hydroxides. Force field calculations are shown to be able to produce a similar strain energy difference for dimer, trimer, and tetramer forms of (CH3)2Ga(OH) and this method can economically be used for larger alkyl groups. The force field computations show that the trimeric di-t-butyl gallium(III) hydroxide is much more stable than the dimeric form which therefore must owe its existence to the association with the hydrogen-bonded macrocycle.

Solvent and Ligand Effects on the Tandem Addition-Lithiation-Electrophilic Substitution of Phenyllithium on α,β-Unsaturated Carbonyl Compounds

Abstract: The reaction of phenyllithium with E-cinnamaldehyde is extremely sensitive to the reaction conditions and surprising changes in the product distribution were observed upon changes in the solvent, concentrations, duration or temperature of the reaction. For these reasons the above mentioned reaction was considered an appropriate model to examine solvent and aggregation effects of PhLi. On the other hand, when two or trhee equiv of phenyllithium are used, instead of one, the reaction transforms into a surprising tandem addition-lithiation-β-alkylation sequence, that can be successfully applied to the synthesis of substituted dihydrochalcones. The observed effects upon changes in the reaction conditions, as well as the effects of additives that modify the PhLi dimer-monomer equilibrium are consistent with a reaction pathway in which dimeric phenyl lithium attacks to the E-cinnamaldehyde without previous deaggregation. Usually, monomers are found to be more reactive than dimers, but, in this reaction the opposite effect is observed, and the tandem reaction spectacularly decreases with the (PhLi)2 concentration.

Marvin Charton - Correlation Analyst Par Excellence

Abstract: Since the late 1950s Marvin Charton, physical organic chemist, of Pratt Institute, Brooklyn, New York has studied structure-property relationships through correlation analysis, and has become one of the leading authorities in this field.