bluuebunny/crossref_metadata_2025 huggingface dataset:
The Reaction of Psoralens and Related Benzofurans with Singlet Oxygen An Account of Current Research
Authors: Berdahl Donald R. , Wasserman Harry H.
Published: November 2013

Recent work dealing with the role of singlet oxygen in the biological activity of the psoralens has been reviewed. The reaction of singlet oxygen with benzofurans gives products which result from initially formed dioxetanes. Evidence for dioxetane intermediates was obtained from experiments using diphenyl sulfide as a trapping agent. Psoralen derivatives which contain alkyl or aryl groups on the furan double bond react readily with singlet oxygen to give dioxetane cleavage‐type products. Psoralens which lack furan substituents but possess powerful electrondonating groups in the 5‐ and 8‐positions give rise to peroxidic intermediates which are stable only at low temperature.
Cosensitized Electron‐Transfer Photooxygenation of Epoxides. A New Synthesis of Ozonides
Authors: Schaap A. Paul , Siddiqui Shahabuddin , Balakrishnan P. , Lopez Luigi , Gagnon Steven D.
Published: November 2013

9,10‐Dicyanoanthracene (DCA) and biphenyl (BP) cosensitize the electron‐transfer photooxygenation of epoxides in oxygen‐saturated acetonitrile to form ozonides. These epoxides do not measurably quench the fluorescence of DCA and are, therefore, relatively unreactive under standard photooxygenation conditions with only DCA as sensitizer. However, a dramatic increase in the rate of reaction is observed upon the addition of BP as a non‐light‐absorbing cosensitizer. An investigation of the stereochemistry of the reaction with cis‐ and trans‐2,3‐diphenyloxiranes has shown that both epoxides are converted exclusively to the cis‐ozonide. This striking stereochemical result is consistent with a proposed mechanism involving singlet oxygen addition to an intermediate carbonyl ylide.
Activation of Superoxide Ion by Reactions with Protons, Electrophiles, Secondary Amines, Radicals, and Reduced Metal· Ions
Authors: Roberts Julian L. , Sawyer Donald T.
Published: November 2013

In aprotic and aqueous media the proton‐induced disproportionation of superoxide ion (O−2) yields a variety of reactive species (HO2·, H2O2, HO−2, and · OH). In aprotic media O−2 rapidly degrades polychlorinated hydrocarbons (CCl4, HCCl3, and DDT) to oxygenated products (CCl4 →Cl3COO·; HCCl3→ Cl2C: and Cl2C=O). Alkyl halides react more slowly (BuCl →BuOO· and BuOO−). Formation of O−2 in the presence of methyl viologen (MV2+), reduced flavins, esters, and low‐valent transition metal complexes results in the formation of reactive oxygenating agents and reaction mimics for oxygenases [MV+‐OO‐, 4a‐hydroperoxyflavins, RC(O)OO−, and Zn11(O2 ·)+]. Kinetic data for the proton‐induced disproportionation of O−2 in water and the nucleophilic reactions of O−2 in aprotic solvents lead to the conclusion that the latter are probably of little significance for biological oxygenation reactions.
The Radiation Chemistry of Cytochrome c
Authors: Koppenol W. H. , Butler J.
Published: November 2013

The literature on the reaction of cytochrome c with the radiolytically generated radicals \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm e}_{{\rm eq}}^ -,^. {\rm OH,}^{\rm .} {\rm H,CO}_2^ -,{\rm O}_{\rm 2}^ -,{\rm Br}_{\rm 2}^ - $\end{document} and various organic radicals is reviewed. It would appear that negatively charged radicals, aided by the electric field of cytochrome c, react at the exposed haem edge. Uncharged organic radicals also react at this site. \documentclass{article}\pagestyle{empty}\begin{document}$ ^. {\rm H} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ ^. {\rm OH} $\end{document} are likely to reduce the prosthetic group indirectly by a tunnelling mechanism.
On the Use of OH · Scavengers in Biological Systems
Authors: Czapski Gidon
Published: November 2013

The problem of using OH scavengers, with special emphasis on biological systems, is discussed. The problems arising from inhomogeneity and from possible large gradients in scavenger concentrations between the cell and media, or between different parts of the cell, are analysed, and their implications on scavenging efficiency are examined. The possible reactions of secondary radicals and their effect on scavenging and even on possible sensitization are described. The limitations of the usage of OH scavengers in biological systems are discussed.
Nickel‐Catalyzed Addition of Methylmagnesium Bromide to Alkynylsilanes. Stereospecific Synthesis of Tetrasubstituted Alkenes
Authors: Conn Robin S. E. , Karras Michael , Snider Barry B.
Published: November 2013

Methylmagnesium bromide adds to trimethylsilyloctyne (1) in the presence of 10 mol% 1:0.67 nickel acetylacetonate‐trimethylaluminum to give a 9:1 mixture of alkenyl Grignard reagents 2a and 3a. This mixture reacts with water, deuterium oxide, formaldehyde, acetaldehyde, carbon dioxide, iodine, vinyl bromide or allyl bromide to give the expected products 2, 3b to 2, 3j. Nickel catalyzed carbometallation of 4 with MeMgBr followed by quenching with formaldehyde and desilylation gives trans, trans‐farnesol (5c). Nickel catalyzed addition of MeMgBr to 6a and 6b proceeds analogously, except that initially formed alkenyl Grignard reagents 7a and 7b isomerize completely to 8a and 8b which are stabilized by chelation. This carbometallation reaction allows the synthesis of both isomers of an allylic alcohol, such as 12 and 13, from a common intermediate 2a.
Catalytically Reactive Ruthenium Intermediates in the Homogeneous Oxidation of Alcohols to Esters
Authors: Blum Yigal , Shvo Youval
Published: November 2013

Ru(η4‐tetracyclone)(CO)3 and [Ru(η4‐tetracyclone)(CO)2]2 were prepared from Ru3(CO)12 and diphenylacetylene. Their rate of oxidation of PhCH2OH are, respectively, 1.6 and 4.2 times faster than their precursor Ru3(CO)12. Both complexes, as well as others, were also found in the oxidation reaction mixture: PhCH2OH+ Ph2C2 + Ru3(CO)12 which generates benzyl benzoate. Ru(η4‐tetracyclone)(CO)2 is most probably the true catalytic species in the catalytic oxidation of alcohols to esters.
Infrared Multiphoton Absorption by Methanol
Authors: Evans D. K. , Mcalpine Robert D. , Adams H. M.
Published: November 2013

The multiphoton absorption of CO2 laser 9 μm P(18), P(20) and P(34) lines by methanol has been studied for fluences from 10−3 to ∼ 20 J/cm2, pulse widths of 6 and 60 ns FWHM and methanol pressures from 0.067 to 13.3 kPa. The absorption depends on laser fluence, laser line and gas pressure but not on laser beam intensity. For each line studied the results can be expressed as a function of fluence and the product of pressure with pulse width. Absorption by a Q‐branch transition (9P(34) pumping) shows a faster relaxation and a stronger absorption than R‐branch transitions (9P(18) and 9P(20) pumping). The results obtained here are compared to multiphoton absorption data for an HF laser pumping the OH stretch vibration.
Nonlinear Multi‐Photon Excitation and Dissociation in Intense Laser Fields: Recent Developments in Floquet Theory and Quasi‐Energy Methods
Authors: Chu Shih‐I , Ho Tak‐San
Published: November 2013

A short account of several recent developments in semiclassical Floquet theory and quasi‐energy (QE) methods for nonperturbative treatments of intense field multiphoton excitation (MPE) and dissociation (MPD) processes is given. Topics discussed include (a) non‐Hermitian Floquet theory and complex QE method for MPD, (b) MPE quantum dynamics in intense laser and static electric fields, (c) nonadiabatic approach for resonant infrared (IR) multiphoton absorption spectroscopy, (d) IR MPE/MPD of triatomic molecules — most probable path approach, and (e) many‐mode Floquet theory. Also presented are new methods and results for nonlinear MPE of finite level systems in linearly and circularly polarized bichromatic fields.
Stepwise Excitation Processes in Photodissociation and Detection
Authors: Reisler H. , Radhakrishnan G. , Sumida D. , Pfab J. , Chou J. S. , Nadler I. , Wittig C.
Published: November 2013

Two‐photon processes in which stationary intermediates are involved in the excitation are discussed, and three processes are described in detail: (a) stepwise 2‐photon laser induced dissociation of NCNO at wavelengths 600–800 nm, followed by detection of the CN fragment via laser induced fluorescence (LIF); (b) detection of HONO via a 2‐frequency scheme, in which dissociation is induced at 355 nm and is followed by LIF detection of the OH fragment; (c) stepwise 2‐frequency 2‐photon ionization detection of nascent PO produced via the collision free IR photolysis of aliphatic phosphonates and phosphites. Absorption throughout the B2Σ+‐X2 system of PO is followed by ionization using 266 nm radiation.
An Artificial Channel Type Ionophore
Authors: Nolte R. J. M. , van Beijnen A. J. M. , Neevel J. G. , Zwikker J. W. , Verkley A. J. , Drenth W.
Published: November 2013

A polymer of an isocyanide (R–N=C<)n has been synthesized in which R contains a benzo‐18‐crown‐6 group. The crown ether rings are on top of each other and form channels which bind metal ions. The channel compound can be incorporated in vesicles and is able to transport ions across the bilayer membrane.
Conformational Versatility of Open‐Chain Polyethers: Crystal and Molecular Structures of the Ba(SCN)2 Complexes of Two Heptaethyleneglycol Diaryl Ethers
Authors: Hilgenfeld R. , Hirayama F. , Bhagwat V. , Saenger W. , Weber G. , Sheldrick G. M. , Sieger H. , Vögtle F.
Published: November 2013

The crystal structures of the Ba(SCN)2 complexes of two linear octaethers, heptaethyleneglycol diphenylether (HGPE; 1,20‐bis(phenyloxy)‐3,6,9,12,15,18‐hexaoxaicosane) and heptaethyleneglycol dinaphthylether (HGNE; 1,20‐bis(naphthyloxy)‐3,6,9,12,15,18‐hexaoxaicosane), are reported. In spite of their close similarity, the ligands adopt quite different conformations in their Ba(SCN)2 complexes. HGPE wraps around the metal ion in a discontinuous helix providing seven of its eight ether oxygens for coordination. 10‐fold coordination of Ba2+ is completed by the nitrogens of the SCN− ions and by a water molecule for which an occupancy of 0.37(5) was determined. In contrast, HGNE behaves as a hexadentate only. The barium ion is 9‐fold coordinated to six ether oxygens, to a water molecule, to one SCN− ion via its nitrogen atom and to a symmetry‐related thiocyanate ion via its sulphur atom. The second SCN− ion does not contact the metal ion but is hydrogen‐bonded to two symmetry‐generated water molecules. HGNE displays some unusual conformational features never found before for open‐chain polyethers.
Stoichiometry and Structure of the Complexes Between Lanthanide Ions and Macrocyclic Crown Ethers Containing from Four to Seven Coordinating Sites
Authors: Bünzli J.‐C. G. , Wessner D.
Published: November 2013

The factors influencing the stoichiometry and the structure of the complexes between trivalent lanthanide perchlorates, hexafluorophosphates, nitrates, trifluoroacetates, chlorides, bromides, isothiocyanates and the polyethers 12‐crown‐4, 15‐crown‐5, 18‐crown‐6, dibenzo‐18‐crown‐6 and 21‐crown‐7 are reviewed. The properties of divalent lanthanide and Ce(IV) complexes with crown ethers are presented and discussed.
Cation Transport at 25°C from Binary Cd2+–Mn+ Mixtures in a H2O‐CHCl3–H2O Liquid Membrane System Containing a Series of Macrocyclic Carriers[1]
Authors: Izatt Reed M. , Izatt Steven R. , Mcbride Don W. , Bradshaw Jerald S. , Christensen James J.
Published: November 2013

Macrocycle‐mediated fluxes of Cd(NO3)2 and of several binary mixtures of Cd(NO3)2 with the nitrate salt of either Na+, K+, Rb+ Cs+, Ag+, Ca2+, Sr2+, Pb2+, Zn2+, or Cu2+ have been determined in a H2O‐CHCl3–H2O liquid membrane system. Of the macrocycles studied, 2.2 and 2.2DD most successfully transported Cd2+ In the Cd2+–Mn+ mixtures, Cd2+ was transported selectively with 2.2 when Mn+ was either an alkali or an alkaline earth cation. However, when Mn+ was either Ag+, Pb2+, or Cu2+ the Cd2+ flux was reduced sharply. Generally, cation flux was greater for 2.2DD than for 2.2 with selectivity for Cd2+ being altered also in several cases. Relative fluxes from binary cation mixtures depend on metal cation radius, macrocycle cavity diameter, ligand ring substituent and log K for metal ion‐macrocycle interaction.
Structures of the (4S, 14S)‐4, 14‐Dimethyl‐3,6,9,12,15‐pentaoxa‐21‐azabicyclo[15.3.1] heneicosa‐1(21) 17,19‐Triene‐2,16‐dione Complexes of R‐and S‐α‐(1‐Naphthyl)ethylammonium Perchlorate
Authors: Davidson Richard B. , Kent Dalley N. , Izatt Reed M. , Bradshaw Jerald S. , Campana Charles F.
Published: November 2013

Crystal data for the more stable (R) and less stable (S) 1:1 macrocycle‐cation complexes are as follows: R cation: Mr = 625.08, orthorhombic P212121, a = 8.47(1), b = 11.78(1), c = 31.19(6) A, V = 3112.0(123) Å3, Z = 4, Dx = 1.333 kg m−3, λ(Mo Kα) = 0.71073 μ = 1.90 cm−1, F(000) = 1320, T = 295 K, R = 0.17 for 1680 reflections. S Cation: Mr = 625.08, monoclinic, P21, a = 8.654(2), b = 11.954(3), c = 15.130(4) Å, β = 97.39(2)°, V = 1552.2(12) Å3, Z = 2, Dx = 1.337 kg m−3, λ(Mo Kα) = 0.71073, μ = 1.91 cm−1, F(000) = 660, T = 295K, R = 0.081 for 2751 unique reflections. Crystals of the complexes were prepared by the authors. The greater thermodynamic stability of the R cation complex is consistent with the observation that this cation experiences less steric interaction with the methyl substituent of the ligand than does the S cation.
Protonation of Macrocyclic Polyethers
Authors: Jagur‐Grodzinski Joseph
Published: November 2013

Proton affinity of various “crown” ethers is discussed. Equations are given for simultaneous calculation of the complexation and the dissociation constants from conductivity data. pKf in 1.2‐dichloroethane is 8.6 and 8.3, respectively, for the cis‐syn‐cis and the cis‐anti‐cis isomers of dicyclohexyl‐18‐CR‐6, the most basic among the investigated “crown” ethers. pKf = 8.2 for the mixture of these isomers in acetonitrile (AN). The effect of water on pKf of “crown” ethers in aprotic solvents is discussed. It is suggested that a monohydrate of the “oxonium‐crown” rather than a “hydronium‐crown” may be formed. The proton binding capacity of “crown” ethers may be applied for extraction of acids and in catalysis. Dicyclohexyl‐24‐CR‐8 has been found to be an equally effective extractant for HNO3 as the Dicyclohexyl‐18‐CR‐6.
Ring Size Effect on the Chemical Properties of Monovalent Nickel Complexes with Tetraazamacrocyclic Ligands in Aqueous Solutions
Authors: Jubran Nusrallah , Cohen Haim , Meyerstein Dan
Published: November 2013

The chemical properties of the monovalent nickel complexes, NiLi+, where L1 = 1,4,7,10 tetraazacyclotridecane and L3 = 1,4,8,12 tetraazacyclopentadecane, in aqueous solutions were studied electrochemically and pulse‐radiolytically. The results are compared with those for L2 = 1,4,8,11 tetraazacyclotetradecane which were earlier reported. The redox potentials for the NiLi2+/NiLi+ couples are < −1.70, −1.56 and −1.50 V vs. Ag/AgCl for L1, L2 and L3 respectively. NiL+2 has the longest half‐life in neutral solutions, ca 2 s and NiL1 the shortest ca 100 μs. NiL+1 and NiL+2 react with N2O to yield NiLi3+ in fast reactions; this reaction cannot be studied for NiL+3. CO−2 radicals reduce NiL2+1 and NiL2+2 in a reaction approaching the diffusion controlled limit via the bridged mechanism. No reaction between CO−2 and NiL3(H2O)2+2 is observed.
Reactions of Trivalent Silver with One‐Electron Reducing Agents
Authors: Kirschenbaum Louis J. , Borish Edward T. , Rush James D.
Published: November 2013

Kinetic and stoichiometric data are reported for the reduction of Ag(OH)−4 with Fe(CN)4−6, MnO2−4 and Mo(CN)4−8. The rate constants for reduction to Ag(II) are 1.1 × 105 M−1 s−1, 1.3 × 104 M−1 s−1 and < 1 × 102 M−1 s−1, respectively, at 25°C and μ = 1.2 M. Reaction with Mo(CN)4−8 results in an apparent one‐electron equilibrium, indicating a Ag(OH)−4/[Ag(II)]n potential near that of the Mo(V)/MO(IV) couple. In the Fe(CN)4−6 and MnO2−4 reactions, there is a competition between transfer of a second electron to silver and polymerization of silver(II). A general mechanism for these reactions is presented.
Stability Constants of Oximes of 4‐Substituted‐2‐acetylphenols [1]
Authors: Shai Y. , Warshawsky A.
Published: November 2013

Proton‐ligand stability constants (pKd) and metal‐ligand stability constants for six oximes of 4‐substituted‐2‐acetyl phenol in H2O: Dioxane (1:3) are obtained by the spectrophotometric method of Magnusson et al. as modified by Patel et al.
A Mechanistic Aspect of the Remote Asymmetric Transmission Observed During Substrate Reduction with Chiral NADH Model Compounds
Authors: Baba Naomichi , Hoshide Fumitoshi , Oda Jun'Ichi , Inouye Yuzo
Published: November 2013

Asymmetric reduction of ethyl benzoylformate were conducted using chiral NADH model compounds with various substituents at the 3‐ and N1‐positions of the dihydronicotinamide. In one case, in which l‐prolinamide resides at the terminal of the N1‐substituent, the optical yield was 90%; the remote asymmetric induction was ascribed to a stereospecific blockage of one of the diastereotopic faces in the dihydronicotinamide by an interaction of the amide functions with magnesium.
Anion Exchange Kinetics in Resins of High Selectivity. Part II. The Case of Chloride/Sulphate Exchange
Authors: Helfferich F. G. , Liberti L. , Petruzzelli D. , Passino R.
Published: November 2013

Five kinetic models potentially applicable to ion exchange with ions of high selectivity, discussed in Part I of this study, are systematically applied to experimental data on chloride/sulfate forward and reverse exchange and sulfate isotopic exchange with three different types of resins (quaternary ammonium, tertiary amine, and secondary amine groups) and highly dilute solutions (< 0.006 N). Interpretation of these data shows conceivably that the system is controlled by film diffusion, with a small contribution from intraparticle diffusion in forward and isotopic exchange and especially for the resin of highest sulfate selectivity.
Selective Potentiometric Gas‐Sensing Membrane Electrodes
Authors: Rechnitz G.A.
Published: November 2013

Potentiometric gas‐sensing membrane electrodes have been investigated for both the CO2 and NH3 systems from the point of view of selectivity and dynamic response. Selectivity is found to be primarily determined by the acid‐base properties, not the volatility, of the interferents. The dynamic response characteristics, on the other hand, are a function of the internal electrolyte layer and the osmolarity of the sample solution.
Transition Metal‐Chelating Phase Transfer Agents from 3,4‐Disubstituted Benzylhalides
Authors: Warshawsky Abraham , Deshe Abraham , Shai Yehiel
Published: November 2013

A unified approach to the synthesis of chelating phase transfer agents which uses attachment of various side‐chains to a single chelating molecular precursor (such as 2‐acetyl‐4‐chloromethyl phenol, 4‐chloromethyl salicylaldehyde, 5‐chloromethyl‐8‐hydroxyquinoline), by alkylation at carbon (on aromatic substrates), at oxygen (on alkanols, oligoethylene glycols) or at nitrogen (dialkylamines), is presented. The reaction of a model precursor, 2‐acetyl‐4‐chloromethyl phenol, is studied in detail. The proton–ligand and proton–metal stability constants and Cu(II) phase transfer properties is determined.
Uranium Recovery from Phosphoric Acid with Selective Resins
Authors: Belfer Sofia , Korngold Emmanuel
Published: November 2013

The synthesis and performance of resins selective for adsorbing uranium from wet‐process phosphoric acid were studied. The resins' capacity for uranium was determined in batch experiments and in columns. The morphology of the resin was examined by scanning electron microscopy. The conditions of column loading and elution were found and the concentration of uranium in the eluent was increased more than 50‐fold from 0.15 g/l to 5–7.
Synthesis and Cycloaromatization of Allenyl Ethynyl Sulfides and Selenides [1]
Authors: Braverman Samuel , Duar Ytzhak , Freund Meir
Published: November 2013

γ,γ‐Dimethylallenyl 1‐alkynyl sulfides 8a–d have been prepared by reaction of the corresponding alkynyllithium with γ,γ‐dimethylallenyl thiocyanate while the selenide analogs 10a,b have been obtained by an SN2′ reaction of the appropriate alkynyl selenide with α,α‐dimethylpropargyl bromide. Sulfides 8a–d display a high thermal reactivity, undergoing cyclization to the corresponding thiophenic derivatives 11a–d, together with thiophenic dimers such as 12–15, and some polymerization, under certain conditions. In contrast, selenides 10a,b are generally unreactive. The reaction exhibits a remarkable solvent effect. In isopropanol, only monomeric products are observed and the yield is greatly improved. An intramolecular free radical mechanism, involving the diradical intermediate 19, is suggested on the basis of the observed dimerization, solvent effect, deuterium labeling and a kinetic study of the reaction. The differences in reactivities between the analogous sulfides 8 and selenides 10 can be attributed to the varying ability of the respective heteroatom to stabilize the vinyl radical intermediate.
Optical Activity of Nascent Twisted Allene and its Induction by Circularly Polarized Light
Authors: Chiu Ying‐Nan
Published: November 2013

The evolution of optically active twisted allene (D2 symmetry) from orthogonal (D2d) and planar (D2h) structures is traced by construction of “chiral” molecular orbitals as a function of the twist angle. By substitution it is shown that cis‐L, cis‐R, trans‐L and trans‐R enantiomers are all possible. The consistency of these orbitals is shown by their interconversion upon mirror reflection and their reduction to those of orthogonal and planar allenes. For a doubly degenerate excited state in D2d, it is demonstrated that the Jahn—Teller effect due to the torsional vibration of pseudoscalar symmetry can have an equal chance of generating left or right (D2) enantiomers in a symmetrical double‐well potential. A second‐order interaction with circularly polarized light, that is also of pseudoscalar symmetry, is derived and shown to destroy theoretically the parity of the double‐well resulting in a preference for one enantiomer over the other. The magnitude of this radiative interaction and the time factors relative to tunneling frequency are briefly discussed. Potential use of this pseudoscalar and “chiral” vibration in allene as a surrogate for circularly polarized light in asymmetric synthesis is alluded to.
Phase Transfer Catalysis An Account of its Development and Future
Authors: Starks Charles M.
Published: November 2013

That part of chemistry which has come to be known as “Phase Transfer Catalysis,” or simply “PTC” presents to those of us who have watched and participated in its developments for the last 20 years with a rather classical picture of how and why scientific knowledge becomes generated, recognized, communicated, and eventually absorbed into our box of common and useful tools for practicing chemistry. The first PTC results, scattered over the world in the hands of many independent chemists, gave birth to the concept of Phase Transfer Catalysis, and the formal recognition of this and related concepts brought together a number of people who built the basic theoretical foundation on which PTC rests, who discovered many of the experimental facets of PTC, and who suggested many of the ideas for future development. This “PTC” Past has evolved into the “PTC Present,” which is following a still sharply‐increasing learning curve, with the development of new uses, methods, concepts, theoretical development, and world‐wide recognition. The “PTC Future” is thought by this author to be bright, not through its simple extension to old chemical reactions but because it provides a tool to handle future chemical problems in highly material‐ and energy‐efficient ways.
Studies on Methylation of Anomeric Hydroxyl Groups Under Phase‐Transfer Catalysed Conditions
Authors: Szeja Wieslaw
Published: November 2013

Reaction derivatives of monosaccharides possessing a free anomeric hydroxyl group with methyl sulfate under phase‐transfer catalysed conditions is described. Under phase‐transfer conditions, which permit equilibrium control, the proportions of α‐ to β‐glycosides are determined by the relative acidity of anomers. In the presence of alcohols the proportions of α to β‐D‐gluco‐ and galactopyranosides have been shifted in favor of the equatorial anomer.
Dehydrating Effect of Concentrated Aqueous Alkaline Solutions in Aliphatic Nucleophilic Substitutions Carried out in Aqueous‐Organic Two‐Phase Systems. The Different Behavior of Various Phase‐Transfer Catalysts: Quaternary Salts, Crown Ethers and Cryptands
Authors: Landini Dario , Maia Angelamaria , Montanari Fernando
Published: November 2013

Concentrated aqueous NaOH and KOH solutions affect the hydration and hence the reactivity of anions (Cl−, Br−, I−, SCN−, N−3) in aliphatic nucleophilic substitutions catalyzed by lipophilic quaternary onium salts, cryptands and crown ethers under phase‐transfer (PTC) condtions. In the presence of aqueous 50% NaOH or 53% KOH non‐hydrated anions are transferred from the aqueous into the organic phase by quaternary salts. The anionic reactivity thus becomes identical to that found under anhydrous homogeneous conditions in non‐polar organic media. Unlike quaternary salts, in the presence of cryptates water is not completely removed even at the highest KOH concentration, i.e. conditions in which aH2O ∼ 0. Residual hydration depends on the nature of the anion and is the highest for anions with localized and/or less polarizable charge, such as Cl−, Br− and N−3. As a consequence, rate constants noticeably increase in comparison with those found under conventional PTC conditions, but don't reach those of anhydrous solutions. Behavior of crown ethers is in between that of quaternary salts and cryptates, since residual hydration in the presence of 53% aqueous KOH is lower than that of cryptates, whereas anionic reactivity become practically identical to that found under anhydrous conditions. A comparison of the catalytic efficiency of lipophilic quaternary salts, cryptands and crown ethers under various reaction conditions is also included.
Quaternary Onium Salts Immobilized on Inorganic Matrices
Authors: Tundo Pietro , Venturello Paolo , Angeletti Enrico
Published: November 2013

Onium salts immobilized on silica gel and alumina show unusual properties because of the presence of the polar inorganic support. Under liquid—liquid phase‐transfer catalysis conditions these systems can also catalyze reactions carried out without stirring, and unlike the corresponding onium salts supported on polystyrenic matrix, they do not need the use of polar solvent. Moreover, different matrices with different geometries in the micropores are differently functionalized and may induce selectivity towards reagents with different molecular size. The polar and hydrophilic matrix strongly affects the affinities of the immobilized onium salts in the anion exchange process, producing a higher affinity towards hydrophilic inorganic and lipophilic organic anions, with respect to that observed for the homogeneous and polystyrene supported onium salts. In aqueous solution the onium salts supported on inorganic matrices are able to adsorb the reactants and to vary the reaction microenvironment as the micellar catalysts do.
The Geometrical Nature of Transition State Variation
Authors: Harris J. Milton , Paul J. Lawrence
Published: November 2013

The proposal that the movement of transition states on potential energy surfaces is controlled by the geometry of the surface is examined by use of a nonchemical, mathematical model of surfaces. We conclude that the chemical rules of Thornton, Jencks, and More O'Ferrall for predicting TS movement have an underlying geometrical origin. The model permits ready visualization of the rules for predicting TS movement, and the model facilitates predicting TS movement for surfaces in which the saddle point lies off the diagonals connecting the corners of the surface.
Temperature Dependence of the Radical Addition to Alkenes
Authors: Giese Bernd , Feix Christine
Published: November 2013

In addition reactions of primary n‐hexyl, secondary cyclohexyl and tertiary butyl radicals to the alkene pair fumarodinitrile/methyl α‐chloroacrylate, the selectivities and the differences of the selectivities decrease with increasing temperature. An isoselective relationship is found with an isoselective temperature of about 280°C. Below this temperature, the frontier molecular orbital theory can be applied to explain the substituent effects on the selectivities. The previously observed breakdown of the reactivity‐selectivity principle for radical addition reactions to alkenes is, therefore, not a temperature effect.
A Demonstration of the Reactivity—Selectivity Principle for the Thiol—Disulfide Interchange Reaction
Authors: Hupe D.J. , Pohl E. R.
Published: November 2013

Equilibrium constants for the reaction of aryl thiol anions with hydroxyethyl disulfide have been measured which, along with literature data, demonstrate a slope of 1.21 for a plot of log KS− (R'S‐ + RSSR ⇌ R'SSR + ‐SR) vs pKa. Rate constants were measured also for these endothermic reactions of aryl thiol anions with hydroxyethyl disulfide and also for the exothermic reactions of alkyl thiol anions with the mixed disulfide of mercaptoethanol and 4‐nitro‐2,3,5,6‐tetrafluorothiophenol. These kinetic data, obtained over a range of KS− of 1021, show the gradual curvature expected for Hammond postulate type behavior. A quantitative measure of this curvature in terms of the Marcus formalism was carried out for these two data sets along with four others having more moderate values of ΔG. The data were fit with a value for the intrinsic barrier, λ/4 = 11.6 kcal, and a value for the work term Wr = 4.0 kcal. A comparison is made of these values with the similar values found for alkyl, proton and acyl transfer reactions. The importance of using a variety of substrates with a series of bases or nucleophiles, rather than a single substrate, is discussed, as are the cause for curvature other than Hammond postulate behavior.
Cation—Anion Combination Reaction of Substituted Tropylium Ions with Borohydride Ion in Acetonitrile: Regioselectivity in a Diffusion‐Controlled Region
Authors: Takeuchi Ken'ichi , Yasuda Sumio , Kitagawa Toshikazu , Senzaki Yoshihide , Okamoto Kunio
Published: November 2013

The relative rates and regioselectivities were determined for the reaction of unsubstituted and substituted tropylium ions containing methoxy, methylthio, methyl, phenyl, methoxycarbonyl or cyano with borohydride ion in acetonitrile at 25°C. The rate increases in the order methoxy‐ < methylthio‐ < methyl‐ < unsubstituted‐, but it levels off for unsubstituted‐, phenyl‐, methoxycarbonyl‐ and cyano‐tropylium ions. From the lower limit of the rate constant of the methoxytropylium ion, which was estimated by the stopped‐flow technique, and the logarithmic plot of the relative rates against those of the one‐electron reduction of the tropylium ions with Cr(II) ion, the reaction with the borohydride ion at the level‐off region was concluded to be diffusion‐controlled. In spite of the diffusion‐controlled behavior, these tropylium ions show regioselectivities. The data indicate that the present cation—anion combination reaction is not a one‐step reaction, but proceeds via a cation—anion encounter‐pair (or charge‐transfer) intermediate, providing a clear example of the presence of intramolecular selectivity in the absence of intermolecular selectivity. CNDO/2 SCF MO calculations suggest that the regioselectivity is primarily frontier orbital controlled.
Constant Selectivity in Proton Exchange Reactions Between Aqueous Sulphuric Acid and Acetylenes
Authors: Chokotho Norris C. J. , Johnson C. David
Published: November 2013

Linear Pfluger plots of unit slope are obtained from logarithmic rate constants for acid–catalysed hydration of phenylacetylene and its substituted derivatives p‐OCH3, p‐CH3, m‐CH3, p‐Br, m‐Cl, m‐NO2, p‐NO2 in aqueous sulphuric acid solution. This direct experimental observation of absence of any dependence on selectivity gives evidence for the applicability of the magnified image kinetic acidity function in these systems.
Ionization of Acetylacetone in Me2SO—Water Mixtures. Reactivity—Selectivity Principle or Principle of Imperfect Synchronization?
Authors: Bernasconi Claude F. , Bunnell Richard D.
Published: November 2013

Rate constants for the reversible deprotonation of acetylacetone were measured in carboxylate and amine buffers in water and in 50%, 90% and 95% Me2SO at 20°C. The Brønsted plot for the carboxylate ions is curved in the Me2SO—water mixtures, but straight in water. The curvature is in the direction predicted by the Reactivity—Selectivity Principle (RSP). However, the Brønsted plot for the reaction with primary amines is straight in all solvents. This suggests that the curvature observerd with the carboxylate ions is caused by loss of solvation of the base; this loss of solvation is ahead of bond formation in the transition state rather than being a manifestation of the RSP. (Note that all Brønsted plots are based on pKavalues measured in the respective solvents.) The intrinsic rate constant (k0) for proton transfer increases with the addition of Me2SO, and more so with the carboxylate buffers than with the amines. This increase ink0is attributed to delayed solvation of the developing enolate ion in the transition state; with the carboxylate buffers, an additional factor is the early loss of solvation of the base. The various solvation effects observed in this study can all be understood in the context of the Principle of Imperfect Synchronization (PIS).
Reactions with Aziridines, XXXII[1]. Mechanistic Aspects in Nucleophilic Opening of Three‐Membered Rings. Alcoholyses of Activated Aziridines
Authors: Bucholz B. , Stamm H.
Published: November 2013

Nucleophilic ring opening of three‐membered rings is discussed in terms of leaving group basicity. Reactions of activated (weakly basic leaving groups) 2,2‐dimethylaziridines 5 and 2‐phenylaziridines 6 with alcohols ROH are studied with reference to the site selectivity of ring opening and competing side‐reactions. Abnormal opening (at the substituted carbon) of 5 proceeds in neutral ROH without catalyst when the activation is strong (tosyl) whilst no reaction or mainly carbonyl attack is observed with weak activation (CONHAr). NaClO4 catalyzes the abnormal opening of 5. EtO− gives exclusively normal opening of 5 whilst, in contrast to the literature, MeO− gives also a substantial amount of abnormal ether. Attack on 6 always occurs at both positions with the predominance of the abnormal reaction being greater for MeO− than for EtO−. These reactions are considered SN2 with steric and benzylic differentiation between normal and abnormal attack depending on the size of ROH. Acid catalyzed openings of 5 and 6 proceed exclusively abnormally in the ether‐forming reaction as well as in side‐reactions. Competition experiments and increase of the side‐reactions with the size of ROH demonstrate a deceleration of the ether‐forming reaction with the size of ROH. Obviously, the side‐reactions originate from a carbenium ion whilst the ethers are mainly formed by a borderline mechanism. R(‐)6b and acidic MeOH give only 8% racemization in the abnormal ether. An order of activation is proposed for activated aziridines under acid catalysis (double activation).
The Synthesis of Vicinal Diacylamines via Bamberger Ring Cleavage of Substituted Imidazoles. 1,2,4‐Triacylaminobutanes Bearing Different Acyl Groups
Authors: Altman Janina , Shoef Nurit , Wilchek Meir , Warshawsky Abraham
Published: November 2013

Bamberger ring cleavage acylation of N‐p‐toluenesulfonyl (tosyl) histamine followed by hydrogenation yields 3,4‐diacylaminobutanetosylamine, a triamine containing groups with different chemical reactivities.
The Chichibabin Amination of 5‐Phenylpyrimidine and Phenylpyrazine [1,2]
Authors: Breuker K. , van Der Plas H.C. , van Veldhuizen A.
Published: November 2013

5‐Phenylpyrimidine (1) on treatment by KNH2/NH3, affords a mixture of 2 amino‐ and 4‐amino‐5‐phenylpyrimidine. The presence of only the anionic C‐4 adduct. 4‐amino‐5‐phenyl‐1 (or 3), 4‐dihydropyrimidinide was shown by 1H‐ and 13C‐NMR spectroscopy of a solution of 1 in KNH2/NH3. Study of the amination by use of 15N‐labelled KNH2/NH3 convincingly shows that in the formation of the 2‐amino compound a ring opening‐ring closure sequence is involved. The amination of phenylpyrazine (11) into 5‐amino‐ and 3‐amino‐2‐phenylpyrazine has been found to occur without opening of the pyrazine ring. Examination by 1H‐ and 13C‐NMR spectroscopy of a solution of 11 in KNH2/NH3, reveals that at −60°C three adducts are present; i.e. 3‐amino‐, 5‐amino‐ and 6‐amino‐2‐phenyl‐dihydropyrazinides, at −40°C the C‐3 and C‐5 adducts are formed; and at room temperature only the thermodynamically most stable C‐5 adduct is present.
A New Route to Macrocycles Possessing the 2,6‐Pyridino Subunit via Bis‐1,3‐Dithianes [1]
Authors: Newkome George R. , Lee H.W. , Fronczek Frank R.
Published: November 2013

Two rigid crown ethers 12, which possess a terpyridine subunit, are herein prepared by the construction of the middle pyridine moiety via a bis‐dithiane precursor. The intermediate diketone and derivatives are sufficiently mobile to permit macrocyclization; then their irreversible conversion to a pyridine nucleus circumvents the inherent structural constraints associated with the synthesis of these macromolecules.
Design of New Calcium Antagonists. 4‐Aryl‐1,4‐Dihydropyrimidine‐5‐Carboxylates from Olefinic Acetoacetic Esters and Amidine via Regiospecific Ring Closure [1]
Authors: Weis Alexander L. , Vishkautsan Rozita
Published: November 2013

5‐Functionalized‐l,4‐dihydropyrimidines (5) were prepared via a twostep reaction between arylidene acetoacetic esters (1) and amidines (2). Intermediate 6‐hydroxytetrahydropyrimidines (4) were isolated under mild conditions, and subsequently dehydrated by heating in glacial acetic acid. Warming a solution of 1a and 2a, without isolation of the intermediate product, afforded 5‐acetyl‐6‐oxo‐1,4,5,6‐tetrahydro‐pyrimidine (3), indicating ring closure via the α,β‐unsaturated ester fragment of 1. The mechanism of formation and structure of cyclic adduct intermediates 4, and final dihydropyrimidines 5 are discussed.
Molecular Dynamics Simulations of DNA Double Helices: Studies of Sequence Dependence and the Role of Mismatch Pairs in the DNA Helix
Authors: Rao Shashidhar N. , Chandra Singh U. , Kollman Peter A.
Published: November 2013

We present the results of molecular dynamics simulations on base paired deoxyribonucleotides dA10·dT10, d(GCGCGCGCGC)2 d(ATATATATAT)2 d(CGCGA)·d(TCACG) (AC mismatch) and d(CGAGA)·d(TCGCG) (GA mismatch). The average structural properties — helix parameters, H‐bond parameters, sugar puckers, torsional angles, root mean square atomic fluctuations — are compared to those found in earlier studies on the sequence d(CGCGA)·d(TCGCG).1 The properties of the decamer helices remain B DNA like throughout the simulation, confirming our inference1 that a model which treats solvent/counterions in a simple fashion (full charge on phosphates, but use of large hydrated counterions and a distance dependent dielectric constant) is a reasonable “first order” model to simulate the properties of DNA helices over periods of at least 100 psec. There are a number of sequence dependent effects observed in the three decanucleotides studied here, among them differences in H‐bond properties, sugar pucker and helix repeat/base tilts. In d(GCGCGCGCGC)2 and d(ATATATATAT)2 the H‐bonds all stay near the classic Watson‐Crick distance and the base tilts and twists are small (10–20°). On the other hand, in dA10·dT10 there are much larger deviations of H‐bonding from classic Watson‐Crick and H‐bond exchange during the simulation. There are many more examples of sugar repuckering in the AT decamers, and the relative frequency of such repuckering is qualitatively consistent with what one would expect based on molecular mechanics studies. A comparison of the torsional angles, sugar puckers, helical parameters, root mean square atom amplitudes and hydrogen bond parameters of the sequence d(CGCGA)·d(TCGCG) with the two mismatched analogues demonstrates that the effect of the poorer hydrogen bonding at the central base pair is transmitted throughout the sequence, leading to significantly greater root mean square fluctuations in all dihedral angles, significantly higher % of non‐“standard C2′ endo” sugar puckers, generally longer H‐bond distances, with greater % of “long” H bonds during the simulation, larger RMS amplitude of atomic fluctuations and greater helix twist and tilt of the base pairs. The average helix repeat is 9.0 for the AC mismatch, and 10.1 for the GA mismatch, compared to 10.0 for the normal sequence.
Computer Simulation and the Design of New Biological Molecules
Authors: Wong Chung F. , Andrew McCammon J.
Published: November 2013

Molecular dynamics simulations have been carried out for the enzyme bovine trypsin, for the small inhibitor benzamidine, and for the complex formed by these two molecules, all in the presence of enough water to approximate dilute solution conditions. The simulations have been analyzed to characterize the structure and dynamics of the enzyme and its solvent surroundings. Using the recently developed thermodynamic cycle‐perturbation method, the simulations have also been analyzed to determine how changes in the structure of the enzyme and the inhibitor alter the free energy of complex formation. The results suggest that such simulations may be useful in the design of new enzymes and enzyme inhibitors.
The Free Energy of Xenon Binding to Myoglobin from Molecular Dynamics Simulation
Authors: Hermans J. , Shankar S.
Published: November 2013

The interaction of xenon atoms with the interior of the myoglobin molecule has been simulated by molecular dynamics calculations. The standard free energy of binding has been computed from a simulation in which a forcing potential was applied; computed and experimental values differ by only 2 kJ/mole. In agreement with experimental evidence, the simulations indicate that insertion of the first xenon atom causes a perturbation of the protein conformation that facilitates insertion of one or more additional xenona.
Ligand Substitution Reactions of Transition Metal Organometallic Complexes and Homogeneous Catalysis
Authors: Basolo Fred
Published: November 2013

Transition metal organometallic homogeneous catalysts depend on the ease of ligand substitution in one or more of the catalytic steps. Thus, it follows that the more we learn about the factors which affect rates of ligand substitution, the better we will be able to design useful catalysts. Three different types of approaches to the enhancement of ligand substitution are discussed. These are (1) through the use of spectator ligands which permit an 18‐electron system to react by an associative process, (2) the relative rates of substitution of a 17‐electron and a corresponding 18‐electron system, and (3) the reactivity order 1st row < 2nd row > 3rd row transition metals for a given metal triad. Specific examples are given for each of these approaches to generate more substitution labile organometallic compounds.
Homogeneous Catalysis. Mechanisms of Metal Catalysed Claisen Rearrangements of O‐allylic‐S‐methyl dithiocarbonates
Authors: Auburn P.R. , Whelan J. , Bosnich B.
Published: November 2013

A number of catalysts of Pd(II), Pt (II), Rh (I) and Ir(I) induce rearrangements of O‐allylic‐S‐methyl dithiocarbonates at 25° C. For most substrates, the Pd(II) and Pt(II) catalysts cause [3,3] sigmatropic (Claisen) rearrangements but the Rh(I) and Ir(I) catalysts give, in addition, other products depending on the catalyst and the substrate. The Claisen rearrangements observed with the Pd(II) and Pt(II) catalysts are believed to occur by a cyclization induced mechanism, whereas those rearrangements associated with the Rh(I) and Ir(I) catalysts, as well as in one case with the Pd(II) catalyst, appear to involve metal stabilized carbocation intermediates. When cyclic substrates are used retention of configuration is observed predominantly for all catalysts tried.
The Reaction of Allylbenzene and CoH(CO)4
Authors: Ungvary F. , Marko L. , Bockman T.M. , Garst J.F. , King R.B.
Published: November 2013

The carbon monoxide uptake in the reaction of allylbenzene with CoH(CO)4 in n‐octane leading to acylcobalt tetracarbonyls and aldehydes is catalyzed by Co2(CO)8. The rate is half order in Co2(CO)8, first order in allylbenzene and shows a complex dependence in CoH(CO)4 and CO. From kinetic experiments between 15 and 45° C the temperature dependence of the observed rate constant was determined. The complete analogy of this kinetics with that obtained for heptene‐1 shows that the main aldehydic product 2‐phenylbutyraldehyde is formed by a mechanism characteristic for aliphatic olefins and not by one operative for styrenes.
Oxidation of para‐ and meta‐ Cresols by C‐ Meso‐5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane‐Nickel (III), to the Corresponding Aldehydes in Aqueous Media
Authors: Uzan Y. , Meyerstein D.
Published: November 2013

The tervalent nickel complex with C‐meso‐ 5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane, Ni‐(III)L, as its disulphate form, Ni(III)L(SO4)2, oxidizes cresols in aqueous solutions. The major products after two electron equivalents are consumed are the corresponding hydroxybenzyl alcohols. The products after four electron equivalents are consumed are the corresponding hydroxybenzaldehydes. Excess tervalent nickel does not lead to the formation of the corresponding hydroxybenzoic acids. The results indicate that the oxidation reactions observed occur via the outer sphere mechanism. The use of NiL2+ as a catalyst for the oxidation of cresols is discussed.
Origin of the Multi‐dimensional Properties and the Charge Distribution Rule of the Molecular Conductors Based on π‐Donor and π‐Acceptor Molecules
Authors: Kobayashi Hayao , Kato Reizo , Kobayashi Akiko
Published: November 2013

The new aspects of molecular conductors are reviewed. The origin of the two‐dimensionality of the system is interpreted on the basis of the simple tight‐binding band examinations. The charge distribution rule which emerges in these systems is described in relation to the multi‐dimensionality of these complexes.
Conducting and Superconducting BEDT‐TTF Based Synmetals
Authors: Wang Hau H. , Beno Mark A. , Whangbo M.‐H. , Emge Thomas J. , Geiser Urs , Douglas Carlson K. , Venturini Eugene L. , Williams Jack M.
Published: November 2013

The synthesis, crystal structures and band electronic structures of BEDT‐TTF based synmetals are discussed, where BEDT‐TTF is bis(ethylenedithio)‐tetrathiofulvalene here abbreviated to “ET”. The electrical properties of ET:X salts above their phase transitions are either 1D [for (ET)2X, where X− = ICl2−, AuBr2−, Au(CN)2− and Ag(CN)2−], 2D metallic [for (ET)2X, where X− = I3−, AuI2−, IBr2− and I2Br−] or 3D metallic [for (ET)Ag4(CN)5]. The β‐(ET)2X (X− = I3−, AuI2− and IBr2−) salts become ambient pressure organic superconductors at 1,4 K (or ∼ 8 K under pressure), 5.0 K, and 2.8 K, respectively. The variation of critical temperatures of this series of β‐(ET)2X salts are correlated to the respective changes in unit cell volume or in the density of electronic states at the Fermi level.
Electrical and Spectroscopic Properties of TTF and TSF Salts with Tetrahalogenozinc(II) and ‐cadmium(II) Anions
Authors: Tanaka Atsushi , Matsubayashi Gen‐Etsu , Tanaka Toshio
Published: November 2013

Several tetrathiafulvalene (TTF) and tetraselenafulvalene (TSF) salts of tetrahalogenozinc(II) and ‐cadmium(II) anions Dx [MX4] (D = TTF or TSF; M = Zn and Cd; X = Cl, Br, and I; x = 2.0‐6.6) have been prepared by the reaction of [TTF]3[BF4]2 or [TSF]3[BF4]2 with [NEt4]2[MX4] in acetonitrile and by the electrolysis of TTF or TSF in acetonitrile containing [NEt4]2[MBr4]. Electrical resistivities of these salts measured for compressed pellets fall in the range 1 × (101–107) Ω cm at 25 °C; the value decreases with increasing bulkiness of the anions: [MCl4]2– > [MBr4]2− > [MI4]2−. Stackings and electronic states of TTF and TSF molecules are discussed on the basis of electronic reflectance, ESR, IR, and Raman spectra.