bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inductive effects on benzene solvent shifts in PMR spectra of (acetylacetonato)‐organoantimony(V) and BIS(acetylacetonato)organotin(IV) compounds
Authors: Mackor A. , Meinema H. A. 
Published: September 2010

AbstractPMR benzene solvent shifts
equation image
and
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have been measured for acetylacetonato protons of hexacoordinate (acetylacetonato)organoantimony(V) and bis(acetylacetonato)organotin(IV) compounds. The observed values correlate better with the inductive effect of substituents at the metal atom than with the molecular dipole moments of these compounds. It is demonstrated that this relation holds also for tetrahedral compounds. The stereochemistry of the benzene‐acetylacetonato group interaction is discussed.
A thermochemical study of some tetra‐alkylammonium bromides in N,N‐dimethylformamide at 25°C
Authors: de Visser C. , Somsen G. 
Published: September 2010

AbstractEnthalpies of solution of some tetra‐alkylammonium bromides (R4NBr, R = ethyl, n‐propyl and n‐butyl) have been determined in N,N‐dimethylformamide (DMF). The concentration‐dependence of the measured heats of solution can be readily accounted for by ionic association, so that measurements at very low concentrations could be avoided. The enthalpies of transfer from water to DMF of the tetra‐alkylammonium bromides deviate substantially from those reported for the corresponding iodides. The differences can be attributed to different transfer enthalpies of the iodide and bromide ions. The enthalpies of transfer of both alkali and tetra‐alkylammonium ions from N‐methylformamide and N‐methylacetamide to DMF are virtually constant, just like those from water and formamide to DMF when the enthalpic effect of solvophobic interaction is taken into account.
Model studies for enzyme inhibition. Part IV: The association of some alkyl methylphosphonates with α‐cyclodextrin in an aqueous medium
Authors: van Hooidonk C. , Breebaart‐Hansen J. C. A. E. 
Published: September 2010

AbstractThe formation of 1:1 inclusion complexes of some alkyl methylphosphonates with α‐cyclodextrin in an aqueous acidic medium has been established. The dissociation constants (Kdiss) of the inclusion complexes have been determined at 25°. The result indicate that non‐polar groups favour the inclusion process.In one case stereospecificity in the formation of the inclusion complex was observed.
Addition des Thiols sur les Cétones. (I): Mécanisme de la réaction d'addition du mercapto‐éthanol sur la cyclohexanone
Authors: Fournier Messieurs L. , Natat A. , Lamaty Messieurs G. , Roque J. P. 
Published: September 2010

The addition reaction of mercapto‐ethanol to cyclohexanone has been measured at 27.0° in solvant Ethanol‐Water “50/50”. The influence of initial thiol and hydronium ion concentrations on the rate of addition and on the equilibrium constant has been especially examined.The reaction obeys general acid catalysis and general base catalysis; the thiol plays a dual role, acting both as a nucleophile and a general base. A mechanism is proposed for this reaction.
Properties of cyclodextrins: Part IX Specific inclusion compound formation of cyclodextrin derivatives with hexane and 2,3‐dimethylbutane in aqueous solution
Authors: Lammers J. N. J. J. 
Published: September 2010

AbstractOn the basis of thermodynamic data concerning inclusion compounds of α and β‐cyclodextrin derivatives with hexane (hex) and 2,3‐dimethylbutane (DMB) in aqueous solution, as reported in earlier publications in this series, a model of the inclusion complex is suggested. This model comprises:
A real inclusion compound (“fit in”) is formed in solution.
Almost all derivatives form inclusion compounds with hex and DMB in which the mole ratio is 1:1 (conclusion of Part VIII of this series).
α‐Cyclodextrin derivatives include in the voids hex molecules in their stretched form, whereas DMB molecules do not fit entirely into the voids. In both cases this causes a considerable disturbance in the water structure around the cyclodextrin molecules.
β‐Cyclodextrin derivatives include hex molecules in their coiled form and DMB molecules fit entirely into the voids. The water structure is hardly affected.
This model appears to be in agreement with considerations of space filling of the guest molecules in the cyclodextrin voids. Furthermore, in comparing the inclusion process with the dissolution of apolar compounds in different solvents, the model is confirmed. Also, comparison of the interaction among the different cyclodextrin derivatives is in agreement with the model.
Reaction of methylpyrazinecarbonitriles and 2‐methylquinoxaline with phosphorus oxychloride and organomagnesium compounds
Authors: Schwaiger W. , Ward J. P. 
Published: September 2010

AbstractIn the preparation of methyl methylpyrazinyl ketones by the sequence methyl‐pyrazinecarboxylic ester, amide, nitrile, to ketone, methylpyrazinecarbonitriles were found to react with phosphorus oxychloride forming tricyclic compounds related to “2‐methylquinoxaline orange”. 2‐Methylpyrazine‐6‐carbonitrile with methylmagnesium iodide underwent addition at one of the ring CN bonds. 2‐Methylquinoxaline reacted similarly with phosphorus oxychloride, and organomagnesium compounds. The methyl methylpyrazinyl ketone described in literature as the 2,6‐isomer was shown to be the 2,5‐isomer.
Chemistry and spectroscopy in strongly acidic solutions. XXXVIII: Stereoisomers interconversion of hexamethylcyclohexenyl cations via a transannular 1,3‐hydride shift
Authors: Hogeveen H. , Kiffen A. A. 
Published: September 2010

AbstractThe mechanism of stereoisomeric interconversion of hexamethylcyclohexenyl cations has been shown to involve two consecutive hydride shifts: a 1,2‐ and a transannular 1,3‐H shift.
Vibrational spectra and structure(s) of X(OR)4 molecules with X  C,: Si and R = methyl, ethyl
Authors: Ypenburg J. W. , Gerding H. 
Published: September 2010

AbstractVibrational spectra of tetramethoxymethane (TMM), tetraethoxymethane (TEM), tetramethoxysilane (TMS) and tetraethoxysilane (TES) have been recorded and assigned. DTA curves and temperature vs. time curves have been recorded in the region −150 to + 30°. No transition points have been observed, melting ranges are −1 to +2 (TMM); −16 to −12 (TEM); +10 to +16 (TMS) and −71 to −68° (TES).The liquid state of tetramethoxymethane (TMM) contains two rotamers; the skeleton C(OC)4 may have S4 or D2d symmetry. The S4 form is about 1 kcal/mole more stable than the D2d form of TMM in the liquid. Solid TMM consists probably of the D2d configuration only.There is no distinction between either configuration in tetramethoxysilane (TMS) as the rotation of methoxy groups around their SiO axes is apparently free for practical purposes.The methyl group of an ethoxy group in X(OC2H5)4 may occupy a gauche or a trans position relative to its XO bond. Rotational isomerism of this kind is probably present in tetraethoxymethane (TEM).Rotational isomerism is probably absent in tetraethoxysilane (TES).
Conformational analysis of some alkyl groups on benzene: PMR spectra of 4‐alkyl‐2‐nitroacetanilides
Authors: Baas J. M. A. 
Published: September 2010

AbstractThe PMR spectra of 2‐nitroacetanilide and often 4‐alkyl substituted derivatives have been measured. Two about equally stable conformers have been detected for the derivatives with the groups ‐CHPriBut, ‐CHBut2, and ‐C(OH)But2. The conformational isomerism is caused by a hindered rotation about the bond between the alkyl groups and the benzene ring; rotational barriers have been determined of approximately 12, 22, and 21 kcal/mole, respectively. The preferred conformations and the rotational barriers are discussed for the alkyl groups ‐CH2But, ‐CHMeBut, and ‐CHPri2.
Chemistry of sulfines, XIV: Benzo[b]thiophene derivatives from dichlorosulfine and diaryldiazomethanes
Authors: Thijs L. , Strating J. , Zwanenburg B. 
Published: September 2010

AbstractThe reaction of dichlorosulfine (Cl2C = S = O) with diaryldiazomethanes, (XC6H4)2C=N2 (X = H, 4‐CH3, 4‐Cl, 3‐OCH3) leads to derivatives of 2‐chlorobenzo[6]thiophene 1‐oxides. The reaction is proposed to proceed via cyclization of an intermediate episulfoxide. Oxidation of 2,2‐dichloro‐3,3‐diphenylthiirane with m‐chloroperbenzoic acid yields 2‐chloro‐3‐phenyl‐benzo[b]thiophene 1,1‐dioxide. This result supports the proposed cyclization mechanism.
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (XXVI): A 15N‐ and 14C‐study of the conversion of chloropyrazine into imidazole with potassium amide in liquid ammonia
Authors: Lont P. J. , van Der Plas H. C. , Bosma E. 
Published: September 2010

AbstractThe mechanism of the conversion of chloropyrazine into imidazole by potassium amide in liquid ammonia has been investigated. It has been proved, using the labelled compounds 2‐chloro‐[1‐15N]pyrazine and 2‐chloro‐[2‐14C]pyrazine, that this ring contraction occurs by a nucleophilic attack of the amide ion on position 3.The synthesis of 2‐chloro‐[2‐14C]pyrazine starting from diethyl malonate labelled in the ethoxycarbonyl group, is described.
NMR Spectra of partially oriented mono‐ and hexa‐fluorobenzene
Authors: Gerritsen J. , Maclean C. 
Published: September 2010

AbstractNMR spectra of fluorobenzene, partially oriented in two different liquid crystals have been measured and interpreted. It is shown that pseudo‐dipolar proton‐fluorine couplings can be neglected in deducing geometrical data from these spectra.From the spectra of partially oriented hexafluorobenzene the indirect nuclear spin‐spin couplings have been determined.
Synthesis of tetra‐alkoxy‐ and tetra‐aryloxyethenes
Authors: Scheeren J. W. , Staps R. J. F. M. , Nivard R. J. F. 
Published: September 2010

AbstractSeveral tetra‐alkoxyethenes have been synthesized from dialkoxy‐monoaryl‐oxymethanes by treatment with sodium hydride. The occurrence of dialkoxy carbenes as possible reaction intermediates is discussed. Best results (45‐60%) were obtained with dialkoxy‐mono‐p‐chlorophenoxymethanes.Tetra‐aryloxyethenes have been prepared by a similar procedure in which diaryloxymethyl chlorides were used as starting compounds.
Vapour phase chemistry of arenes. I: Thermolysis of benzene and derivatives; the effect of additives. Evidence for free radical chain processes
Authors: Louw R. , Lucas H. J. 
Published: September 2010

AbstractThe rate of the conversion of benzene into biphenyl (“tank flow” reactor, atmospheric pressure, nitrogen dilution, 540°) is found to be highly dependent on type and concentration of additives. For example, small amounts of sulfur or oxygen lead to strong retardation, but a little formaldehyde or C2Cl6 has a profound accelerating effect. Wall (memory) effects are also observed.These facts point to a radical chain mechanism ‐ involving H· and phenyl radicals ‐ rather than to a (bi)molecular process as was recently proposed by Fields and Meyerson. Other phenomena (H/D exchange, oxidation to phenol) are also consonant with a (semi)quantitative description based on thermo‐chemical kinetics.The thermolysis of other arenes can be explained analogously; thus, biphenyl (giving benzene, ter‐ and quater‐phenyls) forms H·, C6H5‐C6H4· and phenyl radicals as intermediates, the latter fragments arising through H· + biphenyl → (C6H6‐C6H·5.→ benzene + phenyl.
Polyisocyanides, synthesis and isomerization to polycyanides
Authors: Nolte R. J. M. , Stephany R. W. , Drenth W. 
Published: September 2010

AbstractNi(C2H5OH) (t‐C4H9NC)Cl2 and nickel acetylacetonate are effective catalysts for the polymerization of isocyanides. Protic solvents and the presence of an acid accelerate the polymerization in case of nickel acetylacetonate. The reaction products are characterized as poly‐Schiff bases. Upon treatment with acid the polymers of primary alkyl isocyanides rearrange to polycyanides.
Studies on polypeptides xiv synthesis of possible rennin substrates
Authors: Schattenkerk Cecile , Voskuyl‐Holtkamp Ingrid , Bokhorst Ria 
Published: September 2010

AbstractLeu‐Ser‐Phe‐Met‐Ala‐Ile‐Pro‐Pro‐Lys‐Lys and 14 smaller peptide fragments simulating increasing parts of the sequence around the rennin sensitive Phe‐Met bond in k‐casein have been synthesized and characterized.
On the mechanism of the amination of 4‐bromo‐2,6‐diphenyl‐ and 4,5‐dibromo‐2,6‐diphenyl‐pyrimidine with potassium amide in liquid ammonia
Authors: de Valk J. , van der Plas H. C. 
Published: September 2010

AbstractIt has been found that the amination of 4‐bromo‐2,6‐diphenylpyrimidine into the corresponding 4‐amino compound with potassium amide in liquid ammonia at −33° does not occur by the ANRORC‐mechanism but by an EA and/or AE‐mechanism. Treatment of 4,5‐dibromo‐2,6‐diphenylpyrimidine with potassium amide under the above‐mentioned conditions leads to a mixture of 4‐amino‐5‐bromo‐2,6‐diphenylpyrimidine and 4‐amino‐2,6‐diphenylpyrimidine. Evidence is presented that in the formation of 4‐amino‐5‐bromo‐2,6‐diphenylpyrimidine the ANRORC‐mechanism is operative to the extent of about 20%. The synthesis of the 1(3)‐15N‐enriched 4‐bromo‐2,6‐diphenyl‐ and the 4,5‐dibromo‐2,6‐diphenyl‐pyrimidine is described.
The crystal structure of 8‐methoxy‐N‐tosyl‐3‐trichloromethyl‐2,3,4,4a,5,6‐hexahydrobenzo[f]quinoline
Authors: van der Meer H. 
Published: September 2010

AbstractThis compound crystallizes in space group P21/c with cell constants a = 13.968, b = 19.395, c = 16.575, β = 90.37°, Z = 8. The crystal structure was determined in order to check the interpretation of NMR‐spectra.
Homogeneous hydrogenation of substituted cis‐cinnamic acids with pentacyanocobaltate(II); kinetics and mechanism
Authors: Basters J. , Groenenboom C. J. , van Bekkum H. , van Reijen L. L. 
Published: September 2010

AbstractThe homogeneous hydrogenation and deuteration with pentacyanocobaltate(II) of a series of substituted cis‐cinnamic acids have been investigated. During the hydrogenation partial isomerization to the corresponding trans‐isomers was observed. In the deuterations the labelling of the intermediate trans‐compounds ‐ as determined with PMR spectroscopy ‐ revealed that in cis‐cinnamic acids the first hydrogen transfer takes place at the α‐carbon atom. On the basis of effects of ortho‐substituents, isotope effects and deuterium labelling it is suggested that in trans‐cinnamic acids the initial hydrogen transfer takes place at the β‐carbon atom.
Molybdenum‐catalysed epoxidation of olefins with alkyl hydroperoxides I. Kinetic and product studies
Authors: Sheldon R. A. 
Published: September 2010

AbstractIn the homogeneous molybdenum‐catalysed epoxidation of olefins bytert‐alkyl hydroperoxides two competing processes, epoxidation and hydroperoxide decomposition, have been delineated.Hydroperoxide decomposition involves free‐radical reactions initiated by electron‐transfer reactions of Mo(V) and Mo(VI) complexes with the hydroperoxide. The rates and products of hydroperoxide decomposition are dependent on the solvent and the presence or absence of an olefin.The rate of epoxidation depends on the structure of the olefin and, after an initial period during which the rate changes, it becomes independent of the structure of the molybdenum compound originally added as the catalyst. The active catalyst in the epoxidation reaction is a molybdenum(VI) compound. The active epoxidizing agent is most likely a complex of molybdenum(VI) with the hydroperoxide, which transfers an oxygen atom to the olefin via a cyclic transition state analogous to that for the epoxidation of olefins with organic peracids.
Nouveaux oxamétallocycloalcanes (VII) Synthèse de (germa‐, sila‐, et stanna‐)dioxacycloalcanes et alcènes par insertion de dérivés carbonylés sur la liaison métal‐oxygène d'éthers cycliques organométalliques
Authors: Barrau J. , Massol M. , Mesnard D. , Satgé J. 
Published: September 2010

AbstractThe insertion reactions of carbonyl derivatives such as acetaldehyde, chloral, hexachloro‐ and hexafluoro‐acetone on the metal‐oxygen bond of alkoxy‐organometallic compounds have been studied in the case of numerous cyclic ethers containing silicon, germanium or tin atoms in the ring.These reactions proceed by ring expansion leading to the formation of cyclic acetals: germaoxetanes yield 4‐germa‐1,3‐dioxanes, (sila‐, germa‐ or stanna‐) oxacyclopentanes give 1,3‐dioxacycloheptanes and (germa‐ or stanna‐) oxacyclopentenes lead to 1,3‐dioxacycloheptenes with the group IV element in position 4.The mechanism of these insertion reactions is discussed according to the nature of carbonyl derivatives and metal heteroatom in the starting cyclic compounds, as well as catalytic and solvent effects.
The crystal and molecular structure of propenyl p‐tolyl sulfone
Authors: Klazinga A. H. , Vos Aafje 
Published: September 2010

AbstractAn X‐ray diffraction study of propenyl p‐tolyl sulfone has shown that the S‐CH = CH‐CH3 group has the trans configuration rather than the cis configuration assumed by Backer, Strating and Drenth.
Enolization and oxidation III. Ferrocene Catalyzed Autoxidation of 3‐Hydroxybutan‐2‐one in an Acidic Medium
Authors: Lubach J. , Drenth W. 
Published: September 2010

AbstractThe autoxidation of 3‐hydroxybutan‐2‐one is studied in acidic 50 vol. % aqueous ethanol. The reaction is catalyzed by ferrocene. The rate determining step of the ferrocene catalyzed reaction is the acid catalyzed enolization of the substrate. Subsequently, both the enol‐form of the substrate and ferrocene are oxidized by oxygen.
Force fields for the vinyl halides
Authors: Elst R. , Rogge W. , Oskam A. 
Published: September 2010

AbstractNormal coordinate calculations of vinyl fluoride, chloride, bromide and iodide are reviewed. Modified Valence Force Fields are reported, by making use of published vibrational data of all deuterated isotopic species and observed Coriolis constants. The iterative least‐squares procedure used adjusts observed and calculated frequencies and second order Coriolis constants simultaneously, so we introduced a mutual dependency between the two vibrational species A′ and A″.Our calculations suggest frequency reassignments for some isotopic molecules.
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (XXX) Reaction of chlorophenyl‐ and chlorodiphenyl‐pyrazines with potassium amide in liquid ammonia
Authors: Lont P. J. , van der Plas H. C. 
Published: September 2010

AbstractWhile treatment of 2‐chloro‐3‐phenylpyrazine with potassium amide in liquid ammonia yields only 2‐amino‐3‐phenylpyrazine, from 2‐chloro‐6‐phenylpyrazine on the contrary two ring contraction products, 4(5)‐phenylimidazole and 2‐cyano‐4(5)‐phenylimidazole are obtained. From 2‐chloro‐5‐phenylpyrazine a mixture of 2‐amino‐5‐phenylpyrazine, 4(5)‐phenylimidazole as well as 2‐cyano‐4(5)‐phenylimidazole is formed.In the diphenyl series it has been established that, whereas 2‐chloro‐3,5‐diphenylpyrazine gives only the corresponding 2‐aminopyrazine, 2‐chloro‐ 5,6‐diphenylpyrazine gives a mixture of the amino product and two ring contraction products: 4,5‐diphenylimidazole and 2‐cyano‐4,5‐diphenylimidazole.2‐Chloro‐3,6‐diphenylpyrazine was found to be relatively inactive towards potassium amide in liquid ammonia.This divergent behaviour is explained by the high susceptibility of the positions 3 and 6 of the 2‐chloropyrazine for a nucleophilic attack as established by 14C‐ and 15N‐labelling studies which were made previously.
The reaction of 4‐chloroquinazoline with lithium piperidide in piperidine and potassium amide in liquid ammonia at −75°
Authors: de Valk J. , van der Plas H. C. , Jansen F. , Koudijs A. 
Published: September 2010

AbstractTreatment of 4‐chloroquinazoline with lithium piperidide in piperidine at −75° yields a mixture of a stable open chain compound i.e. o‐(piperidinomethylene)iminobenzonitrile and the corresponding 4‐piperidino compound. When 4‐chloroquinazoline is aminated with potassium amide in liquid ammonia at −75° only 4‐aminoquinazoline is formed. By means of 15N‐labelling it has been shown that about 50% of the 4‐aminoquinazoline is formed via an ANRORC mechanism. The synthesis of 4‐chloro‐[3‐15N]quinazoline is described.
On the repetitive excess mixed anhydride method for the synthesis of peptides. Synthesis of the sequence 1‐10 of human growth hormone
Authors: Beyerman H.C. , de Leer E.W.B. , Floor J. 
Published: September 2010

AbstractThe synthesis of the fully protected N‐terminal decapeptide of human growth hormone, Boc‐Phe‐Pro‐Thr(Bzl)‐Ile‐Pro‐Leu‐Ser(Bzl)‐Arg(NO2)‐Leu‐Phe‐OMe (HGH 1‐10) by the repetitive excess mixed anhydride (REMA) method is described.Starting from Phe‐OMe this sequence was synthesized in a stepwise manner in an overall yield of 59%. In the coupling of Boc‐Ile to Pro‐Leu‐Ser(Bzl)‐Arg‐(NO2)‐Leu‐Phe‐OMe the isobutoxycarbonyl derivative of the amino‐component was isolated. This problem of reaction on the undesirable side of the mixed anhydride in the couplings to proline‐peptides was circumvented by the coupling of dipeptides, viz. Boc‐Ile‐Pro and Boc‐Phe‐Pro. Also a larger peptide fragment, ZPhe‐Pro‐Thr‐Ile‐Pro (HGH 1‐5), was conveniently coupled to the C‐terminal pentapeptide. Synthesis of Boc‐Leu‐Ser(Bzl)‐Arg(NO2)‐Leu‐Phe‐OMe (HGH 6‐10) was performed with and without intermediate purification. It was found that the yield was higher when no purifications were applied.HGH 6‐10 was compared with the corresponding peptide synthesized by the solid phase method. Both products were found to be identical with regard to melting point, optical rotation and chromatographic behaviour. The decapeptide, on deprotection, showed identical chromatographic behaviour with a product obtained by the solid phase method. The optical rotations showed a small difference; no significant racemization could be detected on digestion with L‐amino‐acid oxidase.
Kinetics and mechanism of primary cracking reactions in thermal high pressure hydrogenolysis of tetralin and indan. Part I
Authors: Penninger J.M.L. , Slotboom H.W. 
Published: September 2010

AbstractKinetics of the primary cracking reactions occurring in the high pressure thermal hydrogenolysis of 1, 2, 3, 4‐tetrahydronaphthalene (tetralin) and hydrindene (indan) were studied in a flow reactor at temperatures from 460° to 540°C, total pressures from 10 to 160 atm. and molar ratios of hydrogen‐to‐hydrocarbon from 2 to 100.As primary cracking products from tetralin were identified n‐butylbenzene, styrene, ethylene, 1‐methylindan and o‐propyltoluene.From indan were obtained n‐propylbenzene, toluene, ethylene, o‐ethyl‐toluene, o‐xylene and methane.Chain mechanisms are proposed for the reactions leading to these primary products.The theoretical rate equations derived from these are in good agreement with experimental results.
A novel type of catalysis of the [2 + 2] cycloaddition of cyclopropenes
Authors: Schipperijn A.J. , Lukas J. 
Published: September 2010

AbstractIn the presence of zeolites, cyclopropenes can cyclodimerize to give tricyclo‐[3.1.0.02,4]hexanes, isomerize to yield 1,3‐butadienes or polymerize. Which pathway is chosen depends on the structure of the cyclopropene and on the nature of the zeolite. This novel method for the cyclodimerization of cyclopropenes is superior to known procedures of preparing tricyclohexanes. It constitutes a unique example of a reaction being forced to proceed in a certain direction by spatial restriction of the reacting molecules.
Ketene formation from aliphatic ketones in a silent electrical discharge
Authors: van Drumpt J. D. , Mackor A. 
Published: September 2010

AbstractThe title reaction in the plasma of a silent electrical discharge at 40° is described. Acetone, ethyl methyl ketone, diethyl ketone and diisopropyl ketone all give rise to the formation of ketenes. From these ketones not only is the corresponding ketene formed, but the lower ketenes also, presumably by degradation of the higher ketenes in the plasma of the discharge. Acetic acid also gives rise to ketene formation. In contrast to the comparable thermal reactions, total ketene yields for the ketones are all of the same order of magnitude. With acetone and acetic acid the energy yields for ketene formation are better for the discharge than for the thermal reaction.