bluuebunny/crossref_metadata_2025 huggingface dataset:
Alkenesulfonic acids: PMR spectra and rates of base‐ and acid‐catalysed double‐bond isomerization and hydrogen‐deuterium exchange reactions
Authors: Brouwer D. M. , van Doorn J. A.
Published: September 2010

Proton magnetic resonance spectra of a number of simple alkenesulfonic acids and related hydroxyalkanesulfonic acids have been measured. The compound described in the literature as 2‐methylpropene‐1,3‐disulfonic acid (I) has been found to be 2‐methylenepropane‐1,3‐disulfonic acid (II). Interconversion of I and II and of the 1‐ and 2‐propene‐1‐sulfonic acids can be effected at 100° in 1N‐sodium hydroxide as well as concentrated sulfuric acid. The equilibration of 2‐propene‐1‐sulfonic acid and the hydrogen sulfate of 2‐propanol‐1‐sulfonic acid in sulfuric acid is much faster than the equilibration of these two compounds with 1‐propene‐1‐sulfonic acid and is thought to involve intramolecular catalysis. Double‐bond isomerization of 2‐methyl‐2‐propene‐1‐sulfonic acid can only be effected under alkaline conditions since this compound reacts rapidly with sulfuric acid to give eventually the disulfonic acids.

Equilibrium constants for isomeric α,β‐ and β,γ‐unsaturated sulfonic acids are reported. The base‐catalysed isomerizations are much slower than the hydrogen‐deuterium exchange of the α‐hydrogens; the rate of acid‐catalysed exchange of both types of hydrogens in II is about the same as that of the double‐bond migration.
Optical rotatory dispersion and circular dichroism of prostaglandins
Authors: Korver O.
Published: September 2010

Optical rotatory dispersion and circular dichroism data are given for eight prostaglandins. An interpretation of the data is given in terms of the conformation of the cyclopentanone ring.
The heptatrienyl anion and its electrocyclization to the cycloheptadienyl anion
Authors: Kloosterziel H. , van Drunen J. A. A.
Published: September 2010

NMR spectroscopy reveals that the reaction between hepta‐1,3,5‐triene and potassium amide yields the all‐trans heptatrienyl anion, which readily isomerizes to the cycloheptadienyl anion.
A note on the selective t‐butylation of benzene and alkylbenzenes
Authors: Baas J. M. A. , van Bekkum H. , Hoefnagel M. A. , Wepster B. M.
Published: September 2010

By alkylation of benzene with t‐butyl chloride in the presence of aluminium chloride, 1,4‐di‐ and 1,3,5‐tri‐t‐butylbenzene can be prepared in a simple manner. Several polyalkylbenzenes with one or more t‐butyl groups have been made readily accessible.
The ligand properties of hydroxypyridines: Part I. Hexakis(2‐pyridone) metal perchlorates and tetrafluoroborates
Authors: Reedijk J.
Published: September 2010

A number of solvates with the general formula M(PYDO)6(anion)2, is reported; in this formula M = Mg, Mn, Fe, Co, Ni, Cu, Zn, and Cd; PYDO = 2‐pyridone, the anion ClO4− or BF4−. Further Ca(PYDO)8(ClO4)2 and Al(PYDO)6(ClO4)3 are described.

The compounds are characterized by chemical analyses and a number of physical measurements. The ligand PYDO appears to coordinate to metal ions via the lone pair of electrons of the C  O link, with the ligand in the lactam form.

Metal‐ligand stretching frequencies are observed in the 250‐400 cm−1 region. The ligand PYDO is placed in the spectrochemical and nephelauxetic series from ligand‐field spectra. These spectra also indicated the presence of octahedral ions M(PYDO)62+ in the solvates. Only the copper compounds are not octahedrally coordinated, as concluded from infrared spectra, X‐ray powder diagrams and paramagnetic resonance measurements. The magnetic moments of the transition‐metal compounds are also in the range for octahedrally surrounded metal ions.
Electron diffraction by gases: The molecular structures of cis‐ and trans‐4‐tert‐butyl‐1‐chlorocyclohexane
Authors: Dallinga G. , Toneman L. H.
Published: September 2010

The structures of cis‐ and trans‐4‐tert‐butyl‐1‐chlorocyclohexane have been determined by means of electron diffraction of the vapour. The differences in length between carbon‐carbon bonds and between axial and equatorial carbon‐chlorine bonds are compared with the results of extended Hückel MO calculations.
Conformation of non‐aromatic ring compounds: Part 55. Dipole moments, NMR spectra and conformation of trans‐2,3‐dihalogenotetralins
Authors: Buys H. R. , Leeuwestein C. H. , Havinga E.
Published: September 2010

The conformational equilibria in trans‐2,3‐dihalogenotetralins are studied with the aid of dipole moments and NMR spectroscopy. It is concluded that the diaxial conformer strongly predominates in solution. From the combination of dipole moment and NMR data the thermodynamic quantities ΔH0 and ΔS0 are calculated for the dichloro compound. A comparison is made with the results obtained earlier for other vicinal dihalogeno compounds.
Microbiological transformation of 9β,10α‐steroids: Part IV. 9β‐hydroxylation by curvularia species
Authors: van der Slide D. , de Flines J. , van der Waard W. F. , Smit A.
Published: September 2010

Fermentation of 9β,10α‐androst‐4‐ene‐3,17‐dione, 9β,10α‐testosterone, 9β,10α‐progesterone and 21‐hydroxy‐9β,10α‐progesterone with Curvularia species gave rise to the 9β‐hydroxylated derivatives, together with some other products.
Electrochemical reduction of aza aromatics. Part III: Reaction rate constants of the mononegative ions of the di‐aza aromatics with water
Authors: van der Meer D.
Published: September 2010

The protonation rate constants of the mononegative ions of the di‐aza aromatics with water are obtained from the increase in the diffusion current of the first reduction wave on addition of water to the dimethylformamide (DMF) solution. The rate constant is obtained from an approximate derivation given by Hoijtink et al. and from an exact solution given by Nicholson et al. From the dependence of the half‐wave potential on the water concentration, it is shown that the difference between the solvation of the neutral molecules and the mononegative ions is highest for the smallest molecules. Quantumchemical calculations predict a high protonation rate constant for pyrimidine and quinazoline.
Some substitution reactions of thieno[3,4‐b]thiophene and methyl thieno[3;4‐b]thiophene‐2‐carboxylate
Authors: Wynberg Hans , Feijen J.
Published: September 2010

The formylation of thieno[3,4‐b]thiophene gives a mixture of 4‐formyl‐ and 6‐formyl‐thieno[3,4‐b]thiophene in a ratio of 70 : 30. Lithiation followed by formylation of the resulting organolithium compounds changes this ratio to 20 : 80. The formylation of methyl thieno[3,4‐b]thiophene‐2‐carboxylate has been shown to give the 4‐ and 6‐substituted isomers in a 50 : 50 ratio. The structures of the substitution products were established by oxidation and desulfurization experiments and by PMR spectroscopy.
Association constants of molecular complexes of aromatic hydrocarbons with aldehydes, ketones and some nitro‐aromatics
Authors: Foster R. , Twiselton D. R.
Published: September 2010

Association constants for complex formation between aromatic hydrocarbons and aldehydes and ketones in carbon tetrachloride solutions have been estimated from NMR proton chemical shifts. With acetone and other aliphatic ketones, there is indication of a weak interaction. In the case of some substituted benzaldehydes, the values of association constant obtained are dependent on the particular proton measured. A similar effect is observed in the complexes of 2,4,6‐trinitroanisole and of 2,4,6‐trinitrotoluene. The anomalous behaviour can possibly be accounted for if a 2: 1 complex as well as 1: 1 complex is present. Alternatively the results could be explained by a 1: 1 complex (or series of 1: 1 complexes) in which the overall chemical shift of the measured nucleus in the pure complex (or complexes) is concentration dependent.
The crystal and molecular structure of pethidine hydrobromide
Authors: van Koningsveld H.
Published: September 2010

The crystal structure of pethidine hydrobromide was determined by X‐ray analysis, using the heavy atom technique.

The crystals are monoclinic, space group P21/c with four molecules of C15H22BrNO2 in the unit cell.

Contrary to Beckett's suggestion, the aromatic ring in the molecule is linked equatorially to the piperidine ring and is nearly coplanar with the C(3)‐C(2) bond. The distance between the methyl carbon atom, attached to the piperidine nitrogen and the most distant atom of the aromatic ring, C(6)‐C(4′), is 9.61 Å, whereas the corresponding distance in the morphine molecule is 6.75 Å.
Cyanate decomposition catalyzed by certain bivalent anions
Authors: Vogels G. D. , Uffink Lida , van der Drift C.
Published: September 2010

Ammonia production from cyanate was measured as a function of pH.

The kinetic description of the process included acid‐catalyzed hydrolysis of isocyanic acid and spontaneous hydrolysis of isocyanic acid and cyanate. These reactions were predominant at pH values below 2, between 3 and 8, and above 9, respectively.

The hydrolysis was strongly catalyzed by certain bivalent anions. The geometry of the anion appeared to be an important factor in the catalytic process, since carbonate, phosphate, succinate, maleate, citrate and phthalate were catalysts, whereas other bivalent anions, viz. sulfate, oxalate, fumarate and isophthalate, were without effect. Catalysis by bivalent anions was supposed to proceed via carbamoyl derivatives of the anions. The negatively charged group of the carbamoyl derivative was thought to cause an intramolecular general base‐catalyzed reaction.

The implications of this study for the mechanism of urease action were considered.
On the dependence of viscosity on temperature for liquids: A semi‐empirical treatise
Authors: Fieggen W.
Published: September 2010

In this communication we introduce the viscosity‐temperature relation for liquids

which actually contains four independent constants. The equation is applied to literature data for water, ethanol, n‐butyric acid, aluminium isopropoxide, n‐octane, n‐eicosane, toluene and n‐decylbenzene. The mean error between observed and calculated viscosity values for the entire liquid range varies from 0.06% for n‐octane to 0.8% for toluene.

The equation is derived in an approximate way from the rate‐theory approach of Eyring, in which the liquids are assumed to have a quasi‐crystalline structure. We take into account a thermal expansion of the lattice, which influences the activation energy for viscous flow. The calculated values of the parameters are consistent with their physical meaning, with a possible exception for aluminium isopropoxide. The restrictions imposed by the theoretical model are discussed.
Iso‐anellated thienopyrroles: The chemistry of 5,6‐dihydro‐4H‐thieno[2,3‐c]pyrroles and 5H‐thieno[2,3‐c]pyrroles
Authors: Feijen J. , Wynberg Hans
Published: September 2010

The ring closure reaction of methyl 2,3‐bis(chloromethyl)thiophene‐5‐carboxylate with several primary amines gives a series of 5,6‐dihydro‐4H‐thieno‐[2,3‐c]pyrroles. Oxidation of some of these dihydro compounds, using aqueous hydrogen peroxide in methanol, furnishes the corresponding N‐oxides. When the nitrogen atom possesses an aromatic substituent and the oxidation is carried out with aqueous hydrogen peroxide in formic acid, Meisenheimer
1 rearrangement products instead of N‐oxides are formed. The structure of one of the Meisenheimer products was elucidated by an independent synthesis of its degradation product.

5H‐Thieno[2,3‐c]pyrroles are prepared by three separate methods: (a) dehydration of the N‐oxides; (b) autoxidation of the dihydrothieno[2,3‐c]‐pyrroles; (c) dehydrogenation of the dihydro compounds with chloranil.
Proton magnetic resonance studies of specifically deuterated cyclohexane compounds. Part I.: Cyclohexane and Methylcyclohexane
Authors: Remijnse J. D. , van Bekkum H. , Wepster B. M.
Published: September 2010

The preparation of a specifically deuterated cyclohexane and some methyl‐cyclohexanes by selective cis‐addition of hydrogen to perdeuterated cyclohexene and 1‐, 3‐, and 4‐methylcyclohexene is reported. The deuterium decoupled proton magnetic resonance spectra of these compounds are analyzed. The magnitude of the deuterium isotope effect is determined. The coupling constants show that no ring distortion is caused by the equatorial methyl group. There is an anomalous shift to higher field of the axial ring protons vicinal to the equatorial methyl group. This explains the absorptions at exceptionally high field observed for some di‐ and tri‐methylcyclohexanes.
Chemistry of Sulfines. Part VIII: Synthesis and reactions of chlorosulfines
Authors: Zwanenburg B. , Thijs L. , Strating J.
Published: September 2010

The preparation of the chlorosulfines RC(Cl)=S=O where R is C6H5 and C6H5S, by oxidation of the corresponding thioacyl chlorides, is described. Reaction of these chlorosulfines with thiophenol and potassium thiocyanate leads to substitution of the chlorine atom giving phenylthio‐ and thiocyanosulfines, respectively. The displacement of the chlorine atom in chloro‐phenylsulfine by the phenylthio group occurs stereospecifically: the geometrical configuration of the chlorosulfine is predominantly retained in the product. A mechanism for these displacement reactions is proposed.
C‐Nitroso compounds. Part XVI: The reaction of C‐nitroso compounds with benzenesulfinic acid. An ESR study of alkyl and aryl benzenesulfonyl nitroxides
Authors: Wajer Th. A. J. W. , Geluk H. W. , Engberts J. B. F. N. , de Boer Th. J.
Published: September 2010

During the reaction of aliphatic and aromatic C‐nitroso compounds (RNO) with benzenesulfinic acid, ESR spectra of alkyl and aryl benzenesulfonyl nitroxides (aN about 12 gauss, g = 2.0060) have been observed. Unequivocal evidence for the structure R(C6H5SO2)NO* is found in an independent preparation in situ by oxidation of N‐alkyl‐ or N‐aryl‐benzenesulfonylhydroxylamines.

Sulfonyl nitroxides are also generated by photolysis of N‐methyl‐N‐nitrosotosylamide in hydrocarbons containing abstractable hydrogen atoms.

A possible explanation for the rather large nitrogen hyperfine splitting constants of these nitroxides is discussed.
The photolysis of Cyclopropanecarbaldehyde at 254 nm
Authors: Overwater J. J. I. , Cerfontain H.
Published: September 2010

Cyclopropanecarbaldehyde has been photolyzed in the gas phase with light in the 254 nm region. The most important gaseous products are carbon monoxide, ethene, propene and cyclopropane.

The quantum yield of propene, which is almost independent of temperature, decreases with increasing aldehyde pressure but increases with increasing intensity of the absorbed light. The ratio of the yields of ethene and propene is independent of aldehyde pressure and absorbed light intensity, but increases with increasing temperatures. The quantum yield of cyclopropane increases both with increasing temperatures and increasing aldehyde pressure, but decreases with increasing absorbed light intensity.

It is suggested that ethene and propene are formed by intramolecular decomposition from the same singlet excited state, whereas cyclopropane results from a radical decomposition of triplet aldehyde. The influence of the absorbed light intensity on the quantum yields of the gaseous products is explained in terms of triplet‐triplet annihilation.
Synthesis of 3,5‐Dihydroxy‐2‐Methyl‐5,6‐Dihydropyran‐4‐one from Aldohexoses and Secondary Amine salts
Authors: van den Ouweland G. A. M. , Peer H. G.
Published: September 2010

3,5‐Dihydroxy‐2‐methyl‐5,6‐dihydropyran‐4‐one was prepared in reasonable yield from D‐glucose and piperidine salts. Of the possible mechanisms, experimental evidence favours that involving conversion of the resulting aldosylamine into the enol of the corresponding aminodeoxyketose (Amadori rearrangement), followed by 1,4‐elimination of amine from this enol and subsequent acid‐catalysed cyclization.
The s‐trans‐conformation of 2‐thienyl‐carbonyl compounds
Authors: Kaper L. , de Boer Th. J.
Published: September 2010

2‐Thienyl‐carbonyl compounds occur exclusively in the s‐trans conformation as follows from NMR solvent shifts, temperature dependence of NMR spectra and nuclear Overhauser effects (NOE) as observed in some appropriately substituted 2‐thienyl‐carbonyl compounds. IR spectra are also in agreement with one (s‐trans) conformation.
Adducts of thiophosphoryl compounds with metal halides. Part III: Addition compounds of phosphoryl bromide and thiophosphoryl bromide
Authors: van der Veer W. , Jellinek F.
Published: September 2010

The addition compounds Br3PS · AlBr3, Br3PS · SbCl5 and Br3PS · SO3 were prepared and their thermal decomposition studied. The adduct Br3PS · AlCl3, unstable at room temperature, was found as an intermediate in the reaction of AlBr3 with PSCl3. The first steps of the decomposition of Br3PS · SbCl5 involve exchange of the halogens between P and Sb; finally, PSCl3, SbCl3, SbBr3 and bromine are formed. The decomposition of Br3PS · SbCl5 at elevated temperatures, however, gives PCl5 · SbCl5, SbBr3, PSBr3 and sulfur. Br3PS · SO3 decomposes at 10° to SO2, POBr3 and sulfur. The adducts Br3PO · AlBr3, Br3PO · 3 AlCl3, Br3PO · AlCl3, Br3PO · SbCl5, (Br3PO)2SbCl3, (Br3PO)2SbBr3, (Br3PO)2FeBr2, and Br3PO · 2 SO3 (?) were also prepared‐most of them for the first time‐and their thermal decomposition studied. Infrared spectra of the adducts of PSBr3 and POBr3 with metal halides show that the sulfur (or oxygen) atom is coordinated with the metal.
Studies on polypeptides. Part VIII: Synthesis of L‐ and D‐2,6‐diamino‐4‐hexynoic acid
Authors: Jansen A. C. A. , Kerling K. E. T. , Havinga E.
Published: September 2010

L‐ and D‐2,6‐Diamino‐4‐hexynoic acid were obtained in good yield by acylase I resolution of DL‐2,6‐diacetylamino‐4‐hexynoic acid. The latter compound was synthesized from 1,4‐dichloro‐2‐butyne via 1‐acetylamino‐4‐chloro‐2‐butyne and ethyl 2,6‐diacetylamino‐2‐ethoxycarboxyl‐4‐hexynoate. Catalytic hydrogenation of the title compounds yielded pure L‐ and D‐lysine. These analogues of lysine can be useful in the synthesis of 4,5‐deuterated or tritiated L‐ and D‐lysine.
Studies on polypeptides. Part XI: Fragment condensation by azide coupling with a polymer‐bound peptide. The synthesis of 1‐13[10‐Citrulline, 13‐Leucine] bovine pancreatic ribonuclease
Authors: Visser S. , Kerling K. E. T.
Published: September 2010

All‐L‐Nα, Nϵ‐di‐tbutoxycarbonyllysyl‐γ‐t‐butylglutamylthreonylalanylalanylalanyl‐Nϵ‐benzyloxycarbonyllysylphenylalanine azide was coupled to all‐L‐γ‐t‐butylglutamylcitrullylglutaminyl‐Nim‐benzyl histidylleucine bound on a solid support. The tridecapeptide obtained upon cleavage from the resin with hydrogen bromide in trifluoroacetic acid contained only a few percent of unreacted penta‐peptide and could easily be purified by gel‐filtration. No product resulting from a rearrangement of the azide to the isocyanate, followed by condensation with the pentapeptide‐resin, could be detected. Removal of the imidazole protecting group yielded the N‐terminal tridecapeptide of bovine pancreatic ribonuclease in which the arginine‐10 and the methionine‐13 residues have been replaced by citrulline and leucine, respectively.
Polynuclear heterocyclic systems: Part VII. Addition of dimethyl azodiformate to 1‐arylcycloalkenes
Authors: Willems A. G. M. , van Eck R. Ritsema , Nijhuis H. , Pandit U. K. , Huisman H. O.
Published: September 2010

The reaction of dimethyl azodiformate with 1‐phenylcyclopentene, 1‐phenylcyclohexene, 1‐(2‐naphthyl)cyclopentene, 1‐(2‐naphthyl)cyclohexene, 1‐(6‐methoxy‐2‐naphthyl)cyclopentene and 1‐(6‐methoxy‐2‐naphthyl)cyclohexene gives 2: 1 (ester‐olefin) adducts. The reaction mechanism of adduct formation is discussed.
The synthesis of 1‐tosylalkyl isocyanates and N(1‐tosylalkyl)carbamoyl chlorides from S‐ethyl N‐(1‐tosylalkyl) thiocarbamates
Authors: Olijnsma T. , Engberts J. B. F. N. , Strating J.
Published: September 2010

1‐Tosylalkyl isocyanates, p‐CH3C6H4SO2CHRNCO (II), have been prepared in good yields from the reaction of S‐ethyl N‐(1‐tosylalkyl)thiocarbamates (I) and chlorine in a heterogeneous mixture of dichloromethane and aqueous sodium hydrogen carbonate. The reaction probably involves the intermediate formation of the previously unreported N‐(1‐tosylalkyl)carbamoyl chlorides, p‐CH3C6H4SO2CHRNR′COCl (IV), which may be isolated in high yield under anhydrous reaction conditions. In mildly alkaline solutions, these carbamoyl chlorides (R′  H) are smoothly converted into the 1‐tosylalkyl isocyanates. Ethanesulfonyl N‐methyl‐N‐(tosylmethyl)formamide (V), obtained by oxidation of S‐ethyl N‐methyl‐N‐(tosylmethyl)thiocarbamate, p‐CH3C6H4SO2CH2N(CH3)C(O)SC2H5, with hydrogen peroxide in acetic acid, was treated with chlorine to give tosyl chloride and ethanesulfonyl chloride. α‐Oxosulfones, p‐CH3C6H4SO2CH2N(CH3)C(O)SO2C2H5, are therefore unlikely intermediates in the formation of N‐(1‐tosylalkyl)carbamoyl chlorides.

The reaction of S‐ethyl N‐(1‐tosylalkyl)thiocarbamates (I) with bromine in CH2Cl2/NaHCO3‐H2O in the presence of methanol gives methyl N‐(1‐tosylalkyl) carbamates, a result which can be best interpreted by assuming 1‐tosylalkyl isocyanates as intermediates.
The structure of the reduction product of the head‐to‐head photodimer of isophorone
Authors: Koning R. E. , Visser G. J. , Vos Aafje
Published: September 2010

An X‐ray diffraction study of the reduction product of the head‐to‐head photodimer of isophorone has shown that the six‐membered rings are in anti position relative to the four‐membered ring.
Functionalized enamines. Part VII: Reaction of dienamines with arenediazonium salts; Synthesis of 6,7‐diaza‐D‐homoequilenin methyl e her
Authors: Pollmann M. J. M. , Reus H. R. , Pandit U. K. , Huisman H. O.
Published: September 2010

The reaction of the dienamine (1) from 8a‐methyl‐1,6‐dioxo‐1,2,3,4,6,7, 8,8a‐octahydronaphthalene, with arenediazonium salts, has been investigated. Depending upon the solvent, β‐ as well as δ‐substituted products are obtained. A rationalization for this substitution pattern is proposed. The β‐substituted product, obtained upon reaction of 1 with m‐methoxybenzenediazonium fluoroborate, has been converted into 6,7‐diaza‐D‐homoequilenin methyl ether (13) in two simple steps.
Functionalized enamines. Part IX: Synthesis of fused furan systems via reaction of conjugated enamines with α‐halogenoketones
Authors: Pandit U. K. , Reus H. R. , de Jonge K.
Published: September 2010

Reaction of conjugated enamines with α‐bromoketones leads to the formation of substituted furans in one practical step. The reaction has been applied to the synthesis of steroido[3,4‐b]furans.
The molecular and crystal structure of an 11,13‐diaza‐estrone methyl ether hydrobromide
Authors: Joustra Anneke H. , Schenk H.
Published: September 2010

The crystals of a di‐aza steroid (C16H19N302 · HBr) which turned out to be 12‐amino‐11,13‐diaza‐9β, 14β‐11,12‐dehydroestrone methyl ether hydro‐bromide are monoclinic with cell dimensions a = 10.632, b = 10.667, c = 14.277 Å and β = 105.47°. The space group is P21/n. Z = 4. The hydrogen atoms of the asymmetric carbon atoms are all situated at the same side of the steroidal plane. This results in a cis‐coupling of the B/C junction. The B‐ and C‐rings are half chairs and the D‐ring is a Cs(15)‐envelope.
Nuclear magnetic resonance determination of association constants of electron donor — acceptor complexes: The effect of reference standards and the behaviour of mixed donors: (Short communication)
Authors: Foster R. , Twiselton D. R.
Published: September 2010

[1] It is shown experimentally that, for both 1H and 19F resonances, determinations of association constant can be independent of the reference standard.

[2] Mixtures of benzene and mesitylene behave in a simple additive manner in the presence of the electron‐acceptor fluoranil. This is analogous to the predicted behaviour of isomeric 1: 1 complexes formed between a single‐donor species with an acceptor in solution.
Addition of hydrogen halide to 1‐alkynylphosphines: Kinetics and mechanism
Authors: Borkent G. , Drenth W.
Published: September 2010

Addition of one molecule of hydrogen halide to the triple bond of 1‐alkynyl‐phosphines in aqueous solution is a trans reaction the rate of which is proportional to the activity of the halide ions. Rates of addition of HCl and DCl are approximately equal. The rate determining step involves addition of halide ion to protonated 1‐alkynylphosphine.
Ligand hyperfine structure in the EPR‐spectrum of the fluorochromyl(V)‐, and fluorotungstenyl(V)‐ions
Authors: van Kemenade J. T. C.
Published: September 2010

EPR spectra of the ions CrOF−5, MoOF−5 and WOF−5 in single crystals of suitable diamagnetic host compounds are given. All ligand hyperfine interaction parameters are measured and compared with values obtained from frozen glass spectra. Upon substitution, the paramagnetic ions are shown to make specific selections out of the three possible crystallografically unequivalent orientations.
Chemistry and spectroscopy in strongly acidic solutions. Part XXXIV: Interconversion of secondary and tertiary alkyloxocarbonium ions by decarbonylation‐carbonylation. Free‐enthalpy diagrams
Authors: Hogeveen H. , Roobeek C. F.
Published: September 2010

The secondary and tertiary oxocarbonium ions C5H11CO⊕ interconvert quite readily at room temperature in FHSO3/SbF5 (1: 1 m/m) solution by a process of decarbonylation, rearrangement and carbonylation. Consequently, starting from any secondary or tertiary carboxylic acid C5H11COOH, after initial dehydration, the same mixture of the four isomeric secondary and tertiary C5H11CO⊕ ions is obtained. From the free enthalpy of activation of the conversion of 2‐methylbutyl‐2‐oxocarbonium ion to 2‐methylbutyl‐3‐oxocarbonium ion (ΔG‡ = 21.2 kcal· mole−1 at 20°), combined with previously obtained free‐enthalpy data, the rate of carbonylation of secondary alkylcarbonium ions is calculated to be about 3.1071· mole−1· s−1 at 20°. In this process the carbonylation of the secondary alkylcarbonium ions is the slow step in the overall reaction.

The free enthalpy of activation of the conversion of sec. butyloxocarbonium ion to tert.butyloxocarbonium ion was found to be 30.4 kcal· mole−1 at 20°. Such a high value was anticipated in view of the relatively low rate of the rearrangement step sec.butyl cation → tert.butyl cation. This rearrangement is the slow step in the overall reaction.

Primary alkyloxocarbonium ions do not decarbonylate at temperatures up to 100°.
An improved synthesis of 4‐imidazoleëthanol
Authors: Bloemhoff W. , Kerling K. E. T.
Published: September 2010

An improved preparation of 4‐imidazoleëthanol [4‐(2‐hydroxyethyl)imidazole] (I) is described. Starting from 2‐butyne‐1,4‐diol (II), 4‐(2‐methoxyethyl)imidazole (III) has been obtained, which on cleavage with hydrobromic acid gives I in satisfactory overall yield. Prolonged heating of III in hydrobromic acid gives 4‐(2‐bromoethyl)imidazole hydrobromide.
Association constants of fluoranil‐methyl‐benzene complexes from nmr chemical shift measurements
Authors: Foster R. , Twiselton D. R.
Published: September 2010

The association constants for a series of methylbenzene‐fluoranil electron donor‐acceptor complexes have been determined from NMR chemical shift measurements using 1: 1 stoicheiometric ratios of electron donor‐electron acceptor. The resulting values differ from those obtained when large excess concentrations of donor are used. It is suggested that the differences may be the result of the presence of significant concentrations of termolecular complexes in the latter solutions.
Conformation of non‐aromatic ring compounds. Part 68. The calculation of dihedral angles from vicinal proton coupling constants in six‐membered ring compounds. Part 2
Authors: Buys H. R.
Published: September 2010

For six‐membered ring compounds having a −CH2‐CH2‐ fragment for which four vicinal coupling constants follow from the NMR spectrum (ABCD type), the ratio R = (Jtrans + J′trans/(Jcis + J′cis is equated to the ring torsional angle ψ in that fragment. The ψ values calculated from experimental coupling constants of trans‐2,3‐dichloro‐1,4‐dioxane (I) and ‐oxathiane (II), 2‐p‐chlorophenyl‐1,3‐dioxane (III), 2‐phenyl‐1,3‐dithiane (IV), trimethylene sulfite (V) and 2‐oxo‐2‐phenoxy‐1,3,2‐dioxaphosphorinane (VI) show an excellent agreement with the corresponding torsional angles obtained from X‐ray diffraction data.
Complexes with ligands containing the nitro group: Part III. Metal(II) nitrobenzene solvates
Authors: Driessen W. L. , van Geldrop L. M. , Groeneveld W. L.
Published: September 2010

Seven new complexes are reported with nitrobenzene as the ligand, viz. [M(C6H5NO2)6]2+[SbCl6]2− with M is Mg(II), Ca(II), Mn(II), Fe(II), Co(II), Ni(II), and Zn(II).

No shift in the NO stretching frequencies has been observed. The NO2 out of plane bending vibration shifts to higher frequencies dependent on the metal ions.

Investigation of ligand field spectra indicates the presence of octahedral species M(nitrobenzene)62+ in the solid compounds. Values for Dq and B for the Co and Ni compounds are reported.
Enthalpy of formation of liquid 1‐propanol by an improved combustion technique
Authors: Dekker H. , Mosselman C.
Published: September 2010

The enthalpy of formation of 1‐propanol at 298.15 K has been measured using an improved combustion technique.

A value of − 302.67 ± 0.25 kJ mole−1 was found.
Trans‐substitution and equilibration of phenols: Part I. Trans‐t‐butylation of phenols in the presence of aluminum phenoxide type catalysts
Authors: Willemse F.R.J. , Wolters J. , Kooyman E.C.
Published: September 2010

Phenols containing a free ortho‐position can be alkylated by ortho‐t‐butyl‐phenols in the presence of catalytic amounts of aluminium phenoxide at temperatures between about 120° and 170°.

Using 2‐t‐butylphenol, 2,6‐di‐t‐butyl‐phenol or ‐p‐cresol as the alkylating agent, trans‐t‐butylations were carried out with the following phenolic acceptors: phenol, o‐, m‐, p‐cresol, p‐Br‐, p‐Cl‐, p‐F‐, p‐CH3O‐, p‐t‐Bu‐, p‐isoPr‐, and p‐Et‐phenol. Higher rates were observed for the more acidic phenols.

The above mentioned reactions lead to equilibria of the type: 2,6‐di‐t‐butyl‐p‐Z‐C6H2OH + p‐Z‐C6H4OH ⇄ 2 2‐t‐butyl‐p‐Z‐C6H3OH

The equilibrium constant for this reaction is about 24 and independent of the substituent in the phenolic nucleus.

For Z = CH3 the energy of activation has the value 36 (± 3) kcal/mole.

When the 3, 4 and 5 positions are unoccupied, a slow ortho‐para isomerization takes place along with ortho‐trans‐t‐butylation.

The equilibrium between 2‐t‐butylphenol and 4‐t‐butylphenol lies far towards the thermodynamically more stable para‐isomer, the ortho‐isomer however is kinetically more favourable. Meta‐isomers are formed under these conditions to a small extent and only after long reaction times.

At temperatures above 140° some dealkylation occurs with formation of isobutene.

Both 3,5‐dimethylphenol and 2‐methoxyphenol failed to accept t‐butyl‐groups.
Investigations on sterols XXXVII: New routes to 9,10‐isomers of 6‐dehydroprogesterone
Authors: Rappoldt M.P. , Rix T.H.R.
Published: September 2010

The synthesis of 6‐dehydro‐9β, 10α‐progesterone (IV) from progesterone via irradiation of 3,20‐bis(ethylenedioxy)pregna‐5,7‐diene (II) is described. An analogous synthesis has been accomplished via 3‐(ethylenedioxy)pregna‐5,7‐dien‐20‐one (VI).

Pyrolysis of the 9,10‐seco‐bisacetal (IX), a vitamin D analogue, followed by hydrolysis and isomerization, gave the 8α,10α‐isomer of 6‐dehydroprogesterone (XI).
The crystal structure of MnNb4S8
Authors: Anzenhofer K. , de Boer J.J.
Published: September 2010

Using X‐ray reflection intensities collected with a single crystal, the crystal structure of MnNb4S8 has been determined. The position of Mn is uniquely defined. The difficulties arising in space group determination and crystal structure refinement are discussed in some detail; the most essential structural features are presented and compared with those of MnNb3S6.
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (XX): Pyrimidines (XXII). Conversion of some 5‐substituted 4‐chloro‐2‐phenyl‐pyrimidines into open‐chain compounds by potassium amide in liquid ammonia
Authors: van Meeteren H.W. , van der Plas H.C.
Published: September 2010

5‐Methoxy‐, 5‐ethoxy‐, 5‐methylthio‐ and 5‐phenyl‐ 4‐chloro‐2‐phenyl‐pyrimidines are transformed into open‐chain products by reactions with potassium amide in liquid ammonia at — 33°. The mechanism of this reaction has been elucidated with help of 14C‐labelled pyrimidines. It is demonstrated that the amide ion attacks C(6) of the pyrimidine nucleus and causes fission of the C(5)‐C(6) bond.
Reduction of alkyl‐substituted benzoic acids with lithium in liquid ammonia: Synthesis of 1‐alkyl‐2,5‐cyclohexadiene‐1‐carboxylic acids
Authors: van Bekkum H. , van Den Bosch C. B. , van Minnen‐Pathuis G. , de Mos J. C. , van Wijk A. M.
Published: September 2010

The reduction of alkyl‐substituted benzoic acids with lithium in liquid ammonia has been investigated. Without added proton donor the aromatic acid yields a dianion which can either be protonated with ammonium chloride or alkylated to give the corresponding 1,4‐dihydrobenzoic acid and 1‐alkyl 2,5‐cyclohexadiene‐1‐carboxylic acid, respectively.

In the presence of ethanol, 3‐ and 4‐alkylbenzoic acids yield either 1,4‐dihydro or 4,5‐dihydro products depending on the working up procedure Benzoic acid behaves similarly. Water is shown to be a useful proton donor in the reduction of 3‐ and 4‐alkylbenzoic acids to 1,4‐dihydro products. 2‐Alkylbenzoic acids yield 1,4‐dihydro products, irrespective of the experimental procedure.

Experiments with 4‐deuterobenzoic acid show the first proton addition to be irreversible in ammonia as well as in ammonia‐ethanol.

Some thirty new alkyl‐ and dialkyl‐cyclohexadienecarboxylic acids are described.
Preparation and Hofmann degradation of 1,1′‐dimethyl‐2,2′‐bis(trimethylammonio)‐bicyclopropyl dihydroxide
Authors: de Wolf W. H. , Bickelhaupt F.
Published: September 2010

1,1′‐Dimethyl‐2,2′‐bis(trimethylammonio)bicyclopropyl dihydroxide (XIb) was synthesized from 2,3‐dimethylbutadiene and methyl diazoacetate via several difunctional 1,1′‐dimethylbicyclopropyl derivatives. Hofmann degradation of XIb yielded ∼7% of a xylene mixture [o : (m + p) = 10 : 1], together with 2,2′‐bis(dimethylamino)‐1,1′‐dimethylbicyclopropyl (X), 3‐[2‐(dimethylamino)‐1‐methylcyclopropyl]‐3‐methylcyclopropene (XII) and 1‐(3‐butynyl)‐2‐(dimethylamino)‐1‐methylcyclopropane (XIII). The possible intermediacy of 1,1′‐dimethylbicyclopropenyl (I) is briefly discussed.
The cause of the medium effect upon the rate of the electron‐exchange reaction between iron(II) and iron(III)
Authors: Gelsema W. J. , Vink H. A.
Published: September 2010

The iron(II)‐ iron(III) electron‐exchange rate has been measured at 0° in aqueous perchloric acid‐sodium perchlorate and perchloric acid‐lithium perchlorate mixtures of varying acid concentration, at three values of the ionic strength.

The medium effects upon the rate of this reaction are interpreted as a result of a) the displacement of hydrolysis equilibria with the hydrogen ion concentration, and participation of the hydrolyzed ions in the exchange reaction, and b) the variation of the activity coefficients of the reacting species with the hydrogen ion concentration.
Dynamic Jahn‐Teller effect in the excited state of TeCl62−. √T dependence of the splitting of the C absorption band
Authors: Stufkens D. J. , Schenk A.
Published: September 2010

An investigation is reported on the temperature dependence of the splitting of the C‐band (1A1g → 1T1u) in the electronic absorption spectrum of TeCl62−. The splitting appears to be linearly dependent on the square root of temperature.

This behaviour proves the correctness of our previous assumption 1 about the dynamic character of the splitting.
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (XXI): Conversion of 2‐chloropyrazine into imidazole and 2‐cyanoimidazole by potassium amide in liquid ammonia
Authors: Lont P. J. , van Der Plas H. C. , Koudijs A.
Published: September 2010

By treatment with potassium amide in liquid ammonia, 2‐chloropyrazine is converted into a mixture of 2‐cyanoimidazole, imidazole and 2‐aminopyrazine. The mechanism of the formation of the two ring‐contracted products is discussed.
A study on the effect of labelling on the solubility of cerium(III) oxalate in water: On the feasibility of the radiometric determination of solubility
Authors: Gelsema W. J. , Remijnse A. G.
Published: September 2010

The solubilities of cerium(III) oxalate, both inactive and labelled with 144Ce, in water at 25°, have been determined by chemisorption on cation exchange paper followed by X‐ray fluorescence analysis of the paper and proved to be identical within experimental error.

The specific count rates of labelled cerium(III) oxalate in a saturated solution and in a standard solution in hydrochloric acid proved to be identical within experimental error.

These results, which are in contrast with those of Spitsyn et al., demonstrate once more, the validity of the radiometric method for the determination of solubility.

The solubility of anhydrous cerium(III) oxalate in water at 25° is 3.11 ± 0.16 mg · I−1.
Studies in the C8H8 field. Formation of Endo‐6‐ethynylbicyclo[3.1.0]hex‐2‐ene by gas‐phase photolysis of a carbon suboxide/bicyclo[2.2.1]hepta‐2,5‐diene mixture: (Short Communication)
Authors: Klumpp G.W. , van Dijk P.M.
Published: September 2010

The formation of endo‐6‐ethynylbicyclo[3.1.0]hex‐2‐ene (V) by gas‐phase photolysis of a carbon suboxide/bicyclo[2.2.1]hepta‐2,5‐diene mixture is described and possible reaction mechanisms are discussed.
Structure and physical properties of aluminium alkoxides. Part III: Vibrational spectra of aluminium isopropoxides
Authors: Fieggen W. , Gerding H.
Published: September 2010

Raman and infrared spectra of aluminium isopropoxide in some liquid and solid forms occurring at room temperature have been investigated. The depolarization ratio of Raman lines has been measured for the liquid.

The vibrational spectra are consistent with the occurrence of two molecular forms. In the freshly heated liquid and in the solid melting at 29.5°, probably a trimer is present. The vibrational spectra of this form and of dimeric Al‐t‐butoxide differ distinctly in the range 0‐750 cm−1. In the aged liquid and in the solids melting at 118° or about 137° a partially six‐coordinated tetramer, as proposed by Bradley, is the more probable molecular species.
Chemistry of α‐diazosulfones, XIII: Reaction of p‐tolylsulfonyldiazomethane or ethyl diazoacetate with sulfuryl chloride and various ethers
Authors: Middelbos W. , Zwanenburg B. , Strating J.
Published: September 2010

p‐Tolylsulfonyldiazomethane and ethyl diazoacetate react smoothly with sulfuryl chloride and various ethers (Tables I and II) producing α‐alkoxy‐α‐chloro‐sulfones and α‐alkoxy‐α‐chloroacetates in good yields. The reaction is proposed to proceed via a nucleophilic reaction of the ether with the diazonium ion XCH(Cl)N2⊕ (where X is p‐CH3C6H4SO2‐or C2H5OOC‐) which is formed by an electrophilic reaction of Cl⊕ (from SO2Cl2) with the diazo compound XCHN2. Subsequent scission of the ether linkage in the intermediate oxonium ion occurs upon attack of chloride ion. Chlorine and tert‐butyl hypochlorite can also be used as electrophilic reagents. Evidence for an ionic mechanism was provided by the reaction of cyclohexene with cyclic ethers and sulfuryl chloride which produces 1‐chloro‐2‐(ω‐chloroalkoxy)cyclohexanes.
Thermolytic reactions of esters. Part V: Thermal stability of diallyl oxalate vapour; reactivity of allyl radicals
Authors: Louw R.
Published: September 2010

Diallyl oxalate (DAO) vapour‐in an excess of toluene at atmospheric pressure and at 380‐510° ‐decomposes initially, homogeneously and in a first order process, giving carbon dioxide and allyl radicals; its half life is 20 minutes at 400°. DAO is thus found to be much more stable than was inferred from recent low temperature work by James and Kambanis5. It is concluded that the latter decomposition, in contrast with that in our hands, occurs at the wall of the reactor.

Apart from dimerizing, allyl radicals abstract hydrogen from toluene; the rate constant for this metathesis has been calculated and compared with literature data. Finally it is outlined that metathetical reactions R· + R′H → RH + R′·, involving allylic or benzylic groups R, R′ will proceed with activation energies of well below 20 and presumably of about 16 kcal. mole−1.
The Coordination chemistry of hexamethylphosphoramide
Authors: de Bolster M. W. G. , Groeneveld W. L.
Published: September 2010

A number of new solvates and adducts containing hexamethylphosphoramide is reported. The solvates have the general formula M{[(CH3)2N]3PO}4 2+(anion)22−, in which M = Mg, Ca, Sr, Mn, Fe, Co, Ni, Zn and Cd and the anions are BF4−, ClO4− and B(C6H5)4−. The adducts have the general formula M(anion)n {[(CH3)2N]3PO}m, in which M = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Al, Cr, Fe, Mo, n = 1 − 3, m = 1/2 − 5 and the anions are Cl−, Br−, I−, NO3−, NCS−, CH3COO− and SO42−.

The compounds are characterized and identified by chemical analysis and physical measurements.

Infrared spectra in the region 4000‐200 cm−1 have been investigated. The shift towards lower wave numbers in the P‐O stretching frequency and towards higher wave numbers in the P‐O bending frequency of the complexes is discussed. It is concluded, as has been suggested by other workers, that coordination takes place via the oxygen atom. A tentative assignment for the other ligand bands is proposed.

Ligand‐field spectra for the complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Cr(III) and Mo(III) have been investigated. Adapted values for Dq and B are reported and the ligand is placed in the spectrochemical and nephelauxetic series.

In agreement with results obtained by other workers it is concluded that if the anions are present as uncoordinated ions, or participate in the coordination as monodentate ligands, hexamethylphosphoramide has a tendency to form tetrahedrally surrounded complexes. With potential polydentate anions octahedrally surrounded cations are mostly found.
The molecular and crystal structure of N,N‐dimethyl‐p‐bromocinnamamide
Authors: Meester Marthie A. M. , Schenk H.
Published: September 2010

Crystals of N,N‐dimethyl‐p‐bromocinnamamide are triclinic of space group P1p̄, Z = 2, cell constants a = 7.686, b = 12.325, c = 5.850 Å, α = 83.98, β = 81.27 and γ = 94.23°.

The plane of the CO‐N(CH3)2‐group is rotated 15° out of the s‐cis conformation with respect to the rest of the conjugated system.
Hydride transfer reactions of the adamantyl cation (IV): Synthesis of 1,4‐ and 2,6‐substituted adamantanes by oxidation with sulfuric acid
Authors: Geluk H. W. , Schlatmann J. L. M. A.
Published: September 2010

The oxidation of adamantane by fuming sulfuric acid to 1,3‐, 1,4‐, and 2,6‐dihydroxyadamantane is discussed. The reactions are considered as hydride transfers from the adamantane nucleus to the acid. A synthetic procedure for 2,6‐adamantanedione and 5‐hydroxy‐2‐adamantanone is described.
The conversion of A Δ5‐14α‐ to a Δ5‐14β‐steroid oxidation of 3β‐acetoxy‐5α,6β‐dichloroandrostan‐17‐one by chromic anhydride
Authors: Jacobs H. J. C. , Bos M. G. J. , Hol C. M.
Published: September 2010

3β‐Acetoxy‐14β‐androst‐5‐en‐17‐one (7b) has been prepared in five steps from its 14α‐isomer 1. The influence of water on the chromic anhydride oxidation of 3β‐acetoxy‐5α,6β‐dichloroandrostan‐17‐one (2) in acetic acid has been investigated. The yield of 14α‐hydroxy‐derivative 3 is maximal if 2 to 3% of water is present in the reaction mixture.
Mixed carboxylic anhydrides: Part IX. Synthesis of alkyl thiolformates
Authors: Bax P. C. , Holsboer D. H. , van Der Veek A. P. M.
Published: September 2010

Base‐catalysed esterification of alkanethiols with formic acid/acetic anhydride reaction mixtures (F.A.M.2) affords pure thiolformates. The method for the preparation of pure aryl thiolformates3 could not be applied satisfactorily to alkyl thiolformates. Change of reaction temperature and amount of catalyst resulted in the desired improvements.
Synthesis of thyrotropin‐releasing hormone pyroglutamyl‐histidyl‐proline amide
Authors: Beyerman H. C. , Kranenburg P. , Syrier J. L. M.
Published: September 2010

The solid‐phase synthesis by a programmed mechanical synthesizer is described of L‐pyroglutamyl‐Nim‐benzyl‐L‐proline‐on‐polymer, PGA‐His(BZL)‐Pro‐P. Tertiary amine‐catalysed methanolysis split the peptide from the resin as PGA‐His(BZL)‐Pro‐OMe. The benzyl group was removed by hydrogenolysis in the presence of Pd/C. The peptide ester thus obtained could be converted by diethylene glycol‐catalysed ammonolysis into L‐pyroglutamyl‐L‐histidyl‐L‐proline amide. The method constitutes a practical synthesis of the said tripeptide amide, the thyrotropin‐releasing hormone (TRH) which was recently discovered.
6α‐ and 6β‐methyl steroids in the 19‐nor series
Authors: Bolt C.C. , van Den Broek A.J. , Visser G. Heijmens , de Jongh H.P. , Siegmann C.M.
Published: September 2010

The dehydration‐epimerization reaction applied to a 5α‐hydroxy‐6β‐methyl‐3‐oxo‐19‐nor‐steroid, under acid conditions, leads to a mixture of the 6α‐methyl‐3‐oxo‐Δ4‐19‐nor‐steroid and its 6β‐epimer. This is in contrast to the normal steroid series, in which exclusively the 6α‐methyl epimer is formed. A complete conversion to the 6α‐methyl compounds can be achieved by alkaline hydrolysis of the corresponding 3‐acetoxy‐6‐methyl‐Δ3,5 compounds.

Several 6‐methyl‐3‐oxo‐Δ4 compounds in the estrene and 19‐nor‐pregnene series have been converted to their 3‐desoxo derivatives.
Vibrational spectrum of trimethylsulfonium bromide
Authors: Ypenburg J.W. , van Der Leij‐Van Wirdum E. , Gerding H.
Published: September 2010

Trimethylsulfonium bromide (CH3)3SBr has been prepared; melting range 183‐186°C. Infrared absorption and Raman spectra have been recorded and assigned.
Photochemical reactions of N‐substituted‐N‐nitrososulfonamides: C‐ and N‐nitroso compounds. Part XX (Short Communication)
Authors: Engberts J.B.F.N. , van Der Laan L.C.J. , de Boer Th. J.
Published: September 2010

Irradiation of the N‐alkyl‐N‐nitroso‐p‐toluenesulfonamides C7H7SO2N(NO)‐CHRR′ (Ia‐Ig) with UV light either in anhydrous CH3OH, or in moist CFCl3 or n‐hexane at ‐ 30° leads to an N‐alkyl cleavage reaction, affording, after aqueous work‐up, p‐toluenesulfonamide and the carbonyl compound RCOR′ in high yield. Nitrous oxide was a third reaction product. A possible route via sulfonylimines, C7H7SO2NCRR′, is indicated.
Reactions of hydroxycarbonium ions in strong acids IV: Kinetics of the rearrangements of protonated aldehydes and ketones
Authors: Brouwer D. M. , van Doorn J. A.
Published: September 2010

A systematic study has been made of the kinetics of the rearrangements of protonated dialkyl ketones, aldehydes and α‐deuterated aldehydes. The rearrangements can be divided into four groups, the relative rates of which, at 25°, are approximately 107: 102: 102: 1, viz. (i) of α‐dibranched aldehydes to α‐mono‐branched ketones, (ii) of α‐monobranched aldehydes to di‐n‐alkyl ketones, (iii) of α‐dibranched ketones, (iv) of α‐monobranched ketones.

Whereas the first three groups of reactions proceed by a two‐step process (1,2‐alkyl and/or hydrogen shifts via an α‐hydroxyalkyl carbonium ion), the interconversion of α‐monobranched ketones takes place by a four‐step process via tertiary α‐hydroxyalkyl carbonium ions and a protonated α‐dibranched aldehyde.

The intramolecular exchange of α‐D and carbonyl‐H in deuterated isobutyraldehyde and propionaldehyde is about ten times slower than the rearrangements under (i) and (ii), respectively. This is due to the lower stability of the intermediate α‐hydroxyalkyl carbonium ions in the former two reactions; intrinsically, hydrogen shifts are faster than alkyl shifts. Other things being equal, the ethyl shift is about four times faster than the methyl shift.

Protonated aldehydes are about 9 kcal.mole−1 less stable than the isomeric protonated ketones, which is mainly due to the difference in stability of the unprotonated parent compounds. Contrary to recently published results (ref. 13), the difference in pKa between aliphatic aldehydes and ketones is indicated to be only ∼ 1 unit.