bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereospecific reaction of isopropyl methylphosphonofluoridate (sarin) with α‐cyclodextrin: A model for enzyme inhibition
Authors: van Hooidonk C. , Breebaart‐Hansen J. C. A. E. 
Published: September 2010

AbstractThe rates of alkaline hydrolysis of the enantiomers of isopropyl methylphosphonofluoridate (Sarin) have been determined without and with varying concentrations of α‐cyclodextrin (cyclohexaamylose) in aqueous 0.1M/‐KCl solution at pH 9.0 and 25°.The pseudo first‐order rate constants are reported. The observed kinetics and product analysis are consistent with a reaction scheme in which complex formation precedes the nucleophilic reaction of α‐cyclodextrin with Sarin. Dissociation constants (Kdiss) of the inclusion complexes and rate constants (k2) for the nucleophilic reaction are reported. The results indicate a stereospecific formation of the inclusion complexes, (S)‐(+)‐Sarin forming a more stable complex than (R)‐(‐)‐Sarin, as well as a stereospecific rate of reaction, (R)‐{‐)‐Sarin reacting faster than (S)‐(+)‐Sarin. The α‐cyclodextrin‐Sarin system represents the first model reaction for enzyme inhibition showing typical properties as complex formation, saturation effects and stereospecificity.
Rearrangements of 1,2,3,4,5‐, 1,2,4,4,5‐, 1,3,4,4,5‐ and 1,2,3,4,4‐pentamethylcyclopentenyl ions and of 1,3,4,4,5,5‐ and 1,2,3,4,4,5‐hexamethylcyclopentenyl ions. stability of pentamethylcyclopentenyl ions
Authors: Brouwer D. M. , van Doorn J. A. 
Published: September 2010

AbstractA detailed investigation has been made of the reversible rearrangement of the 1,2,3,4,5‐pentamethylcyclopentenyl ion (1) to the 1,2,3,4,4‐pentamethylcyclopentenyl ion (3). In 5: 1 FSO3H‐SbF5 this reaction proceeds entirely intramolecularly by 1,2‐hydrogen and methyl shifts via three allylic and four non‐conjugated tertiary pentamethylcyclopentenyl ions as intermediates. Two of the intermediate allylic ions have been prepared by cyclization of the 2,4,6‐trimethylheptadienyl ion and their rearrangements have been further investigated.Rate constants of the various rearrangements are reported and a detailed free‐energy profile of these reactions is presented.The 1,3,4,4,5‐pentamethylcyclopentenyl ion (4) is 4.7, and the 1,2,4,4,5‐isomer (5) 10.0 kcal · mole−1 less stable (in terms of ΔF at 50°) than 1; these large differences are partly ascribed to the crowding of the three methyl groups on C4 and C5 in the former two ions.The cation 1 occurs as cis and trans isomers, which are formed in a 1: 1 ratio upon protonation of the diene, and in a 2.3: 1 ratio upon rearrangement of 5 and 4. Their equilibrium ratio is 0.37: 1, which may indicate a non‐planar structure for this ion.Our re‐examination of the cyclization of the 2,4,6‐trimethylheptadienyl ion in FSO3H‐SbF5 gave results considerably different from those reported by previous workers.In the 1,2,3,4,4,5‐hexamethylcyclopentenyl ion (2) degenerate equilibrations through alternating hydrogen and methyl shifts cause line broadening in the PMR spectrum above 120°. These shifts are faster than the corresponding shifts of hydrogen in 1 and of methyl in 3, respectively, which is attributed to a steric acceleration due to the crowding of the three methyl groups on C4 and C5 in 2. Similar steric effects are held responsible for the fact that the rearrangement of 1,3,4,4,5,5‐hexamethylcyclopentenyl ion to 2 is much faster than that of 4 to 1 and 3, and that in 5 the methyl shift is almost as fast as the hydrogen shift.
1,3‐Oxathioles as intermediates in nucleophilic additions to 1‐Acylthio‐1‐Alkynes. II
Authors: Drenth W. , de Gruijter H. J. 
Published: September 2010

AbstractIn aqueous solution, 1,3‐oxathioles (IV; R″ = alkyl), are rapidly hydrolysed to II and subsequently converted into 1‐acylthio‐2‐alkanones (III) at a rate proportional to [OH⊖]. The solvent deuterium isotope effect of the latter conversion amounts to 1.82 ± 0.05. These data support a mechanism involving rapid deprotonation, followed by rate‐determining ring opening.
Alkyl‐ and Aryl‐Thiolation.: A kinetic study with bis‐phenylsulfonylmethane
Authors: Bosscher J. K. , Kloosterziel H. 
Published: September 2010

AbstractThe kinetics of the reaction of bis‐phenylsulfonylmethane with thiosulfonic esters (RSSO2R′) have been measured in 100% ethanol, in the presence of triethylamine, at 20°. The kinetic data on the substitution of an ‘active’ hydrogen by a thioaryl or thioalkyl (RS) group are compatible with a two‐step mechanism. First the carbanion of bis‐phenylsulfonylmethane is formed by action of the base after which a bimolecular reaction occurs between the carbanion and the thiosulfonate. The reaction is retarded by introduction of electrondonating substituents in both R and R′. The possible structure of the transition state is discussed.
The assignment of the vibrational frequencies of the SO3Cl− Ion
Authors: Stufkens D. J. , Gerding H. 
Published: September 2010

AbstractThe Raman spectra of HSO3Cl in CH3COOH and NaSO3Cl in N,N‐dimethylacetamide are recorded. From these spectra the SO3Cl− frequencies are reassigned. The new assignment is in agreement with the Raman spectra of solid (CH3)4N · SO3Cl, SCl4 · SO3, SeCl4 · SO3 and TeCl4 · SO3.
An NMR Study of intramolecular shielding in Alkyl N(Arylsulfonyl)Methyl]‐Carbamates, ‐Thiolcarbamates, ‐Thionocarbamates, and ‐Dithiocarbamates
Authors: van der Werf S. , Engberts J. B. F. N. 
Published: September 2010

AbstractThe chemical shifts of the ester alkyl groups of alkyl N‐[(arylsulfonyl)methyl]‐carbamates are displayed as doublets of unequal intensity at temperatures where rotation around the nitrogen to carbonyl bond is slow on the NMR time scale.Comparison with NMR data of simple alkyl N‐substituted carbamates indicates that the ester alkyl absorption of at least one of the rotamers shows an appreciable upfield shift. These upfield shifts are dependent on the ring current in the aromatic nucleus of the molecule. An explanation for these observations is presented in terms of preferred conformations (with minimized lone pair‐lone pair repulsion) in which the ester alkyl group is situated above (or below) the plane of the aromatic ring. Minor structural changes in the molecule eliminate the shielding effect which supports the proposed shielding mechanism. Further evidence for intramolecular shielding was obtained from the observed solvent and temperature dependence of the chemical shifts of the ester alkyl protons. No evidence could be obtained for inter‐ or intramolecular association between the aromatic ring and the ester function.Chemical shift data for alkyl N‐[(arylsulfonyl)methyl]thiolcarbamates, ‐thionocarbamates and ‐dithiocarbamates also indicate intramolecular shielding of the ester alkyl protons.
Homogeneous hydrogenation of substituted cinnamic acids with pentacyanocobaltate(II)
Authors: Basters J. , van Bekkum H. , van Reijen L. L. 
Published: September 2010

AbstractThe homogeneous hydrogenation of a series of substituted trans‐cinnamic acids with pentacyanocobaltate(II)‐ion has been investigated. The reactions were found to be first order in pentacyanohydridocobaltate(III) as well as in substrate, and zero order in cyanide. Electronic substituent effects may be expressed in terms of a Hammett‐Yukawa relationship with ρ = 0.67. In the hydrogenation of cis‐cinnamic acid partial isomerization to the trans‐isomer was observed. The deuteration of cis‐ and trans‐cinnamic acid and the hydrogenation of α,β‐dideutero‐cis‐cinnamic acid have been studied. The results can be understood by considering the reaction as a stepwise hydrogen atom transfer from the hydride to the substrate.
Mass spectra of α,β‐substituted butenolides
Authors: Reinhoudt D. N. , van de Graaf B. 
Published: September 2010

AbstractThe mass spectra of twenty‐six β‐ and α,β‐substituted butenolides have been examined. Fragmentation of the butenolide ring can be rationalised on the basis of the fragmentation pathways described for β‐hydroxybutenolides. However, a number of butenolides, e.g. the α‐(substituted)benzamido‐β‐hydroxymethyl‐butenolides, show a weak fragmentation of the ring. The fragmentations in which the substituents are involved are more favourable and interactions between the substituents on the α‐ and β‐positions complicate these spectra.
The reaction of acetals with bromine in sulfur dioxide
Authors: Dusseau Ch. H. V. , Schaafsma S. E. , de Boer Th. J. 
Published: September 2010

AbstractThe reaction of bromine with a variety of dimethyl acetals at − 60° in sulfur dioxide is described. Electrophilic attack of bromine on oxygen leads to methyl hypobromite (CH3OBr) together with mono methoxycarbenium bromide or ‐ depending on the stability of the cation ‐ its covalent counterpart, the α‐bromo‐ether. The reaction is catalysed by acids. Acetals derived from linear and cyclic carbonyl compounds react in this way with one exception: with 1,1‐dimethoxycyclopropane, the acetal of cyclopropanone, electrophilic attack by bromine is not on oxygen, but on the cyclopropane ring. Ring rupture leads to a relatively stable di methoxycarbenium ion.
Complex formation between organic nitro compounds and sulfur trioxide
Authors: Cerfontain Hans , Koeberg‐Telder A. 
Published: September 2010

AbstractNMR evidence is presented for complex formation between nitromethane and sulfur trioxide in thrichlorofluoromethane as solvent according to . In addition, kinetic evidence for complex formation between nitrobenzene and sulfur trioxide in trichlorofluoromethane was obtained from sulfonation studies of that system.
Pyrazoles and Imidazoles as ligands. Part III: Coordination compounds containing 3(5)‐methylpyrazole and metal(II) salts
Authors: Reedijk J. 
Published: September 2010

AbstractA number of compounds with general formula M2+(MPZ)n(anion)2 is reported, in which M = Mn, Fe, Co, Ni, Cu, Zn and Cd; MPZ = 3(5)‐methylpyrazole, n = 2–7, and the anions are ClO4, −, BF4, −, NO3, −, CNS−, Cl−, Br−, I−.The compounds are characterized by chemical analyses, X‐ray powder diagrams, ligand‐field spectra, paramagnetic susceptibility and resonance measurements, and vibrational spectra.The ligand MPZ is found to coordinate via the imino lone pair electrons, with the methyl group most probably located in the 5‐position, trans to the coordinated metal ion.With respect to the same anion, groups of isomorphous compounds were found according to the X‐ray powder patterns. Ligand‐field spectra of the coloured transition‐metal ion complexes indicate that MPZ is a stronger coordinating ligand than the unsubstituted pyrazole. This is confirmed by the magnetic susceptibility measurements and the paramagnetic resonance spectra.Fairly regular octahedral groups M(MPZ)6 2+ are found for the compounds with perchlorate and tetrafluoroborate anions (except for Cu2+), whereas strongly distorted tetragonal groups M(MPZ)4(anion)2 are found for the compounds containing the other anions (and for the Cu2+ compounds with BF4 − and ClO4 − anions). Infrared spectra of these latter compounds confirm the coordination of the ClO4, −, BF4− and NO3− anions, since split anion absorptions are found.
Synthesis of some 3‐deoxy‐heptulosonic acids
Authors: Paerels G. B. , Geluk H. W. 
Published: September 2010

AbstractThe detailed syntheses of 3‐deoxy‐D‐arabino‐ and 3‐deoxy‐D‐lyxo‐heptulosonic acids are described. The arabino isomer was purified by LLC on cellulose. In the arabino series an enolized 2‐keto‐1,4‐lactone and in both the arabino and lyxo series 2‐keto‐imido‐1,4‐lactones were isolated. The chemical and spectroscopic properties of these compounds are discussed. A number of other derivatives are described. The UV spectra of the semicarbazones of 2‐keto‐acids and their lactones or esters are discussed. The structure of a quinoxaline derivative of the 3‐deoxy‐D‐arabino‐heptulosonic acid has been studied.
Model studies for enzyme inhibition. Part II: The stereospecific reaction of isopropyl p‐nitrophenyl methylphosphonate with α‐cyclodextrin in aqueous alkaline media
Authors: van Hooidonk C. , Groos Christine C. 
Published: September 2010

AbstractThe rates of alkaline hydrolysis of the enantiomers of isopropyl p‐nitrophenyl methylphosphonate have been measured with and without varying concentrations of α‐cyclodextrin (cyclohexa‐amylose) in aqueous 1.0 M KCl solution at 25° in order to determine the origin of the acceleration of phosphate ester hydrolysis by cyclodextrins.The observed kinetics can be analyzed in terms of a non‐stereospecific binding of both enantiomers to α‐cyclodextrin prior to a nucleophilic reaction of α‐cyclodextrin predominantly with the (R)‐(‐)‐enantiomer. Dissociation constants (Kdiss) of the inclusion complexes and rate constants (k2) of the nucleophilic reaction are reported for the (R)‐(‐)‐enantiomer in dilute alkaline media.From the pH‐dependency of the rate of hydrolysis of the (R)‐(‐)‐enantiomer a kinetic pKa value of 12.6 has been evaluated for the ionization of α‐cyclodextrin.The results also support the suggestion—proposed in the first paper of this series—to use the α‐cyclodextrin‐organophosphorus compound system as a simple model for inhibition of cholinesterases by organophosphorus compounds.
Studies on polypeptides. Part IX: Combination of solid‐phase and classical methods of peptide synthesis in the preparation of 1‐13[13‐Leucine] bovine pancreatic ribonuclease
Authors: Visser S. , Raap J. , Kerling K. E. T. , Havinga E. 
Published: September 2010

AbstractMerrifield's solid‐phase method was applied to the synthesis of all‐L‐glutamyl‐arginylglutaminylhistidylleucine. Azide coupling with all‐L‐Na,Nϵ‐di‐t‐butoxycarbonyllysyl‐γt‐butylglutamylthreonylalanylalanylalanyl‐Nϵ‐benzyloxy‐carbonyllysylphenylalanine hydrazide also prepared on a solid supportS. Visser, J. Roeloffs, K. E. T. Kerling and E. Havinga, Rec. Trav. Chim. 87, 559 (1968).
, resulted in the N‐terminal tridecapeptide sequence of bovine pancreatic ribonuclease in which the methionyl residue, in position 13, has been replaced by leucine. The deblocked and purified product proved to be identical with a sample prepared using conventional methods exclusively.
Inclusion compounds. Part III: Thiourea adducts of some types of cyclohexane derivatives
Authors: van Bekkum H. , Palm J. H. , Verkade P. E. , Wepster B. M. 
Published: September 2010

AbstractThis paper presents the repeat periods of some thirty cyclohexane derivatives, in their respective thiourea adducts as determined by X‐ray diffraction and elemental analysis. In general,trans‐1,4‐substituted cyclohexanes are found to occupy longer sections of the thiourea channel than the correspondingcis‐isomers. In some thiourea adducts the thiourea lattice is deformed as shown by X‐ray data.
Functionalized enamines. Part VIII: Application of dienamines in the synthesis of 6,7‐diazasteroids and polynuclear heterocycles
Authors: Pollmann M. J. M. , Pandit U. K. , Huisman H. O. 
Published: September 2010

Abstract6,7‐Diazasteroidal systems (4a,b) have been prepared by the reaction of dienamines 2a,b with m‐methoxybenzenediazonium fluoroborate in one practical step. The reaction also yields hydrazones 5a,b and 6a,b, as by‐products, which have been converted into certain quinoline (14a, b) and indole (20) derivatives, respectively. Diazasteroid 4a was transformed to 6,7‐diaza‐11‐oxoequilenin‐3‐methyl ether (13).
Conformation of non‐aromatic ring compounds: Part 63. Conformational equilibrium in trans‐1, 2 dihalogenotetralins
Authors: Buys H. R. , Leeuwestein C. H. 
Published: September 2010

AbstractThe conformational equilibrium in trans‐1,2‐dichloro‐ (I), trans‐2‐bromo‐1‐chloro‐ (II) and trans‐l,2‐dibromotetralin (III) is studied with the aid of dipole moments, NMR, infrared and Raman spectroscopy. It appears that the diaxial conformer strongly predominates in solution. The trend in ΔG° on replacing bromine by chlorine as the substituent or carbon tetrachloride by benzene as the solvent is the same as previously found in other vicinal dihalogeno‐substituted compounds. From the IR and Raman spectra it appears that the three compounds crystallize in the diaxial conformation.
Dielectric constant of binary systems. I: An apparent anomaly in the behaviour of ϵ for mixtures of benzene derivatives: Part of this subject matter was presented at the 52nd. Meeting of the asociación física Argentina, July 30, 1969. La Plata, Argentina: (Preliminary Communication)
Authors: Barón Máximo , Rovira Marta , Varela Margarita 
Published: September 2010

AbstractThe dielectric constant as a function of concentration in binary mixtures of (alkyl)benzenes containing toluene as one component was found to be best represented by a 4th. rank polynomial, differing from the generally accepted behaviour of non‐polar liquid mixtures that are represented by a 2nd. rank polynomial.
Alkylation of enolate anions formation of enol ethers
Authors: Heiszwolf G. J. , Kloosterziel H. 
Published: September 2010

AbstractThe alkylation of ambident enolate anions ‐ obtained from aliphatic ketones (and one particular type of aldehyde) ‐ has been studied using various solvents, bases, alkylating agents and substrates. Alkylation with a reactive alkylating agent (dialkyl sulfates, triethyloxonium fluoroborate) in an aprotic polar solvent (e.g. dimethyl sulfoxide) yields mainly enol ethers, the products of alkylation at oxygen. The predominance of alkylation at oxygen over alkylation at carbon in these fast reactions and the behaviour of the various enolate anions are interpreted with the aid of the principle of least motion.
Dynamic Jahn‐Teller effect in the excited states of SeCl62−, SeBr62−, TeCl62− and TeBr62−: Interpretation of electronic absorption and Raman spectra
Authors: Stufkens D. J. 
Published: September 2010

AbstractAlthough the complex‐ions SeCl62−, SeBr62−, TeCl62− and TeBr62− are regular octahedral, the infrared spectra show that some evidence is present for vibronic coupling between ground state and first excited state (dynamic second order Jahn‐Teller effect).The electronic absorption spectra are reported and assignments given. The splittings of the absorption bands closely resemble those found in the spectra of the alkali halide phosphors (KCl: Tl+ etc.). As for the phosphors, an explanation is given in terms of a dynamic Jahn‐Teller effect in the excited states.In connection with this, attention is paid to the unusual intensities of the Jahn‐Teller active modes (eg and t2g) in the Raman spectra of these complex‐ions.
Stereospecific reactions of aryl‐substituted acetylenes in strong proton acids, formation of homocyclopropenyl cations
Authors: Lodder A. E. , Buck H. M. , Oosterhoff L. J. 
Published: September 2010

AbstractTetra‐arylcyclobutenyl cations are formed in quantitative yield in the reaction of diarylacetylenes with strong proton acids. NMR and UV measurements give evidence of a stereospecific cycloaddition reaction of the diarylacetylenes.SCF calculations according to Pariser, Parr and Pople show, that homo‐conjugation must exist in the tetra‐arylcyclobutenyl cations.
Conformation of non‐aromatic ring compounds. Part 67. 220 Mc/s NMR spectra of some six‐membered hetero‐rings having a ‐CH2‐CH2‐CH2‐ fragment
Authors: Buys H. R. 
Published: September 2010

AbstractFrom the 220 Mc/s NMR spectra of 2‐p‐chlorophenyl‐1,3‐dioxane (I), 2‐phenyl‐1,3‐oxathiane (II) and ‐dithiane (III), trimethylene sulfite (IV) and 2‐oxo‐2‐phenoxy‐1,3,2‐dioxaphosphorinane (V) the spin‐spin splitting pattern of the ‐CH2‐CH2‐CH2‐ fragment of the ring is analyzed. The various types of coupling constants (geminal, vicinal and long‐range) are discussed.
Sulfur compounds in free radical reactions. Part IV. Induced decomposition of arenediazothiolates
Authors: van Zwet H. , Reiding J. , Kooyman E.C. 
Published: September 2010

AbstractProduct distributions and rate data of the thermal decomposition of a diazothiolate (Ar‐NNSR) in benzene, chlorobenzene and nitrobenzene as a function of initial diazothiolate concentrations show the reaction to be complex. Three different types of radical‐induced decomposition are discussed.
Complexes with ligands containing the carbonyl group. Part III: Metal (II) acetaldehyde, propionaldehyde and benzaldehyde solvates
Authors: Driessen W.L. , Groeneveld W.L. 
Published: September 2010

AbstractTwenty‐two new coordination compounds are reported with acetaldehyde, propionaldehyde and benzaldehyde as the ligands, viz. M(CH3CHO)6(In‐Cl4)2, M(CH3CHO)6(FeCl4)2, M(C2H5CHO)6(InCl4)2 and M(C6H5CHO)6(In‐Cl4)2 with M is Mg, Mn, Fe, Co, Ni and (except for acetaldehyde) Zn.In the complexes the carbonyl stretching vibration is shifted to lower frequencies compared with this vibration in the free ligands. The magnitudes of the shifts are dependent on the metal ions. Frequency‐shifts of other ligand vibrations are also observed. When the shifts are dependent on the metal ions the magnitudes of the shifts follow the Irving‐Williams sequence.For the acetaldehyde and propionaldehyde solvates a metal‐dependent absorption band appears in the far infrared, which is attributed to the metal‐ligand stretching vibration. This band was not observed in the benzaldehyde solvates.Investigation of ligand field spectra indicated the presence of octahedral species M(O)62+ in the solid compounds. Values for Dq and B for the Co(II) and Ni(II) compounds are reported.A possible relationship between the groups attached to the CO group and the values obtained for the spectrochemical parameter Dq is described.
The influence of solutes on the liquid‐junction potential in the determination of pH in mixtures of an organic solvent and water
Authors: van Veen A. , Hoefnagel A.J. , Wepster B.M. 
Published: September 2010

AbstractBuffer solutions of organic acids in various methanol‐water and ethanol‐water mixtures have been measured with cells I and II:
equation image
Contrary to the generally held opinion, the liquid‐junction potential of cell I is clearly dependent on the solutes in the mixed solvent with higher percentages of organic solvent. The consequences of this for the determination of dissociation constants in mixed solvents with cell I are discussed.
The crystal and molecular structure of 5,7‐dibromo‐2‐(3,5‐dibromo‐2‐hydroxyphenyl)‐2‐methoxymethoxy‐3(2H)‐benzofuranone
Authors: Leenhouts J.I. 
Published: September 2010

AbstractThe compound crystallizes in space group P1, with a = 9.96, b = 8.38 and c= 11.77 Å; α = 73.4, β = 81.3 and γ = 83.5°. There are 2 molecules, related by the centre of symmetry, in the unit cell. Single‐crystal diffractometer, heavy‐atom method and least‐squares refinement were employed. Since only badly shaped crystals could be obtained, interatomic distances and angles are not very accurate. However, the investigation was intended merely to determine the molecular structure. The final weighted R factor is 9.0%, including 1635 three‐dimensional reflections.
Nucleophilic displacements at halogen in 1‐chloro‐, 1‐bromo‐ and 1‐iodo‐1‐alkynes: I. Thiolates as nucleophiles
Authors: Verploegh M. C. , Donk L. , Bos H. J. T. , Drenth W. 
Published: September 2010

AbstractSecond‐order rate constants,k2, of reactions of thiolates with several 1‐aryl‐2‐halogenoacetylenes and 1‐halogeno‐2‐(2‐thienyl)acetylenes were measured in methanol‐water mixtures. Formeta‐ andpara‐substituted 1‐bromo‐2‐phenyl acetylenes these rate constants correlate well with Hammett σ constants: p 1.15. Linear correlations were observed between logk2and pKaof the corresponding thiols.The nucleophilicity constants,n, for substitution on bromine and iodine appear to be quite different from those for substitution on other atoms like carbon, sulfur and platinum. It was possible to correlate all the rate constant withEandHin the oxibase scale ofEdwards.