bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sulfenylated cyclic β‐keto esters and cyclic β‐diketones; synthesis and reactions with nucleophiles
Authors: de Groot Ae. , Jansen B. J. M. 
Published: September 2010

AbstractQuenching the enolates of cyclic β‐diketones or 2‐oxocycloalkanecarboxylates with phenylsulfenyl chloride or methylsulfenyl chloride produces the corresponding x‐sulfenylated products. Nucleophilic attack on these x‐sulfenylated 1,3‐dicarbonyl compounds produces regiospecific sulfenylated linear dicarboxylic acids, acid esters, diesters or oxo esters suitable for further chemical transformation, this has been demonstrated in the synthesis of the queen substance of the honoy bee. In some cases recyclization of the intermediate enolates was observed to regiospecific sulfenylated cyclohexenones.
Solid compounds of dibromo(N,N‐di‐n‐butyldithiocarbamato)gold(III) with trans‐Stilbene, trans‐azobenzene and trans,trans‐1,4‐diphenyl‐1,3‐butadiene. Crystal structure determinations of [Br2AuS2CN(C4H9)2)2·C6H5(CH)2C6H5 and [Br2AuS2CN(C4H9)2]·C6H5(CH)4C6H5
Authors: Wijnhoven F. T H. H. M. , Bosman W. P. , Willemse J. , Cras J. A. 
Published: September 2010

AbstractBr2Au(Bu2dtc) forms solid compounds with trans‐stilbene, trans‐azobenzene, trans,trans‐1,4‐diphenyl‐1,3‐butadiene, tolane and dibenzyl, of formula [Br2Au(Bu2dtc)]2·organic component. The crystal structures of the title compounds are solved. No specific interactions between the dithiocarbamato compound and the organic component are observed.
Analysis of cocaine, pseudococaine, allococaine and allopseudococaine by ion‐pair reverse‐phase high‐performance liquid chromatography
Authors: Olieman C. , Maat L. , Beyerman H. C. 
Published: September 2010

AbstractThe title compounds can be separated by liquid chromatography on a column of octadecylsilyl‐silica with the addition to the eluent of n‐heptanesulfonate and identified by peak area measurements at different UV wavelengths.
Relation entre la configuration et la tautomérie de formyl‐hydrazino‐5 as‐triazines
Authors: Daunis J. , Follet M. , Gelize M. 
Published: September 2010

AbstractL'étude de la configuration E ou Z de formyl‐hydrazino as‐triazines, établie par RMN et par le calcul théorique, permet de déterminer la structure tautomère de ces composés: de type tétrahydro‐2,3,4,5 triazine ou dihydro‐2,5 triazine selon la nature des substituants.
A note on the hydrobromination of 1‐alkenes in the presence of zeolites
Authors: Wortel Th. M. , Rozendaal S. , van Bekkum H. 
Published: September 2010

AbstractThe zeolite‐catalyzed hydrobromination of 1‐alkenes was investigated. Contrary to literature data, normal (Markovnikov) addition of hydrogen bromide yielding 2‐bromoalkanes was observed if peroxide impurities were removed thoroughly from the reactants. Substantial amounts of 3‐ and 4‐bromoalkanes were formed due to zeolite‐catalyzed isomerization of the alkene.
Preliminary Communications: Chemistry of 2H‐thiopyran and derivatives V. Regiospecific methylation and protonation of the di‐anion, obtained from reductive cleavage of 2H‐thiopyran
Authors: Gräting R. , Brandsma L. 
Published: September 2010

AbstractReductive cleavage of 2H‐thiopyran 1 with naphthylsodium or sodium in THF or THF/HMPT mixtures, respectively, gives the di‐anion magnified image, which is protonated and methylated by the first equivalent of methyl iodide on the terminal carbon atom.
The enhancement by visible light of the catalytic activity of Co(II)‐tetrasulphophthalocyanine on the oxidation of mercapto‐ethanol
Authors: Beelen T. P. M. , Da Costa Gomez C. O. , Kuijer M. 
Published: September 2010

AbstractThe rate of the selective oxidation of mercaptoethanol by dioxygen to disulphide, catalysed by Co(II)‐tetrasulphophthalocyanine, is enhanced with a factor 2 à 4 by irradiation with light in the range of 600‐700 nm. This effect can be ascribed to the conversion of dimers of Co(II)‐tetrasulphophthalocyanine to catalytically active monomers.
The role of tetraalkylammonium salts in the electro‐reduction of ketones. Part II: The reduction of acetophenone in an aprotic environment
Authors: van Tilborg W. J. M. , Smit C. J. , van Santen R. A. 
Published: September 2010

AbstractA polarographic study of the electro‐reduction of acetophenone in dry acetonitrile has revealed that under strictly anhydrous conditions the carbonyl compound can be reduced only if tetraalkylammonium ions are present. The role played by these ammonium ions is discussed. It is concluded that the catalytic effect of the ammonium ions has to be related to an increased polarization of the carbonyl double bond being induced during collision of the ammonium ions with the carbonyl compound. At high ammonium ion concentrations, however, the effect of this catalysis becomes smaller due to preferential adsorption of the ammonium ions on the electrode surface, as a result of which the carbonyl compound is displaced from the direct vicinity of the electrode.
Formation of γ‐lactones by boron trifluoride‐catalysed ring closure of quinoid γ‐oxo‐α,β‐unsaturated carboxamides. Structure and reaction mechanism
Authors: Verboom W. , Bos H.J.T. 
Published: September 2010

AbstractTreatment of the quinoid N,N‐dialkyl‐α‐(3,5di‐tert‐butyl‐2‐oxo‐3,5‐cyclohexadienylidene)‐α‐phenylacetamides 6 with boron trifluoride etherate generally gives rise to rearrangement into the γ‐lactones 3‐dialkylamino‐5,7‐di‐tert‐butyl‐3‐phenyl‐2,3‐dihydrobenzo[b]furan‐2‐ones 11. In the case of the carboxamide 7, N,N‐diethyl‐α‐(3,5‐di‐tert‐butyl‐6‐hydroxyphenyl)‐α‐oxoacetamide 14 is formed. The quinoid N,N‐diethyl‐α‐methylthio‐α‐(10,oxo‐9‐phenanthrenylidene)acetamide 8 is converted by boron trifluoride etherate into the γ‐lactone 3,3‐bis(methylthio)‐2,3‐dihydrophenanthro‐[9,10‐b]furan‐2‐one 22 and phenanthro[9,10‐b]furan‐2,3‐dione 23. In the presence of alcohols, intermediate carbocations are generally trapped; non‐fully aromatic phenanthrene derivatives are sometimes formed.
Chemistry of electron‐rich conjugated polyenes V. Regio‐ and stereo‐selectivity in Diels‐Alder reactions of 1‐alkoxy‐1,3‐butadienes and β‐cyanostyrenes
Authors: Broekhuis A. A. , Scheeren J. W. , Nivard R. J. F. 
Published: September 2010

AbstractEffects of substituents in diene and dienophile on the regio‐ and stereo‐selectivity of Diels‐Alder reactions have been studied on cycloadditions of alkoxy‐substituted 1,3‐butadienes (1) and 2‐substituted cyanoethenes (2). The regioselectivity is always very high, and is determined by the magnitude of the orbital coefficients of the interacting carbon atoms according to the frontier orbital theory. The stereoselectivity is more determined by steric factors than by secondary orbital overlap. The results point to a transition state, in which the planes of diene and dienophile, are non‐parallel (Figure 1).
Potential carcinostatics V. Synthesis and properties of potential inhibitors of the adenylosuccinate synthetase and adenylosuccinate lyase system
Authors: Wanner M. J. , van Wijk E. M. , Koomen G. J. , Pandit U. K. 
Published: September 2010

Abstractβ,β‐Dimethylaspartic acid was obtained by the aluminium‐amalgam reduction of the O‐methyloxime of diethyl 2‐oxo‐3,3‐dimethyl‐1,4‐butanedioate and subsequent hydrolysis. The (latter) diester was conveniently prepared by the condensation of ethyl 2‐bromo‐2‐methylpropionate with diethyl oxalate, under the influence of magnesium. β,β‐Difluoroaspartic acid, threo β‐methylaspartic acid and β,β‐dimethylaspartic acid (as racemates) were coupled with 6‐chloropurin‐9‐yl riboside to yield the corresponding nucleosides. The bases methyl 7‐oxo‐7H‐pyrido[2.1‐i]purine‐9‐carboxylate and 6‐[2,3‐bis(methoxycarbonyl)propyl]purine were converted into the corresponding nucleosides by coupling with O2,O3,O5‐tribenzoylribofuranosyl chloride and removal of the protecting groups. The biological test results on leukemia P‐388 are presented.
(2 + 2)‐Cycloaddition of o‐quinones to N,N‐dialkyl‐3‐alken‐1‐ynyl‐1‐amines. Thermal or photochemical ring closure of the adducts to 2H‐1‐benzopyran derivatives
Authors: Verboom W. , George A. V. E. , Brandsma L. , Bos H. J. T. 
Published: September 2010

AbstractAddition of 9,10‐phenanthrenequinone or 3,5‐di‐tert‐butyl‐o‐benzoquinone to N,N‐dialkyl‐3‐alken‐1‐ynyl‐1‐amines R2‐CHCH‐C≡C‐NR12 (4) gives quinoid α‐alkenyl‐γ‐oxo‐α,β‐unsaturated carboxamides 6 or 8, respectively; these undergo a spontaneous ring‐closure, or can be cyclised photochemically into 2H‐phenanthro[9,10‐b]pyran‐4‐carboxamides 7 or 2H‐1‐benzopyran‐4‐carboxamides 9.
Addition/elimination reactions of an α‐tosyl substituted sulfine with nucleophilic reagents
Authors: van der Leij M. , Strijtveen H. J. M. , Zwanenburg B. 
Published: September 2010

AbstractOxidation of methyl 2‐methyl‐2‐p‐(tolylsulfonyl)propanedithioate with m‐chloroperbenzoic acid furnished the corresponding sulfine p‐MeC6H4SO2CMe2C(SO)SMe (2). This sulfine that bears a leaving group at its α‐carbon atom has especially been designed to investigate the possibility of a thiophilic addition with a concurrent elimination reaction upon treatment with nucleophilic reagents. Attempts to prepare the sulfine p‐MeC6H4SO2CMe2C(SO)Ph were unsuccessful. Reaction of sulfine 2 with MeOH/Et3N (or EtOH/Et3N) gave α‐methylthio‐α,β‐unsaturated sulfinates Me2CC(SMe)S(O)OMe (or Et) (10, 11). α‐Functionalized carbanions (α‐sulfonyl, α‐oxo or α‐cyano) also gave an addition‐elimination reaction to produce ketene dithioacetal monoxide derivatives (15–17). Similar products were obtained upon treatment with PhMgBr, PhCH2MgBr or MeLi. Evidence is presented that the thiophilic addition and the elimination of sulfinate take place synchronously.
Sulphur participation in cyclization reactions
Authors: de Loos Walter A. J. , van den Berg‐van Kuijk Anne J. W. , van Iersel Hans M. , de Haan Jan W. , Buck Henk M. 
Published: September 2010

AbstractCyclization initiated by thiiranium ions was investigated. Cis‐fused decalins were formed by a process involving inversion. In nitromethane a sulphonium salt 8 was formed. The reactions of 8 with nucleophilic reagent deviated from those of comparable compounds. It is expected that a product‐controlled transition state accounts for this feature.
Synthesis of fragments of human β‐lipotropin, βh‐LPH. Part III. The synthesis of des‐1‐tyrosine‐γ‐endorphin, i.e. β‐LPH‐(62‐77)
Authors: Greven H. M. , Bijl W. A. A. J. , van Nispen J. W. 
Published: September 2010

AbstractThe synthesis of the hexadecapeptide des‐1‐tyrosine‐γ‐endorphin, i.e. β‐LPH‐(62‐77), by means of the fragment condensation approach, is described. According to De Wied and co‐workers, this peptide, or a closely related one, may function as an endogenous neuroleptic.
A simple approach to 12‐azaprostaglandin congeners
Authors: Armande J. C. Lapierre , Pandit U. K. 
Published: September 2010

AbstractThe base‐catalyzed alkylation of N‐acylated 3‐pyrrolines has been studied. The reaction has been utilized in an approach to the synthesis of 12‐azaprostaglandins according to the following sequence. 3‐Pyrroline was acylated with 1‐chloro‐1‐octen‐3‐one and the resulting amide alkylated at the 2‐position with I‐(CH2)6C(OCH3)3. Subsequently, the α‐ and β‐(13,14‐dihydro)‐prostanoid chains were formed by sodium borohydride reduction, followed by hydrolysis. The resulting product, 1‐(3‐hydroxyoctyl)‐2‐(6‐methoxycarbonylhexyl)‐3‐pyrroline (13), constitutes a central intermediate for 12‐azaprostaglandins.
The photosensitized oxidation of a 19‐norsteroid: 11 β‐chloro‐17α‐19‐norpregn‐4‐en‐20‐yn‐17‐ol
Authors: Schönemann K. H. , van Vliet N. P. , Zeelen F. J. 
Published: September 2010

AbstractPhotosensitized oxygenation of 11β‐chloro‐17α‐19‐norpregn‐4‐en‐20‐yn‐17‐ol yields, aft́er reduction of the initially formed hydroperoxides, 11β‐chloro‐17α‐19‐norpregn‐3‐en‐20‐yne‐5α,17‐diol as the major product and 11β‐chloro‐17α‐19‐norpregn‐5‐en‐20‐yne‐4β,17‐diol as a minor product.
Photochemical hydroxylation of 7,8‐dimethylalloxazine (lumichrome). Structure elucidation of the irradiation product
Authors: te Nijenhuis B. , Mulder A. C. , Berends W. 
Published: September 2010

AbstractThe synthesis of 8‐methoxy‐3‐(methoxycarbonyl)‐6,7‐dimethyl‐2‐(methylamino)quinoxaline is described. The synthesized compound appeared to be identical with the product obtained by degradation of the irradiation product of lumichrome. From this the conclusion is drawn that the irradiation product of lumichrome in water is 9‐hydroxylumichrome.
The molecular structure of 6‐(bromomethyl)‐1,2,4‐trichloro‐3‐ethoxy‐3,7,7‐trimethoxybicyclo[2.2.1] heptane; an X‐ray study
Authors: Lenstra A. T. H. , van de Mieroop W. , Geise H. J. , van Bree J. , Anteunis M. 
Published: September 2010

AbstractHydrolysis of 6‐(bromomethyl)‐ 1,2,4‐trichloro‐3,7,7‐trimethoxybicyclo[2.2.1] hept‐2‐ene with perchloric acid in aqueous ethanol yields inter alia the title compound. X‐ray analysis proved the positioning of the substituents to be 6‐endo‐(bromomethyl)‐2‐endo‐chloro,3‐endo‐ethoxy, which is evidence that the addition in this case follows an endo‐tram mechanism.The title compound crystallizes in the monoclinic space group P21/n with a = 10.504 Å, b = 10.507 Å, c = 15.783 Å, γ = 92.20° and Z = 4. The structure was solved by conventional techniques to an R = 0.063 using Mo(Zr) diffractometer data. The effect of the substitution on the conformation of the norbornane skeleton is discussed, as well as the geometry of the acetal groups in terms of the anomeric effect.
MCSCF and CI calculations of the dipole moment of cyclopropene
Authors: van Lenthe Joop H. , Smits Jos L. M. 
Published: September 2010

AbstractHartree‐Fock calculations lead to a dipole moment of cyclopropene opposite to that derived from experiments. We present MCSCF and CI calculations performed on a split valence basis set level in order to investigate the influence of correlation. Since the MCSCF and CI results scarcely differ from the Hartree‐Fock results, we conclude that the theoretically assigned polarity is the correct one.
Conformational equilibria of 3‐(cis‐styryl)phenanthrene and some benzologues
Authors: Somers J. B. M. , Laarhoven W. H. 
Published: September 2010

AbstractAn NMR investigation of cis and trans isomers of styrylphenanthrene and some benzologues was performed, in which Δtrans‐cis values (δtrans‐δcis), temperature dependence (ΔT) in CS2 and ASIS effects were determined. It was concluded that in the series styryl‐phenanthrene (2),‐benzo[c]‐phenanthrene (1),‐dibenzo[c,g]triphenylene (10),‐hexahelicene (9) only 1 exists mainly as a cis‐synrotamer, whereas in the other compounds the cis‐anti rotamer predominates in varying degrees. The introduction of an additional benzo group in 1 and 2 at the ring, containing the styryl substituent, which leads to the styryl‐chrysene (11) and styryl‐benzo[c]chrysene (12), shifts the conformational equilibrium to the cis‐syn rotamer. The introduction of polar substituents at the para‐position of 2‐styrylbenzo[c]phenanthrene has only a small influence on the syn‐anti equilibrium. The observed effects are discussed.
An interesting substituent effect on the acid‐catalyzed skeletal rearrangement of seco‐homocubanes
Authors: Vankan J. M. J. , Klunder A. J. H. , Noordik J. H. , Zwanenburg B. 
Published: September 2010

AbstractThe acid catalyzed rearrangement of 1‐bromotetracyclo[4.3.0.02.503.8]nonan‐4‐one 1b has been studied. With aqueous HBr, the exclusive formation of 2,7‐dibromotricyclo[4.2.1.03.7]‐nonan‐4‐one 4b was observed. This structure was established by X‐ray analysis. The divergency in behaviour of seco‐homocubane 1b and its 9‐ethylene acetal derivative 1a towards acidic reagents reveals a directing effect of the 9‐ethylene acetal function on the skeletal rearrangement.
C‐Nitroso compounds. Part XXXIII. Reaction of α‐chloronitrosoadamantane with Grignard reagents
Authors: Schenk C. , Beekes M. L. , de Boer Th. J. 
Published: September 2010

AbstractThe reaction of α‐chloronitrosoalkanes with aliphatic and aromatic Grignard reagents RMgX has been studied using the model compound α‐chloronitrosoadamantane (AdClNO)1. In addition to adamantanone oxime 7 (4‐60%) and the adamantanone oxime ether 8 (trace −28%), the expected nitrone 2 is formed. The nitrone can be isolated for synthetic purposes using a non‐ chromatographic procedure in widely varying yields ( 6 87 %). The structure of all nitrones has been determined using spectroscopic techniques.Formation of oxime and oxime ether has been explained with the mechanism outlined in Scheme 3. This also accounts for the drastic changes in product distribution with the nature of the Grignard reagent. The mechanism involves nitrone formation via polar 1,2‐addition of the Grignard reagent to the nitroso group, and single electron transfer (SET) from the Grignard reagent to the nitroso compound which leads to an iminoxy radical together with radical R*. The latter combines with the multident iminoxy radical on nitrogen and oxygen (not on carbon) producing the nitrone and the oxime ether. Disproportionation can result in the formation of oxime. The oxime can also be formed when iminoxy radicals accept an electron from the Grignard reagent.As the electron donating power is strongly influenced by the nature of the Grignard reagent (i.e. SET vs. polar addition), widely varying product distributions are obtained. The phenyl Grignard reagent is amongst the poorest of electron donors, and therefore gives almost exclusively nitrone by polar 1,2‐addition.Since nitroso compounds are normally excellent free radical scavengers, it is difficult to explain why trapping of transient radicals R* by the nitroso compound, followed by loss of halogen, appears to be relatively unimportant as a route to nitrone (Scheme 3, reaction iii). The formation of dibenzyl (42%) from the reaction of AdClNO 1 with benzylmagnesium bromide is equally remarkable.
Recherches en série triazépine XVI.Condensation des composés β‐dicarbonylés avec les thiosemicarbazides
Authors: Hasnaoui A. , Lavergne J.‐P. , Viallefont Ph. 
Published: September 2010

AbstractCondensations of β‐dicarbonyl compounds with thiosemicarbazide and 1‐ and 2‐methylthiosemicarbazide give three types of heterocyclic compounds. Depending upon the reagents and experimental conditions, triazepinones, triazepines, 1,2,4‐triazolines or pyrazoles are formed. Mechanisms explaining these cyclisations are proposed.
A convenient synthesis of specifically substituted conjugated dienes via organocopper(I) induced SN2′ reactions. An attractive route to myrcene
Authors: Kleijn H. , Westmijze H. , Meijer J. , Vermeer P. 
Published: September 2010

AbstractThe paper describes the preparation of a number of symmetrically substituted 1,3‐dienes H2C=C(R)‐C(R)=CH2 (3a‐d) as well as non‐symmetrically substituted 1,3‐dienes H2C=C(R1)‐C(R)=CR2R3 (3e‐i, R ≠ R1) by means of organocuprate induced SN2′ reactions in the esters X‐CH2‐C≡C‐CH2‐X (1, X = MeS(O)O or ToS‐O) and MeS(O)‐O‐CH2‐C(R1)=C=CR2R3 (4) respectively. An attractive application of the method is the easy preparation of the natural compound myrcene from 4 in which R1, R2 and R3 are hydrogen. A mechanistic rational for the reactions is discussed.
Studies on polypeptides XXXIII: Semisynthetic Ribonuclease analogues. The role of histidine‐119
Authors: Serdijn J. , Hoes C. , Raap J. , Kerling K. E. T. 
Published: September 2010

AbstractAs part of a structure‐activity relationship study of ribonuclease, focussing on the role of histidine‐119 in the active centre, two tetradecapeptides were synthesized by the solid‐phase method: [His119]RNase 111‐124 and the corresponding analogue in which His‐119 is replaced byL homohistidine.While the [Hhis119] analogue has almost the same binding capacity towards RNase 1‐118 protein as the natural peptide, the resulting complex is devoid of any catalytic activity when RNA or 2′,3′‐CMP is used as substrate.
Synthesis of racemic 3‐hydroxy‐N‐methyl‐6‐oxomorphinan (Chemistry of opium alkaloids, Part XIV)
Authors: Olieman C. , Nagelhout Ph. , de Groot A. D. , Maat L. , Beyerman H. C. 
Published: September 2010

AbstractThe preparation of racemic 3‐hydroxy‐N‐methyl‐6‐oxomorphinan (5) by acid‐catalysed cyclization of 1‐(4‐hydroxybenzyl)‐1,2,3,4,5,8‐hexahydro‐6‐methoxy‐2‐methylisoquinoline (4) and its 4′‐methyl ether 6 is described. The corresponding N‐formyl derivatives did not give the desired cyclization.
ZnCl2‐catalysed cycloadditions between ketene acetals and α,β‐unsaturated carbonyl compounds. A simple route to 2,2‐dialkoxy‐3,4‐dihydropyrans
Authors: Bakker C. G. , Scheeren J. W. , Nivard R. J. F. 
Published: September 2010

Abstract2,2‐Dialkoxy‐3,4‐dihydropyrans (3) can be obtained under mild conditions and in good yields from ketene acetals (1) and α,β‐unsaturated carbonyl compounds (2) in the presence of ZnCl2. At low temperatures (< −20°C) the reaction between1and2proceeds as a (2 + 2)‐cycloaddition, leading to an oxetane (4), which can sometimes be isolated by neutralisation of the Lewis acid. At higher temperatures, however, the oxetanes decompose into the starting compounds, eventually leading to the thermodynamically more stable dihydropyrans. The cycloadditions of tetramethoxyethene (1a) with2, having no substituents at the β‐carbon atom, yield a cyclobutane derivative as the low temperature product; in cycloadditions of α,β‐unsaturated esters this is the final product. Cycloadditions of 2‐chloroketene acetal (1e) lead in some cases to 2:1 adducts. The deviating behaviour of1aand1eis discussed.
Transthallation of anisole and chlorobenzene by phenylthallium(III) bis(trifluoroacetate)
Authors: Kooyman E. C. , Huygens A. V. , de Lepper J. P. J. , de Vos D. , Wolters J. 
Published: September 2010

AbstractPhenylthallium(III) bis(trifluoroacetate) (PhTlX2) reacts with excess of anisole at 70‐80°, yielding mainly the three isomeric anisylphenylthallium(III) compounds (o‐, m‐, p‐AnPhTlX). Monoanisylthallium(III) derivatives (o‐, m‐, p‐AnTlX2) are obtained only in the presence of excess of HX. The slow transthallation reaction of chlorobenzene requiring the presence of HX leads to the o‐, m‐, p‐ClC6H4TlX2 isomers rather than to diarylthallium(III) compounds. The three isomeric anisylphenylthallium(III) compounds (o‐, m‐, p‐AnPhTlX) readily undergo exchange and isomerization reactions with anisole in the presence ‐ or more slowly in the absence ‐ of HX. Similar processes were observed with chlorobenzene but only in the presence of HX. (p‐Chlorophenyl)phenylthallium(III) trifluoroacetate is much less reactive, both towards anisole and chlorobenzene. With long reaction times the systems approach equilibrium distributions, which are approximately the same as those found for the prolonged direct thallation of the aromatic compounds. Tentative mechanistic interpretations include three different modes of formation of arylthallium bonds and draw a parallel between thallation, mercuration and plumbylation.
Empirical force field calculations VIII The interconversion of all‐cis‐1,2,3,4,5,6‐hexamethylcyclohexane
Authors: van de Graaf B. , Baas J. M. A. , Widya H. A. 
Published: September 2010

AbstractThe calculation of the enthalpy of activation for the interconversion of the equi‐energetic chair conformers of all‐cis‐1,2,3,4,5,6‐hexamethylcyclohexane (1), using five empirical force fields, gives rather poor results. A sizable negative entropy of activation, indicated by the calculations, can only partly compensate for the differences between experimental and calculated values of the free enthalpy of activation. Comparison of individual strain components with similar data for cyclohexane indicates the importance of the non‐bonded interactions for the interconversion barrier. The barriers for the chair‐chair interconversions of cyclohexane and 1 should be included in future force field parametrizations.