bluuebunny/crossref_metadata_2025 huggingface dataset:
The chemistry of small ring compounds. Part 36 CIDNP effects during the oxidation of substituted cyclopropanone methyl hemiacetals by di‐tert‐butyl diperoxyoxalate
Authors: Bakker B. H. , Bok Th. Reints , Steinberg H. , de Boer Th. J.
Published: September 2010

The reaction of tetramethylcyclopropanone methyl hemiacetal (2) and phenylcyclopropanone methyl hemiacetal (7) with di‐tert‐butyl diperoxyoxalate (TBPO) has been studied in connection with observed CIDNP effects. Oxidation of these hemiacetals by tert‐butoxyl radicals (generated from TBPO) gives rise to the ring‐opened radical Me2 •CCMe2COOMe (3) and C6H5•CHCH2COOMe (8) respectively. The existence of radical 3 is clearly demonstrated in benzene solution by the observed A/E multiplet effect for the disproportionation products HCMe2CMe2COOMe and H2CCMeCMe2COOMe, formed from two radicals 3 in a radical pair. In CDCl3 solution, however, emissions are found for the unsaturated ester, CHCl3 and CHDCl2, and an A/E signal for the saturated ester. The chlorinated products are formed from the •CCl3 and •CDCl2 radicals and a hydrogen donor.

The benzylic radical 8 gives rise to an A/E multiplet effect (in benzene) for the combination product dimethyl 3,4‐diphenyladipate (9) and the disproportionation product methyl cinnamate (11).
Folded conformations. Part VIII. Does intramolecular donor/acceptor interaction affect the basicity of p‐(N,N‐dimethylamino)benzyl p‐nitrophenyl sulfone?
Authors: Bleeker I. P. , Engberts Jan B. F. N.
Published: September 2010

Comparison of the equilibrium basicity of the title sulfone (1) with that of some reference compounds indicates that the ground state of 1 is not affected by intramolecular charge transfer from the donor to the acceptor ring.
Chemistry of tetraalkoxyethenes VIII Hydrolysis and subsequent decarboxylation of ethyl 2,2,3,3‐tetraalkoxy‐1‐cyanocyclobutanecarboxylates
Authors: Ooms P. H. J. , Bos R. P. , Scheeren J. W. , Nivard R. J. F.
Published: September 2010

Treatment of ethyl 2,2,3,3‐tetraalkoxy‐1‐cyanocyclobutanecarboxylates (7), obtained by heating tetraalkoxyethenes with ethyl 2‐cyano‐2‐alkenoates at 100°, with a dilute methanolic solution of sodium hydroxide at 50° leads to hydrolysis of the ester function. On prolonged heating at higher temperatures the resulting products 8 decarboxylate, yielding 2,2,3>3‐tetraalkoxycyclobutanecarbonitriles 9. Under these conditions the nitrile group is also partly hydrolysed to a carboxylic acid function. Depending on the pH, acidification of 8 yields either rearranged, six‐membered ring compounds, viz. 4,4,5,5‐tetraalkoxy‐2‐cyano‐δ‐valerolactones 12, or acyclic acetals of α‐keto esters 13.
A reinvestigation of the mechanism of the amination of 5‐bromo‐4‐t‐butylpyrimidine. On the occurrence of an SN(ANRORC) mechanism
Authors: Rasmussen C. A. H. , van der Plas H. C.
Published: September 2010

Evidence is presented that the cine‐substitution of 5‐bromo‐4‐t‐butyl[1(3)‐15N]pyrimidine into 6‐amino‐4‐t‐butyl[x‐15N]pyrimidine by potassium amide in liquid ammonia takes place to a considerable extent via an 5N(ANRORC) mechanism involving an addition of amide ion to C(2) of the pyrimidine ring. The currently accepted view that this conversion proceeds via a “hetaryne mechanism” has to be revised.
The photochemistry of previtamin D and tachysterol
Authors: Jacobs H. J. C. , Boomsma F. , Havinga E. , van der Gen A.
Published: September 2010

Pathways of formation are discussed for the thirteen toxisterols, the isolation and structure determination of which have been dealt with in the preceding article. It is suggested that toxisterols A (C‐8 spiro compounds) and C (bicyclo[3.1.0]hexenes) originate from previtamin D through relaxation of the excited“tZc”form of its hexatriene system. The symmetry‐allowed conrotatory closure to a 5–6–10 cyclopropane ring constitutes a plausible first step for both reactions. The description of the formation of the bicyclohexene moiety of toxisterol C1 as a two‐step process is consistent with its stereochemistry; the configuration corresponds to an overall [π4a+π2a] route and not to the [π4s+π2a] pathway expected for a concerted photochemical process. For the formation of toxisterols A a series of steps following the initial cyclopropane ring closure ‐ comprising a hydrogen shift from C‐4 to C‐9 and bond formation between C‐4 and C‐8 ‐ to provide the C‐8 spirostructure is proposed. Toxisterol D1 can be formed from previtamin D (or tachysterol) by a photoinduced antarafacial [1,5] hydrogen shift. The cyclobuteno compound toxisterol E1 originates from excited tachysterol through a disrotatorye ring closure of the 6‐7‐8‐9 butadiene moiety.

A rationalization is offered for the novel photochemical 1,6‐addition of alcohol to the conjugated triene system of previtamin D/tachysterol yielding the toxisterols B, as well as for the photoreduction to form toxisterol R1. The article concludes with comments on the general picture of photoconversions as it emerges from previous and present investigations.
Redox properties of copper, nickel and palladium complexes with amidato ligands
Authors: Bour J. J. , de Brugh‐Arts J. H. M. Aan , Hendriks H. M. J. , Steggerda J. J.
Published: September 2010

Cu(II), Ni(II) and Pd(II) complexes of the terdentate ligands 1‐(2‐pyridylmethylene)biuret and 1‐(2‐hydroxylphenyl)biuret (abrv. as pybiH2 and phHbiH2, respectively) have been prepared and their spectral, magnetic and voltammetric properties studied. In a square‐planar coordination the metals are bonded to the pyridine N (in the pybi compounds) or to the phenolato O (in the phHbiH2 compounds) and to one or two deprotonated amide N's in [Cu(pybiH)(H2O)]+, Pd(pybiH)Cl and [Cu(phbiH)]2 respectively in Cu(pybi)(H2O) and [Ni(pybi)(OH)]− Comparison with other biuretato complexes of Cu reveals that increasing the number of coordinated amide N's goes parallel with increasing energy of the spectral dd transition and with a decrease of half wave potentials for the oxidation to Cu(III) as well as for the reduction to Cu(I) compounds. The redox orbitals seems to be located mainly on the metal centre in accord with previous MO calculations.
The electrocatalytic reduction of nitrogen compounds Part I: The electrochemical reduction of nitrite at a rotating platinum ring‐disc electrode
Authors: van der Plas J. F. , Barendrecht E.
Published: September 2010

The mechanism of the electrochemical reduction of nitrite has been studied at a rotating ring‐disc electrode. It is found that the reduction of nitrite to nitric oxide is a reversible process. The reduction of nitric oxide to hydroxylamine involves the intermediate HNO, from which dinitrogen oxide can be formed in a side reaction to the reduction process.
Beckmann rearrangement of aldoximes catalyzed by transition metal salts: Mechanistic aspects
Authors: Leusink A. J. , Meerbeek T. G. , Noltes J. G.
Published: September 2010

The Beckmann rearrangement of aldoximes catalyzed by transition metal salts proceeds by a dehydration‐hydration reaction. A mechanism is proposed in which nitrile is bound to an oxime‐metal complex; subsequently, water (as OH− and H +) is transferred from oxime to nitrile in the ligand sphere of the metal, yielding nitrile and amide, respectively.
Derivatives of meta‐di‐tert‐butylbenzene. Part IV Dissociation constants of 2‐halogeno‐3,5‐di‐tert‐butylbenzoic acids
Authors: de Koning Adrianus Jan
Published: September 2010

The preparation of 2‐chloro‐, 2‐bromo‐ and 2‐iodo‐3,5‐di‐tert‐butylbenzoic acid is described and a possible explanation for their unexpectedly high dissociation constants is given.
The photo‐oxidation of hexamethylbenzene by singlet oxygen
Authors: van den Heuvel C.J.M. , Steinberg H. , de Boer Th.J.
Published: September 2010

In the dye‐sensitized photo‐oxidation of hexamethylbenzene two molecules of singlet oxygen are rapidly taken up: one of the oxygenation steps involved is an ene‐type reaction, and the other a [4 + 2]‐cycloaddition. The resulting endoperoxy hydroperoxide 2 can be reduced selectively to the corresponding endoperoxy alcohol 3 and by further reduction to the triol 4. X‐ray analysis shows the hydroperoxy group and the OO bridge in 2 to be on different sides of the cyclohexyl ring.
Réarrangement de dérivés des thiolannones‐2
Authors: Brisset G. , Morin L. , Paquer D. , Rioult P.
Published: September 2010

Various nucleophiles (sodium methoxide, hydride ion, thiolates and carbanions derived from organomagnesium compounds and ketones) react with 3‐[bis(methylthio)methylene]‐2‐thiolanones giving a rearrangement. The mechanism of the proposed rearrangement has been investigated. The reaction of enolate ions with thiolanones produces new β‐diketones.
Total synthesis of methyl t‐5,c‐8,c‐11,c‐14‐ and c‐5,c‐8,c‐11,t‐14‐eicosatetraenoate and of t‐2,c‐5,c‐8,c‐11,c‐14‐eicosapentaenoic acid
Authors: Egmond G.J.N. , Pabon H.J.J. , van Dorp D.A.
Published: September 2010

On the basis of trans‐2‐hexene‐1,6‐diol and trans‐2‐octenol, both obtained by trans reduction of their acetylenic precursors with sodium in liquid ammonia, trans‐5‐eicosene‐8,1 1,14‐triynoic acid and trans‐ 14‐eicosene‐5,8,11‐triynoic acid were built up by classical methods. Partial hydrogenation and esterification afforded the desired eicosatetraenoates. In addition, reduction of previously described trans‐2‐eicosene‐5,8,11,14‐tetraynoic acid gave t‐2,c‐5,c‐8,c‐11,c‐14‐eicosapentaenoic acid.
Vapour phase chemistry of arenes. Part VII: Direct, thermal cyanation of benzene derivatives and pyridine by hydrogen cyanide
Authors: van Nierop Kees , Louw Robert
Published: September 2010

Benzene, chlorobenzene or benzonitrile, in the presence of a little C2Cl6 or formaldehyde, reacts with HCN at ∼ 480° (30 s) to give the (mono)cyano derivatives. Features, especially isomer distributions for this cyanation closely resemble those for gas‐phase chlorination. By analogy, therefore, a free radical mechanism is advanced involving endothermal hydrogen abstraction by Cl• and/or H• to give aryl radicals, which in turn attack HCN at carbon, displacing hydrogen. Pyridine leads to cyanopyridines (89 % 2‐, 6 % 3‐, 5 % 4‐isomer), the 2‐position being ∼ 3 times as reactive as benzene hydrogens. This supports our view that differences in CH bond strength play a major part, as it is known that 2‐pyridyl is stabilized relative to its 3‐ and 4‐analogues. ICN was found not to be a suitable alternative for HCN.
Bis‐heterocycles. Part III.: Synthesis of tetramethylene‐3,3′‐di‐1,2,4‐triazoles and tetramethylene‐2,2′‐di‐1,3,4‐thiadiazoles
Authors: Ram Vishnu Ji , Pandey H.N.
Published: September 2010

Tetramethylene‐4,4′‐bis(1‐arylthiosemicarbazides) were converted into tetramethylene‐3,3′‐bis(4‐aryl‐5‐mercapto‐1,2,4‐triazoles) and tetramethylene‐2,2′‐bis[5‐(arylamino)‐1,3,4‐thiadiazoles] under different reaction conditions. The bis(5‐mercapto‐1,2,4‐triazoles) were converted into their thiolates on treatment with alkyl halides. Some compounds were found to be active pesticides.
Synthesis and chiroptical properties of (‐)‐(S)‐2‐chloro‐3‐(5‐imidazolyl)propanol (Imidazole chemistry, Part II)
Authors: Beyerman H.C. , van Weelderen A. W. Buijen , Maat L. , Noordam A.
Published: September 2010

(‐)‐(S)‐2‐Chloro‐3‐(5‐imidazolyl)propanol (4) was synthesized by reduction of both the acid chloride and the methyl ester of (‐)‐(S)‐2‐chloro‐3‐(5‐imidazolyl)propionic acid. The optical rotatory dispersion and circular dichroism spectra are discussed.
A quantumchemical study of the C6H+5 potential energy surface. Evidence for a nonclassical pyramidal carbenic species
Authors: Castenmiller W.A.M. , Buck H.M.
Published: September 2010

MINDO/3 and STO‐3G MO calculations including geometry optimization have been performed for nonlinear C6H+5 structures. The phenyl cation 5 is the lowest energy compound on the surface, followed by the nonclassical pyramidal carbenic structure 4. Other local minima include the bicyclic carbene 6 and the benzvalenyl cation 7. Fairly good agreement between the results from both methods was obtained. The electronic structure of 4 is explained using orbital interaction diagrams which show the stabilization of the cyclopentadienyl cation by the apical carbon atom and the relation between 4 and pyramidal transition‐metal complexes. The electronic structure of 6 is related to that of the bicyclo[3.1.0]hexenyl cation 12. Activation energies for rearrangement reactions on the energy surface show that 4 can probably be studied starting from benzvalene‐type precursors.
Boron trifluoride catalysed rearrangement and decarbonylation of quinoid γ‐oxo‐α,β‐unsaturated thiolesters. α‐Alkylthio‐γ‐lactones
Authors: Mosterd A. , Bos H.J.T.
Published: September 2010

Under the influence of boron trifluoride quinoid γ‐oxo‐α,β‐unsaturated thiolesters (5) and (10) rearrange into α‐alkylthio‐γ‐lactones (6) and (9), respectively, in yields of 50–90%. In the case of S‐alkyl 2‐(10‐oxo‐9‐phenanthrenylidene)alkanethioates (13) decarbonylation occurs with formation of α,β‐unsaturated ketones (14). Mechanisms are proposed. The γ‐oxo‐α,β‐unsaturated thiolesters were prepared in situ from a 1‐alkynyl sulfide and 3,5‐di‐tert‐butyl‐o‐benzoquinone or 9,10‐phenanthroquinone, under the influence of boron trifluoride.
Thiophene analogues of estrone; synthesis and structural assignment
Authors: Corvers A. , Scheers P.C.H. , de Haan J.W. , Buck H.M.
Published: September 2010

The synthesis of tetracycles of type 1 is described. Both la and lb are converted into the estrogen‐like compounds 12a and 12b via the corresponding α‐epoxides. The β‐epoxides yield mixtures of dienes. The stereochemical influence of the base on the alkene precursors for tetracyclic compounds, formed under Wittig‐Schlosser conditions, has been established. Finally, evidence is offered for the trans,anti,trans geometry in the tetracyclic molecules under discussion.
Preparation, structure and properties of complexes with the bis(di‐n‐butyldithiocarbamato)arsenic(III) or antimony(III) cation
Authors: van de Leemput P. J. H. A. M. , Cras J.A. , Willemse J.
Published: September 2010

The preparation, structure and some physical properties of cationic dithiocarbamatoarsenic(III) and ‐antimony(III) compounds [M(Bu2dtc)2] + X− [X = I−3 for M = As and Sb; X = Cd2I2−6 for M ‐ Sb and Bu2dtc− = Bu2NC(S)S−] are reported. [Sb(Bu2dtc)2]2Cd2I6, crystallizing in the monoclinic space group P21/n with a = 16.236(6), b = 12.573(5), c = 16.126(5) Å, β = 94.13(2)°, V = 3283 Å3 and Z = 2, contains Sb in pseudo‐trigonal‐bipyramidal coordination, with a stereoactive lone pair in an equatorial position. The Bu2dtc groups are asymmetrically bonded, with their largest Sb‐S bonds in equatorial direction.
Synthesis of substance P via its sulfoxide by the repetitive excess mixed anhydride (REMA) method
Authors: Izeboud E. , Beyerman H. C.
Published: September 2010

The N‐protected heptapeptide sulfoxide corresponding to positions 5 to 11 inclusive of substance P, Boc‐Gln‐Gln‐Phe‐Phe‐Gly‐Leu‐Met(O)‐NH2 (VII), was synthesized by the repetitive excess mixed anhydride (REMA) method (Scheme). Consecutive mixed anhydride coupling to N‐deprotected VII of the dipeptides Boc‐Lys(Z)‐Pro‐OH (VIII) and Z‐Arg(NO2)‐Pro‐OH (X) yielded protected substance P sulfoxide, XI. From XI both Z groups and the NO2 group were removed with liquid hydrogen fluoride, yielding substance P sulfoxide.

Substance P sulfoxide was conveniently reduced to substance P with the aid of iodide ions in strongly acid olution. Preliminary results are given on the scope of this method, i.e. peptides containing ‐ besides methionine ‐ tyrosine, where the method worked well, or tryptophan, where the method failed.

REMA‐synthesized substance P, after gel filtration, was found to be chemically pure and to possess the same biological activity as a substance P standard (Beckman), according to two tests (sialagogic assay and guinea pig ileum contraction).
Synthese von Bicyclo[3.2.n]alka‐2,6‐dienen und Bicyclo[3.2 + n.0]alka‐2,n + 4‐dienen aus 1,3‐cycloalkadienen
Authors: Japenga J. , Klumpp G. W. , Kool M.
Published: September 2010

Thermolysis (350°C, 2 sec) of mixtures of the endo‐ and exo‐epimers of (n + 5)‐vinyl‐bicyclo[n + 2.1.0]alk‐2‐enes [n = 2, 3, 4; prepared by a sequence of reactions starting with the addition of (methoxycarbonyl)carbene to an appropriate 1,3‐cycloalkadiene] yields bicyclo[3.2.n]‐alka‐2,6‐dienes. Bicyclo[5.3.0]deca‐2,7‐diene is obtained by thermolysis (550°C, 2 sec) of bicyclo‐[3.3.2]deca‐2,9‐diene.
Oxydation des alcools. II ‐ Mesure des effets isotopiques secondaires du deutérium pour déterminer le mécanisme de l'étape lente de la réaction d'oxydation par le chrome (VI)
Authors: Durand R. , Geneste P. , Lamaty G. , Moreau C. , Pomarès O. , Roque J. P.
Published: September 2010

The nature of hydrogen transfer occurring during the slow step of the oxidation reaction of the alcohol using chromic acid has been studied by measuring the secondary deuterium isotope effects. The results obtained with cyclohexanol (kH/kD = 1.25); cis‐4‐tert‐butylcyclohexanol (kH/kD = 1.44); trans‐s‐4‐tert‐butylcyclohexanol (kH/kD = 1,10); exo‐2‐norbornanol: exo‐3‐d1 (kH/kD = 0.99), endo‐3‐d1 (kH/kD = 1.09), 3‐3‐d2 (kH/kD = 1.07); endo‐2‐norbornanol: exo‐3‐d1 (kH/kD = 1.05), endo‐3‐di (kH/kD = 1.00) and 3‐3‐d2 (kH/kD = 1.07) are more in agreement with a proton transfer than with a hydride transfer if there is no important structural modification of the chromic esters.
Ring transformations of heterocycles by oxidizing agents. A 14C study of the conversion of cinnolines into indazoles
Authors: van der Plas H. C. , Buurman D. J. , Vos C. M.
Published: September 2010

5‐Nitro‐ and S‐nitro[4‐14C]cinnoline have been prepared. Oxidation of those compounds by hydrogen peroxide in acetic acid gave 4‐nitro[3‐14C]‐ and 7‐nitro[3‐14C]indazole, respectively. The indazoles have nearly the same specific radioactivity as the cinnolines, leading to the conclusion that only the C(3) atom of the cinnoline ring is expelled. A mechanism for the ring transformation is proposed.
2‐(Arylimino)imidazolidines; synthesis and hypotensive activity
Authors: Timmermans P. B. M. W. M. , van Zwieten P. A. , Speckamp W. N.
Published: September 2010

The synthesis of various 2‐(arylimino)imidazolidines is described. Most compounds were prepared by reaction of N‐aryl‐S‐methylisothiuronium iodides or N‐aryldichloroimines with ethylene‐diamine. The derivatives differ in substitution in the aromatic moiety. The hypotensive activity of the imidazolidines has been measured following intravenous administration to anaesthetized, normotensive rats. Big differences in hypotensive activity exist within the present series of structurally related compounds.
A new synthesis of allenic hydrocarbons from tertiary 2‐propynyl sulfinates and organocopper(I) compounds. Evidence for a syn‐l,3‐substitution pattern in the steroid series
Authors: Vermeer P. , Westmijze H. , Kleijn H. , van Dijck L. A.
Published: September 2010

In tetrahydrofuran tertiary 2‐propynyl sulfinates R1‐C≡C‐C(R2,R3)‐OS(O)Me (1) are smoothly converted in a 1,3‐substitution reaction into allenic hydrocarbons RR1CCCR2R3 (4) by organoheterocuprates of the type (RCuBr)MgX. Generally, much attack on the sulfur atom in 1 is observed when this compound is treated with (RCuBr)MgX in diethyl ether, or with R2CuMgX in diethyl ether or in tetrahydrofuran. The stereochemical course of the allene formation has been studied in the case of the sulfinic ester 5, derived from the steroid “Mestranol”. It is found that the syn‐1,3‐substitution product 6 is exclusively formed from 5 and the heterocuprates (MeCuBr)MgCl or (MeCuBr)MgCl·LiBr. Most likely, copper(III) species are formed in the first step of the 1,3‐substitution reactions described.
The electrocatalytic reduction of nitrogen compounds. Part II: The influence of the electrode material on the electrochemical reduction of nitrite
Authors: van der Plas J. F. , Barendrecht E.
Published: September 2010

The electrochemical reduction of nitrite was studied at several electrode materials in 7.5 M sulfuric acid solutions. The thin oxide films on the noble metals, Pt, Ir and Rh, did not interfere with the reduction process. A thick oxide layer, as on Nb and Ta, however, did shift positively the reducing potential by several hundreds of mV.

In these solutions, the protecting layer on a lead electrode (lead sulfate) behaved in the same manner. From the decrease in the current in repeated cyclic experiments, it could be concluded that poisoning of the active surface sites of the electrodes by oxygen did change the reduction mechanism of nitrite.
Asymmetric induction in electropinacolization
Authors: van Tilborg W. J. M. , Smit C. J.
Published: September 2010

Asymmetric induction could be achieved in the electrochemical reduction of ketones to pinacols in acetonitrile as solvent by using asymmetric conducting salts.
On the conformation and dimerization of a 2‐mercapto‐5‐methylenepiperazine‐3,6‐dione
Authors: Noordik Jan H. , Herscheid Koos D. M. , Tijhuis Marianne W. , Ottenheijm Harry C. J.
Published: September 2010

An X‐ray crystal structure analysis of 9,9a‐dihydro‐l,9,9‐trimethyl‐2‐methylene‐3,10‐diketo‐9a‐mercapto‐piperazino[1,2‐a]indole (1) shows a boat conformation for the piperazinedione ring in this compound. This observation supports the previously suggested Zn++ chelate 3 as an intermediate in the conversion of 1 into 2. Crystals of 1 are monoclinic, a = 12.751 (7)å, b = 7.439 (2) Å, c = 15.324 (15) Å,β = 98.73(6)°; space group: P21/n,Z = 4. In solution at room temperature 1 dimerizes to 4 with loss of one molecule of H2S.
A NMR study on the ring contraction of N‐methylpyrimidinium salts into pyrazoles
Authors: Brouwer M. S. , van der Plas H. C. , van Veldhuizen A.
Published: September 2010

1H‐NMR evidence is presented for the covalent hydrazination of 1‐methyl‐, 1,2‐dimethyl‐, 1,4,6‐trimethyl‐ and l‐methyl‐4‐phenyl‐pyrimidinium iodide (1a‐d) at C(6). With fully deuterated hydrazine hydrate the salts 1a‐d undergo ring contraction into pyrazole and pyrazole derivatives (8a‐d) containing deuterium at position 4. Evidence is presented for the intermediacy of a tautomeric mixture of open‐chain compounds, in which H/D exchange occurs before cyclisation takes place.
Long‐range carbon‐proton spin‐spin coupling constants. A 13C NMR study of monohalogen substituted ethanes and propanes
Authors: Spoormaker Tom , de Bie Marius J. A.
Published: September 2010

The analysis of single resonance 13C FT NMR spectra has provided all long range 13C‐1H coupling constants in the monohalogeno‐ethanes and ‐propanes. In addition, all directly bonded 13C‐1H coupling constants, 13C‐chemical shifts as well as 1H‐NMR data are reported (together with literature values). Substituent effects on the geminal and vicinal 13C‐1H coupling constants are discussed in terms of electronegativity, conformation and bond polarization.
The chemistry of small‐ring compounds. Part 40. Protonated and methylated methyleneaziridines
Authors: Jongejan E. , Steinberg H. , de Boer Th. J.
Published: September 2010

The N‐substituted methyleneaziridines 1a‐c are protonated on nitrogen without ring rupture by HFSO3/SbF5 in SO2 at − 78°C. NMR spectra remain unchanged up to + 50°C. Methylation of la does not take place with ordinary methylating agents but can be achieved with (CH3)2Cl⊕SbF5Cl⊖.
α‐Amino acid dehydrogenase models. Reduction of an imine and of iminium salts of α‐keto esters by 1,4‐dihydropyridines (Preliminary communication)
Authors: Pandit Upendra K. , de Nie‐Sarink Margreet J. , van der Burg Alida M. , Steevens Jan B. , van Dokkum Ronald F. M.
Published: September 2010

3,5‐Di(ethoxycarbonyl)‐2,6‐dimethyl‐1,4‐dihydropyridine (Hantzsch ester) reduces imines (in the presence of Mg+ + ions) and iminium salts, derived from α‐keto esters.
The exchange of alkanediammonium ions in the zeolites X and Y
Authors: Vansant E. F. , Vanhoof L.
Published: September 2010

A study has been made of the exchange properties of +H3N‐CH2‐NH+3, +H3N‐(CH2‐NH+3, +H3N‐(CH2)3‐NH+3, +H3N‐CH2‐CH(NH+3)‐CH3, +H3N‐(CH2)4‐NH+3, +H3N‐(CH2)5‐NH+3 and +H3N‐(CH2)6‐NH+3 in the zeolites X and Y.

For steric reasons, none of the organic cations could effect a complete replacement of the Na+ ions initially present in the zeolite. A linear decrease and increase between the maximum extent of exchange and the molecular weight of the alkanediammonium ions were found for the zeolites X and Y, respectively. For any given alkanediammonium ion the maximum exchange capacity decreases with an increase in the affinity of the cations initially present in the zeolite, the order being Li+ > Na+ > K+. It is suggested that the localisation of the initial inorganic cations, influenced by the affinity of the ingoing organic cations and the difficulties of packing of the organic ions, controls the maximum extent of exchange.
Structure elucidation of the photo‐oxidation product of 1‐(9‐phenanthryl)‐4‐phenylbut‐1‐en‐3‐yne
Authors: van Arendonk R. J. F. M. , Laarhoven W. H. , Prick P. A. J.
Published: September 2010

The photo‐oxidation product of 1‐(9‐phenanthryl)‐4‐phenylbut‐1‐en‐3‐yne has been elucidated by chemical and spectroscopic methods (IR, UV, 1H‐NMR, 13C‐NMR) and independently by X‐ray analysis. The structure 6‐phenyl‐8,9‐10,11‐dibenzotricyclo[5.4.0.01,6]‐4‐oxaundeca‐2,8,10‐trien‐5‐one has a cyclopropapyrone unit which decomposes on thermolysis or by catalytic hydrogenation.
Recherches en série triazépine‐1,2,4 XIII. Hydrazinolyses de thioxo‐3 oxo(thioxo)‐5 triazépines‐1,2,4
Authors: Hasnaoui A. , Lavergne J.‐P. , Viallefont Ph.
Published: September 2010

The ring interconversion of 2,7‐dimethyl‐3‐thioxo‐5‐oxo(thioxo)‐1,2,4‐triazepines into pyrazolones, 3‐hydrazinopyrazoles or tetrazocyne by hydrazinolysis are described.

The hydrazine and methylhydrazine reactions afforded 2‐methyl thiosemicarbazide and 3(5)‐pyrazolones by breaking of the two N(1)‐C(7) and N(4)‐C(5) bonds in the triazepinone ring. The reaction with phenylhydrazine is different. In this case three reaction centres must be taken into account: 3, 5 and 7 positions.

Hydrazinolysis of 5‐thioxo‐1,2,4‐triazepine is more complicated and depends on the experimental conditions. The mechanism suggested is addition of two molecules of hydrazines in the 5 position followed by a transannular reaction to the 7 position for hydrazine and to the 3 and 7 position for phenylhydrazine.
Transsubstitution and equilibrium of phenols. Part III. Transbromination of phenols in the presence of aluminium phenoxide and other acidic catalysts
Authors: Jonkheer P. C. Th. M. , Moen J. , Wolters J. , Kooyman E. C.
Published: September 2010

Intra‐ and inter‐molecular bromine migrations in bromophenols occur in the presence of catalytic amounts of aluminium phenoxides or proton acids (such as sulfuric and trifluoromethanesulfonic acid) at temperatures between 80 and 180°C. Under these conditions only ortho and para positions are involved; no meta‐bromophenols are formed.

The equilibrium constants for the ortho‐ortho transsubstitution (Kx = [2‐bromo‐4‐X‐phenol]2/[2,6‐dibromo‐4‐X‐phenol] [4‐X‐phenol = 15 ± 3) are independent of substituents in the para position. The equilibrium constants for the ortho‐para isomerization are calculated (R2/4 = [2‐bromophenol]/[4‐bromophenol] = 1.9±0.3; R2,6/2,4 = [2,6‐dibromophenol]/[2,4‐dibromophenol] = 0.34± 0.04). Kinetic data ‐ some of them suggesting second‐order kinetics ‐ are given. A mechanism is proposed.
The solvent effect on the enthalpy of hydrolysis of cyclic adenosine 3′,5′‐monophosphate. A quantumchemical study
Authors: Scheffers‐Sap M. M. E. , Buck H. M.
Published: September 2010

The solvent effect on the enthalpy of hydrolysis has been studied by the Extended‐Hückel method for the hydrolysis reactions of cyclic adenosine 3′,5′‐monophosphate (cyclic 3′,5′‐AMP) and related cyclic phosphate diesters. The results show that the difference in enthalpy of hydrolysis between cyclic 3′,5′‐AMP and related phosphate diesters is explained by the difference in net solvation enthalpy. The larger exothermic net solvation enthalpy of cyclic 3′,5′‐AMP can be ascribed to an extra stabilization of the hydrolysis product with respect to the reactants, which does not occur for the other cyclic phosphate diesters. The extra stabilization is due to hydrogen bonding with water between O(1′) and O(5′) in both adenosine 5′ ‐ and 3′‐monophosphate.
Ring transformations in reactions of heterocyclic compounds with nucleophiles (XXI): Conversion of 5‐nitropyrimidine into pyridines and benzene derivatives by ketones
Authors: Barczyński P. , van der Plas H. C.
Published: September 2010

Reaction of 5‐nitropyrimidine with ketonic reagents such as acetone, diethyl ketone, dibenzyl ketone and acetylacetone in the presence of triethylamine or potassium ethoxide gave either the 5‐nitropyridine derivatives 1, the 4‐nitrophenol (2) or the 4‐pyridone (3). These reactions show the first examples of the conversion of a pyrimidine ring into a benzene ring. The reaction pattern strongly depends on the nature of the ketone and the base used. The mechanism of these ring‐transformation reactions involves the initial addition of the anion of the ketone to either C(6) (leading to 1 or 2) or C(2) (giving 3).
Selective photochemical isomerizations of E,E‐germacra‐1(10),4,7(11)‐trien‐8‐one
Authors: Reijnders Peter J. M. , Buck Henk M.
Published: September 2010

Direct irradiation of title compound 1 causes isomerization of the 1(10)‐double bond to give the 1(10)Z,4E‐isomer 2, due to selective energy transfer in the β,γ‐enone fragment formed by the carbonyl group and the 1(10)‐double bond. Acetophenone‐sensitized irradiation in n‐hexane leads to the completely isomerized 1(10)Z,4Z‐germacrone 3. 1(10)E,4Z‐Germacrone could not be prepared photochemically.
Préparation de cyclobutanones substituées par l'intermédiaire de dérivés sulfurés
Authors: Paquer D. , Reffet D. , Vazeux M.
Published: September 2010

Substituted cyclobutanones have been obtained from the corresponding 1,3‐diones by converting one oxo group in the latter compounds into sulfur containing group(s) and subsequently removing the S group(s) with Raney‐Nickel. The mass spectral fragmentation patterns of these compounds are discussed.
Aspects of the amination of 4‐t‐butyl‐5‐halogenopyrimidines by potassium amide in liquid ammonia
Authors: Rasmussen C. A. H. , van Der Plas H. C.
Published: September 2010

The amination of 5‐bromo‐2,4‐di‐t‐butylpyrimidine (11b), 5‐chloro‐2,4‐di‐t‐butylpyrimidine (11c) and 4‐t‐butyl‐5‐chloropyrimidine (11a) on treatment with potassium amide in liquid ammonia has been studied. 11b yields 6‐amino‐2,4‐di‐t‐butylpyrimidine (7b) as major product. In contrast, 11c and 11a give 6‐amino‐5‐chloro‐2,4‐di‐t‐butylpyrimidine (12c) and 6‐amino‐4‐t‐butyl‐5‐chloropyrimidine (12a), respectively as main products, together with minor quantities of 7b and 6‐amino‐4‐t‐butylpyrimidine (7a). Choice of halogen and accessibility of C(2) of the pyrimidine nucleus influence the mechanism of the amination. An SN(ANRORC) mechanism is not operative in any of the conversions described.
Complex formation of adenine and 9‐methyladenine with transition metal salts in ethanol
Authors: Guichelaar M. A. , Reedijk J.
Published: September 2010

The coordination chemistry of adenine and 9‐methyladenine towards transition‐metal ions has been studied. Solid compounds of the formula M(AH)2X2 were isolated and characterised for M = Ni, Cu, Zn and Cd and X = Cl, Br, NO3 and ClO4; AH standing for adenine. With 9‐methyladenine (MA) solid compounds formulated as M(MA)X2(M = Co, Ni, Cu, Zn and Cd; X = Cl and Br) and formula M(MA)2(NO3)2‐nH2O (M = Co and Ni with n = 2 and M = Cu, with n = 1) have been synthesized.

The compounds were characterised by chemical analysis, infrared spectra, far‐infrared spectra, ligand‐field spectra, X‐ray powder diagrams, ESR powder spectra and magnetic susceptibility measurements. Despite several attempts, no compounds containing more than two of these ligands per metal ion could be òbtained. Extensive ligand‐ligand and ligand‐anion hydrogen bonding may account for this result.

With a few exceptions adenine appears to coordinate via N(9) in monomeric compounds and via N(3) and N(9) in dinuclear compounds. The respective coordination sites in 9‐methyladenine complexes are N(7) in the case of monodentate coordination, and N(1) and N(7) in the case of bidentate bridging coordination.
Catalytic inhibition of hydrocarbon autoxidation by secondary amines and nitroxides
Authors: Bolsman T. A. B. M. , Blok A. P. , Frijns J. H. G.
Published: September 2010

A study has been made of the catalytic inhibition of the autoxidation of hydrocarbons at 130°C by secondary amines and derivatives thereof (hydroxylamines and nitroxides). Owing to a better resistance towards side‐reactions that cause decomposition of the inhibitor, certain dialkylamines are much more efficient than diarylamines. Some of the dialkylamines examined are capable of scavenging several hundreds of propagating radicals per molecule of inhibitor in autoxidizing alkanes and a few thousand radicals in autoxidizing n‐hexylbenzene.
Factors influencing the occurrence of an SN(ANRORC) mechanism in the amino‐dehalogenation of 4‐substituted 6‐halogenopyrimidines by potassium amide in liquid ammonia
Authors: Rasmussen C. A. H. , van der Plas H. C.
Published: September 2010

Evidence is presented by means of 15N‐labelling that the occurrence of an SN(ANRORC) mechanism in the amino‐dehalogenation of 4‐substituted 6‐halogenopyrimidines by potassium amide in liquid ammonia is dependent on at least two factors. The C(2) position must be readily accessible to the attacking amide ion and the substituent at C(4) must not contain an acidic hydrogen atom adjacent to the pyrimidine nucleus. It is shown that the amount to which an SN(ANRORC) process occurs can be dependent on the reaction temperature.
Nitrogen fixation by reduced transition metal complexes. II. The influence of lithium and naphthalene as reducing species on vanadium trichloride
Authors: Beelen T. P. M. , Rummens C. P. J.
Published: September 2010

VCl3 is able to bind dinitrogen at room temperature and a N2 pressure of 1 atmosphere after reduction with Li+Np− (Np = naphthalene) or with Li + Li+Np2−. In the latter case also a direct reaction of N2 with Li + Li2+Np2− occurs, so that there are two independent nitrogen fixation reactions effective in the system VCl3 + Li + Li2+Np2−. The role of Np2− ions in this system has been investigated and a proposal for the mechanism of the reaction of Li + Li2+Np2− with N2 is made.
3‐Methyl‐2‐chloro‐2‐hydroxy‐2‐phosphanaphthalene. A stable p‐hydroxy‐λ5‐phosphorin
Authors: Klebach Th. , Jongsma C. , Bickelhaupt F.
Published: September 2010

3‐Methyl‐2‐chloro‐2‐hydroxy‐2‐phosphanaphthalene (3) is obtained from the dihydroprecursors 6 and 14 by treatment with COCl2 followed by triethylamine. Contrary to other P‐hydroxy‐λ5‐phosphorins, 3 is thermally surprisingly stable. Protons catalyze its rearrangement to the thermodynamically more stable isomer 3‐methyl‐2‐chloro‐1,2‐dihydro‐2‐phosphanaphthalene 2‐oxide (5). Some aspects of the formation of 3 are discussed.
An NMR study of the thermal decomposition of dimethoxycarbenium bromides
Authors: Dusseau Ch. H. V. , Steinberg H. , de Boer Th. J.
Published: September 2010

Bromination of the methyl ortho esters 1a‐i in liq. SO2 at −80°C gives rapidly the dimethoxycarbenium bromides 2a‐i together with methyl hypobromite. The aliphatic bromides 2a‐g display two distinct methoxyl NMR absorptions, suggesting a “cis‐trans” configuration. The aromatic bromides 2h‐i show only one methoxyl absorption, which can be explained by assuming the symmetrical “cis‐trans” conformation of the aryldimethoxycarbenium ion.

The bromides 1a‐i are stable up to −50°C and are converted into the corresponding methyl ester 5 and methyl bromide 6 at higher temperatures. During the thermal decomposition of 2a‐i line broadening of the methoxyl absorptions are observed, either due to rotation of the methoxyl groups around the C‐O bonds in the dimethoxycarbenium ion D and/or by a rapid equilibrium between ionic and covalent forms D and E.
Chemistry of small‐ring compounds. Part 42. The rearrangement of methyleneaziridinium ions to cyclopropaniminium ions
Authors: Jongejan E. , Steinberg H. , de Boer Th. J.
Published: September 2010

A kinetic study in FSO3H/SbF5 reveals that the 1‐methyl‐2‐methyleneaziridinium ion 4 rearranges in a first order reaction to the ring‐opened enammonium ion 6. At temperatures below 80° this process takes place via isomerisation of the methyleneaziridinium ion to an intermediary cyclopropaniminium ion 5. At higher temperatures the direct conversion 4 → 6 ‐ which is negligible in the lower temperature region ‐ must also be taken into account (cf. Scheme 4).

1,1‐Dimethyl‐2‐methyleneaziridinium fluorosulfate undergoes a similar heterocyclic ‐ homocyclic ring rearrangement in FSO3H, but higher temperatures (115°) are required.

The rearranged product, N,N‐dimethylcyclopropaniminium fluorosulfate is much more stable than the mono‐N‐methyl derivative i.e. it can be heated up to 150° without decomposition. By analogy the methyleneaziridinium → cyclopropaniminium isomerisation is thought to take place via a ring‐opened biradical cationic species rather than via a diamagnetic 2‐(mono‐ or dialkylamino)allyl cation.
Identification of chiral 1,2‐diacylglycerols in fresh milk fat
Authors: Lok C. M.
Published: September 2010

Trityl chloride, which is known to attack primary hydroxyl groups selectively, was used for the isolation of 1,2‐diacylglycerols from a mixture of diacylglycerols, hydroxyacylglycerols and sterols obtained from fresh milk. 1,2‐diacyl‐3‐tritylglycerols could be isolated, which were transformed into 1,2‐diacetyl‐3‐tritylglycerol. The stereochemical relation of this compound with respect to model compounds synthesized from serine showed that the predominating enantiomers of the 1,2‐diacylglycerols present in fresh milk have the sn‐1,2‐configuration. This provides additional evidence that these compounds are biosynthetic intermediates rather than lipolysis products.
The thermolysis of tetramethyl‐1,2‐dioxetane in degassed 1,4‐cyclohexadiene. Hydrogen abstraction by excited acetone
Authors: Bartlett Paul D. , Baumstark Alfons L. , Landis Michael E.
Published: September 2010

The thermolysis of tetramethyl‐1,2‐dioxetane (1) in degassed 1,4‐cyclohexadiene affords products attributable to hydrogen abstraction from solvent by excited acetone: benzene + 2‐propanol (.14–.15 moles each per mole 1), 1,4‐dihydrocumyl alcohol (2‐[2,5‐cyclohexadien‐1‐yl]‐2‐propanol) (.05 moles per mole 1), and a small amount of tetrahydrobiphenyls. These products are formed in the same proportions during the irradiation of acetone in degassed 1,4‐cyclohexadiene. The rate and kinetic order of the decomposition of 1 is the same as in air‐saturated solvents, where no acetone reduction products are observed. Comparison of the product yields with the known rate of quenching of acetone triplets by cyclohexadiene leads to the conclusion that at least one‐third of the quenching is of the nonreactive type, accompanying capture of allylic hydrogen from the hydrocarbon. The mechanism of the reaction is discussed, and a comparison is drawn between different radicals and anions in their modes of coupling with the cyclohexadienyl radical.
Formation of a biologically active complex from two complementary fragments of horse heart cytochrome‐c
Authors: Westerhuis L. W. , Tesser G. I. , Nivard R. J. F.
Published: September 2010

This report describes the formation of a non‐covalent complex between two tryptic peptides of horse heart cytochrome‐c. All amino functions of cytochrome‐c were completely protected with the methylsulfonylethyloxycarbonyl (Msc) group. Trypsin split the protected product specifically at Arg38. After separation the fragments were deprotected by a very short treatment with a base.

The complex resulting from the deprotected peptides, exhibited a completely developed 695 nm band, and an enhanced oxidase but diminished reductase activity in comparison with native horse heart cytochrome‐c.
Chemical effects of steric strains. Part XXIII. Steric effects as a factor in the stability of addition compounds of amines with 9‐borabicyclo[3.3.1]nonane
Authors: Brown Herbert C. , Wang Kung K.
Published: September 2010

An infrared technique was developed to establish the equilibrium involved in the reaction of 9‐borabicyclo[3.3.1]nonane with representative amines under standard conditions (25.0°C, cyclohexane or THF solution): (9‐BBN)2 + 2 Amine ⇌ 2 9‐BBN: Amine. Coordination is complete with primary amines, even as hindered as tert‐butylamine. It is complete with diethylamine, but incomplete with diisopropylamine. It is incomplete even with the simple triethylamine. However, the cyclic structure corresponding to triethylamine, namely, quinuclidine, forms a stable adduct. Pyridine is fully coordinated, but the extent of coordination decreases with increasing steric requirements of the 2‐alkyl substituent, becoming essentially zero with 2‐tert‐butylpyridine and 2,6‐dimethylpyridine. Thus the results with the unusual Lewis acid, 9‐borabicyclo[3.3.1]nonane parallel closely the earlier results for the stability of addition compounds produced by the reaction of such amines with trimethyl‐borane, boron trifluoride, and borane.
Some aspects of counter current dialysis through hollow fiber membranes
Authors: Hermans J. J.
Published: September 2010

A dilute solution flows through a bundle of parallel fibers, the wall of which is permeable to the solute. On the outside of the fibers, possibly in another solvent, the solution flows in the opposite direction. The mass balance equations are first solved for the limiting case of very large diffusivity, and the concentrations on either side of the membrane are found to be simple exponential functions of the axial coordinate. The role of diffusion can be accounted for in closed form if polarisation is not excessive, so that the velocity of the liquid may be replaced by its cross‐sectional average. In this case the exponential behavior remains the same except that the coefficient in the exponent becomes a function of the Sherwood number.
Hydrolysis of monomeric substrates by porcine pancreatic (pro)phospholipase A2. The use of a spectrophotometric assay
Authors: Volwerk J.J. , Dedieu A.G.R. , Verheij H.M. , Dijkman R. , de Haas G.H.
Published: September 2010

In the course of searching for specific chromogenic substrates which might be useful for the assay of phospholipase A2 at monomeric substrate concentrations, we tested short‐chain lecithin analogues in which the oxygen ester bonds were replaced by thio ester. Spectrophotometric measurement of the hydrolysis of the thio ester in the presence of 5,5′‐dithiobis(2‐nitrobenzoic acid) or di‐4‐pyridyl disulfide provides a continuous and sensitive assay.

Using this assay it was found that the zymogen expressed considerably higher enzymatic activities than phospholipase A2 which reinforces the conclusions of Pieterson et al. [Biochemistry 13, 1455 (1974)] that the zymogen, like the phospholipase, has a fully functional active site and that the fundamental difference between phospholipase A2 and the zymogen only becomes evident if the substrate is present in an organized lipid water interface.

The use of the spectrophotometric assay allowed a determination of the pH‐rate profile of both phospholipase A2 and its precursor. Phospholipase A2 shows an optimum at pH 8.5 whereas the maximal activity of the precursor remains constant between pH 6 and 9. Initial velocity patterns as a function of Ca2+ and substrate are consistent with a random addition of substrate and cofactor to the enzyme.
Structural effects in the intermolecular exciplex formation of 2‐methylnaphthalene and tertiary amines
Authors: Meeus F. , van der Auweraer M. , Dederen J.C. , de Schryver F.C.
Published: September 2010

The quenching rate constant of 2‐methylnaphthalene (2 MN) with triethylamine (TEA) and N‐methylpiperidine (NMP) in a polar protic solvent is found to be less than diffusion controlled. In a non polar solvent the exciplex stabilisation and entropy of formation indicate a tighter bound complex for the 2 MN‐TEA system than for 2 MN‐NMP. Both observations are interpreted as arising from geometric restrictions in the approach of the amine to the excited 2‐methylnaphthalene.
Hydrogen bonding of 5α‐cholestanol in carbon tetrachloride
Authors: Kunst M. , van Duijn D. , Bordewijk P.
Published: September 2010

Self‐association and complex formation with tetrahydrofuran has been studied for 5α‐cholestan‐3α‐ol and 5α‐cholestan‐3β‐ol in carbon tetrachloride, with the help of infrared measurements in the fundamental hydroxyl stretching range. For the self‐association the monomer/dimer/tetramer model was found to be appropriate, with dimerization constants that are equal to those for cholesterol, while for 5α‐cholestan‐3α‐ol the tetramerization constants are also equal to those for cholesterol, and for 5α‐cholestan‐3α‐ol they are somewhat higher.

With tetrahydrofuran 1/1 complexes were found, with equilibrium constants equal to the dimerization constants.
Kinetics of the gas‐phase ammoxidation of toluene to benzonitrile on a Bi‐Mo‐O catalyst
Authors: den Ridder J. J. J. , van Ingen H. W. T. J. , van den Berg P. J.
Published: September 2010

For the selective gas‐phase ammoxidation of toluene on a Bi‐Mo‐O catalyst a kinetic model has been developed in which the combustion of ammonia and benzonitrile has been taken into account. The effect of steam has been investigated. Temperature in the 640‐750 K region has hardly any effect on the selectivity to nitrile, which is maximal at 83%. Values are given for the rate parameters of main and side reactions.
Photochemistry of aromatic nitro compounds, XIII. Photoreduction of sterically hindered nitrobenzenes in aliphatic amines
Authors: Döpp Dietrich , Müller Dietmar
Published: September 2010

Photolysis of sterically hindered nitrobenzenes (1a‐d) in tertiary aliphatic amines as solvents results in efficient photoreduction to hydroxylamine derivatives and/or the corresponding anilines. Quantum yields for conversion of starting material Φconv in triethylamine have been determinded for 1a, c, d to be 0.47, 0.25 and 0.39, respectively, whereas with diethylamine, Φconv ≈︁ 0.09. Support for an electron transfer mechanism of photoreduction in the cases reported here comes from the fact that 1a‐d do not undergo hydrogen transfer photoreduction and from the small isotope effect (kH/kD ≈︁ 1.1) when 1,1‐dideuterio‐triethylamine is used as solvent. A rationale for the formation of several nitrones as products of photolysis of 1a‐c in various tertiary amines is given.
Ionization and mutarotation of hexoses in aqueous alkaline solution as studied by 13C NMR spectroscopy
Authors: de Wit G. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

A 13C NMR spectroscopic study of glucose, mannose and fructose in aqueous alkaline solution has been carried out. Some of the 13C resonances are found to shift substantially with increasing pH. The 13C NMR titration curves allow of the determination of both the pKa values of the hexoses and the differences in acid strength of the α/β‐anomeric forms.

The shifts observed cannot be explained by a simple ionization; the ionized species is considered either as a rapid equilibrium between cyclic and pseudo‐cyclic ionized species or as a non‐classical anion. It is concluded that base catalysis in the mutarotation reaction originates from a weakening of the ring C‐O bond in the generated sugar anion.
A formalism for the classification and design of organic reactions. II. The classes of (+ −)n + and (− +)n − reactions
Authors: Arens J. F.
Published: September 2010

The coding system proposed in the previous paper is extended to reactions involving an odd number of atoms, one of which is coordinatively unsaturated. This atom can extend its bonding with two units. Chelotropic reactions fit into this class characterized by operators (+ ‐)n +. Reactions in the reversed direction (operator (‐ +)n‐) are equally important. The coding system allows the design of new reactions.
Phase transitions in solids, studied by adiabatic calorimetry. I. Design and test of an automatic adiabatic calorimeter
Authors: Schaake R. C. F. , Offringa J. C. A. , van der Berg G. J. K. , van Miltenburg J. C.
Published: September 2010

The construction of an automatic adiabatic calorimeter is described. A block diagram is given of the data‐logging system used. n‐Heptane is used to check the performance of the apparatus.