Oxygen Bond Formation Research Articles

A Density Functional Study of the Addition of Water to SO3 in the Gas Phase and in Aqueous Solution

The addition of water to sulfur trioxide in liquid water has been studied using the ab initio molecular dynamics (MD) method. The hydration reaction observed in the MD simulation is spontaneous and, within a few hundred femtoseconds, yields a contact ion pair consisting of a hydrogen sulfate anion and a hydronium cation. The reaction mechanism is concerted: sulfur−oxygen bond formation and deprotonation of the hydrating water occur simultaneously. The reaction in solution is compared to two gas-phase additions, namely, the bare reaction with only the two reactants present and the reaction catalyzed by an additional water molecule. Both of these reactions lead to neutral products and require substantial amounts of activation energy. The gas-phase results have also been used to evaluate the accuracy of the BLYP (Becke−Lee−Yang−Parr) functional, which has been used in the ab initio MD to determine the density functional electronic structure. Whereas the calculated geometries of the sulfur trioxide−water com...

Mechanism of One-Electron Oxidation of β-, γ-, and δ-Hydroxyalkyl Sulfides. Catalysis through Intramolecular Proton Transfer and Sulfur−Oxygen Bond Formation

The mechanism of photoinduced electron transfer between sulfur-containing alcohols and the 4-carboxybenzophenone (CB) triplet state in aqueous solution was investigated using laser flash photolysis and steady-state photolysis techniques. Bimolecular rate constants for quenching of the CB triplet state by five hydroxyalkyl sulfides, 2-(methylthio)ethanol (2-MTE), 2,2‘-dihydroxydiethyl sulfide (2,2‘-DHE), 3-(methylthio)propanol (3-MTP), 3,3‘-dihydroxydipropyl sulfide (3,3‘-DHP), and 4-(methylthio)butanol (4-MTB), with varying numbers of OH groups and varying locations with respect to the sulfur atom, were determined to be in the range (3.3−4.8) × 109 M-1 s-1 for neutral solutions. The intermediates identified were the CB ketyl radical anion (CB•-), the CB ketyl radical (CBH•), and intermolecularly (S∴S)-bonded radical cations. An additional absorption band at approximately 400 nm in the transient spectra for some of the hydroxyalkyl sulfides was assigned to the intramolecularly (•S−O)-bonded species (only f...

Phosphorus–oxygen bond formation on organo-capped tricobalt centres via phosphorus–hydrogen or phosphorus–phosphorus bond scission

Chromatographic work-up of the initial products of the reaction of the secondary phosphine PPh2H with [Co3(µ3-CR)(CO)9] (R = Me 1a or CO2Me 1b) at 308 K in heptane gave the mono- and bis-substituted complexes [Co3(µ3-CR)(CO)8(PPh2H)] (R = Me 2a or CO2Me 2b) and [Co3(µ3-CR)(CO)7(PPh2H)2] (R Me 3a or CO2Me 3b) and, in addition, when R = Me, the complex [Co3(µ3-CMe)(µ-Ph2POPPh2)(CO)6(PPh2H)] 4a, in which phosphorus–oxygen bond formation has occurred. Thermolysis of complex 2a at 343 K in heptane gave 1a and [Co3(µ3-CMe)(µ-H)(µ-PPh2)(CO)7] 5a, while thermolysis of 3a under the same conditions afforded 4a, a trace of 5a and [Co3(µ3-CMe)(µ-H)(µ-PPh2)(CO)6(PPh2H)] 6a. Similar reactions with the µ3-CCO2Me capped species 2b and 3b resulted in unstable non-isolable species. Treatment of complexes 3a, 3b with CO at 343 K causes the replacement of first one and then the other PPh2H ligand by CO to give 2a, 2b and then 1a, 1b respectively, while reformation of a phosphorus–hydrogen bond to give initially 2a or 3a can be achieved on carbonylation of either complex 5a or 6a. Substitution of a PPh2H group in 4a can be achieved by purging with CO to give [Co3(µ3-CMe)(µ-Ph2POPPh2)(CO)7] 7a. Complex 7a can also be prepared directly by the reaction of 1a with the diphosphane P2Ph4 as can the analogue [Co3(µ3-CCO2Me)(µ-Ph2POPPh2)(CO)7] 7b on reaction of 1b. The intermediates [Co3(µ3-CR)(CO)8(P2Ph4)] (R = Me 8a or CO2Me 8b) and [Co3(µ3-CR)(µ-P2Ph4)(CO)7] (R = Me 9a or CO2Me 9b) isolated in the reactions can be converted under the same reaction conditions into 7a and 7b respectively. Complex [Co3(µ3-CMe)(µ-Ph2POPPh2)(CO)6(PPhMe2)] 4a′, the tertiary phosphine analogue of 4a, has been prepared from the reaction of 7a with PPhMe2. The structures of complexes 4a′ and 5a have been determined by single crystal X-ray diffraction studies.

Semiempirical and ab initio transition state calculations for the transformation of N-acetyltetrazoles into corresponding 1,3,4-oxadiazoles

The transformation of 2-acetyl-5-substituted-tetrazoles into the corresponding 1,3,4-oxadiazoles was studied with the mopac semiempirical and gaussian ab initio methods. Two mechanisms, one with two transition states and the other with three, were elucidated by mopac. The first mechanism supported by PM3 and MNDO has a two-step, almost concerted, mechanism for the elimination of a nitrogen molecule from the tetrazole ring and formation of the oxadiazole product from an open-chain intermediate through carbon C 5 and acetyl oxygen bond formation. The second mechanism supported by AM1 and MINDO/3 breaks the elimination of the nitrogen molecule into two steps: first breaking the N 4-C 5 and then the N 2-N 3 bonds. Even when the AM1 and MINDO/3 transition state structures were optimized by PM3 and MNDO, the obtained transition states present only one bond breaking. The HF/STO-3G and HF/3-21G ab initio methods agree with the first mechanism where two bonds are breaking almost simultaneously. Despite the disagreement in the mechanism of the nitrogen elimination, the transition state that presents the product formation from open-chain intermediates is quite similar for all methods studied. The semiempirical calculation of this transition state is possible only if it is assumed that it has biradical character. The activation energies calculated by PM3 seem to be insensitive to the nature of the substituents.

Secondary α‐deuterium isotpe effect on the hydration of p‐nitrobenzaldehyde

AbstractThe secondary α‐deuterium isotpe effect on the equiliburium constant (KD/KH) for the hydration of p‐nitrobenzaldehyde is 1·39 ± 0·05. The Kinetic secondary α‐deuterium isotope effect (KD/KH) for the addition of water to p‐nitrobenzaldehyde is 1·18 ± 0·07. This result demonstrates that there is extensive carbon–oxygen bond formation in the transition state for addition of water to the carbonyl group of p‐nitrobezaldehyde.

Photoemission study of oxygen adsorption on ternary silicides

Molecular oxygen adsorption on several ternary silicides (Ti4M4Si7, M=Ni,Co) and (TiFeSi2) is studied using photoemission. The valence band spectrum shows that the O2 dissociates on adsorption and suggests that an exposure of a few hundred langmuirs is sufficient to completely cover the surface with a layer of atomic oxygen. Si 2p core‐level spectra show that oxygen bonds with the silicon and photoemission peaks from all oxidation states of silicon are observed. 3p core levels from the metallic elements like titanium do not show core‐level components indicating the formation of metal–oxygen bonds. The bonding of oxygen to silicon could be due to silicon termination of the surface or maybe due to energetics which favor silicon–oxygen bond formation over metal–oxygen bond formation, the breaking of silicon–silicon bonds rather than silicon–metal bonds or the breaking of the fewest atomic bonds.

Electro-organic reactions part 35. Efficient carbon—oxygen bond formation in the anodic coupling of pyridopyrimidine derivatives.

4-H-Pyrido[1,2-a]pyrimidine-2,4-diones (Chichibabin) derivatives, formed by condensation of 2-aminopyridines with substituted dialkylmalonates, are electroactive. In solution in CH 2Cl 2/CF 3CO 2H mixtures they are smoothly and selectively anodically coupled in high yield. The products are novel and unexpected; radical coupling at the C-3 and O-4 positions is involved and the proposed mechanism is analogous to that of oxidative phenolic coupling.

Isobutane chemical ionization mass spectra of unsaturated alcohols

AbstractAnalysis of the isobutane chemical ionization mass spectra of hexenols, cyclohexenols and various syn/anti pairs of bicyclic and tricyclic homoallylic alcohols shows that: (i) the spectra of the allylic alcohols are dominated by [M + H – H2O]+ and [M + C4H9–H2O]+ ions and contain traces of [M + H]+ ions; (ii) [M + H]+ ions are prominent in the spectra of acyclic and certain cyclic homoallylic alcohols; and (iii) [M + H]+ ions dominate the spectra of other acyclic unsaturated alcohols. The [M + H]+ ions may result from either: (a) protonation of the hydroxyl group, followed by a very rapid intramolecular proton transfer from the protonated hydroxyl group to the carbon–carbon double bond or internal solvation of the protonated hydroxyl group by the carbon–carbon double bond; and/or (b) direct protonation of the carbon–carbon double bond with significant internal solvation of the resulting carbocation by the hydroxyl group, which may lead to carbon–oxygen bond formation to give a protonated cyclic ether. The consequences of placing various geometric constraints on the possible intramolecular interactions between the hydroxyl group and the carbon–carbon double bond in unsaturated alcohols are explored.

Muon-oxygen bonding in V2O3

A muon site search using calculated internal fields has been performed for V2O3, where purely dipolar fields allow a site determination free from covalent complications. The obtained sites are a subset of the Rodriguez and Bates sites found in α-Fe2O3 and indicate muon oxygen bond formation. The sites missing at low temperatures are consistent with the vanadium pairing mechanism for the metal-to-insulator (corundum-to-monoclinic) phase transition.

Oxidation of transition-metal cations in the gas phase. Oxygen bond dissociation energies and formation of an excited-state product

Oxidation of transition-metal cations in the gas phase. Oxygen bond dissociation energies and formation of an excited-state product

Secondary deuterium isotope effects for certain acyl transfer reactions of phenyl formates

Kinetic ..cap alpha.. secondary deuterium isotope effects, k/sub D//k/sub H/, for formyl group transfer from either the 4-methoxyphenyl or 4-nitrophenyl esters, or both, of formic and deuterioformic acids to a variety of oxygen acceptors have been measured at 25/sup 0/C in aqueous solution: hydroperoxide ion, 1.12; 2-propynol anion, 1.13; hexafluoropropan-2-ol anion, 1.14; and water, 1.22. In addition, corresponding isotope effects have been obtained for general-base-catalyzed formyl group transfer from the same substrates to acetate, 1.21, formate, 1.23, and trimethylamine N-oxide, 1.20. The ..cap alpha.. secondary deuterium isotope effect for acid-catalyzed hydrolysis of both esters has been determined to be 1.24. These data are interpreted to reflect considerable, and perhaps complete, carbon--oxygen bond formation in the transition state for addition of oxygen nucleophiles to phenyl formates. Finally, corresponding isotope effects were determined for reaction of fluoride, 1.19, and azide, 1.14, which also suggest substantial covalent bond formation between ester and nucleophile in the transition state. 4 tables.

A sensitive analytical method for pyrrolizidine alkaloids. The mass spectra of retronecine derivatives.

The pyrrolizidine alkaloids in Senecio jacobaea can be hydrolyzed to the common base, retronecine, and derivatized to form the bistrifluoroacetate, bisheptafluorobutyrate, diacetate and bistrimethylsilyl ether. The analysis of the fluorinated compounds by electron capture provides sensitivity for detection of these alkaloids. The bond weakening effect in the ion formed on electron impact, between the allylic carbon and alkyl ester oxygen due to the electron withdrawing fluorinated groups of the ester, changes the driving force for fragmentation from the nitrogen alpha-cleavage reaction to a charge site migration. This yields alkyl-oxygen bond cleavage and formation of a stabilized allylic cation which is the base peak.

Electron spectroscopic study of oxygen-plasma-treated polymer surfaces

Oxygen plasma treatment of ABS polymer surfaces has the effect of increasing the adhesion of evaporated metal films on those surfaces. To help understand this, surfaces of commercial ABS and polypropylene were examined with ESCA both before and after oxygen plasma treatment. The plasma treatment was found to change the basic chemical nature of the polymer surface by increasing the number of single and double bonds between carbon and oxygen atoms. It is suspected that these additional carbon–oxygen chemical bonds affect the adhesion between polymers and metals. In addition to the carbon–oxygen bond formation, the plasma treatment removed residual impurities of silicon and increased the residual amounts of other metallic impurities originating in the bulk. The binding energies of these metallic impurities are all indicative of oxides.

The photochemical ring expansion of cyclic ketones

The photochemical conversion of cyclic ketones in alcoholic solution to ring-expanded cyclic acetals was first observed in the cases of cyclocamphanone and nortricyclanone. This reaction has subsequently been shown to be general for cyclobutanones. It has not been observed for simple cyclopentanones, but occurs with some, but not all, bicyclo [2.2.1]-heptan-2-ones and with cyclopentanones having a α-cyclopropyl ring. It has not been observed for any carbocyclic ketone with a six-membered or larger ring. The reaction is considered to proceed via a cyclic oxacarbene, which is formed in the case of five-membered cyclic ketones by α-cleavage followed by carbon—oxygen bond formation in the resulting alkyl acyl biradical. It is proposed that the ring expansion of cyclic ketones to cyclic acetals is dependent upon structural features that either facilitate oxacarbene formation, e.g., an α-cyclopropyl ring, and/or inhibit competing reactions, e.g., enal formation.

The mechanism of the thermal rearrangement of β-ketosilanes

The rates of thermal rearrangement of a series of 1-(aryldimethylsilyl)-2-propanones have been determined at 150°, 160° and 170°. The reaction is first order in all cases, with energies of activation ranging from 30.6 to 32.9 kcal/mol. A Hammettt plot of log k vs σ p gives a p value of + 0.54, indicating only slight silicon—oxygen bond formation before silicon—carbon bond breaking.

The mechanism of the β-ketosilane to siloxyalkene thermal rearrangement

The mechanism of the β-ketosilane to siloxyalkene rearrangement has been investigated. The reaction followed first order kinetics for a wide variety of compounds. Activation parameters have been determined for six compounds. For a series of p-substituted triphenylsilylacetophenones log k vs. σ p gave a Hammett p value of −0.78. The data are consistent with an intramolecular concerted rearrangement involving a four-centre transition state where silicon—oxygen bond formation cannot significantly precede silicon—carbon bond breaking. Molecular orbital calculations were consistent with this view.

Alkyl–oxygen bond formation in the mass spectra of α‐chloromethyl aryl sulphones

AbstractWhen subjected to electron‐impact, chloromethyl aryl sulphones (II, X = Cl) fragment predominantly by the loss of CH2Cl from the molecular ion followed by the loss of SO2 and in most cases the appropriate metastable peaks are present to confirm the transitions. In addition, alkyl–oxygen bond formation in the molecular ion was revealed by the presence of prominent peaks corresponding to the [Rϕ‐SO]+ ions. In most spectra no evidence for aryl–oxygen bond formation could be found and thus the presence of the chlorine atom was able to effectively reverse the direction of skeletal rearrangement reported for aryl methyl sulphones.

Réactions des céténes et du dicéténe avec les germyl- et silylphosphines

Ketenes add to germyl- and silylphosphines R 3MPEt 2 with opening of the carbonyl group and formation of phosphorylated alkenoxygermanes or -silanes ▪ (R′H, Ph). These adducts are thermally stable and only the addition derivative of diphenylketene and Me 3SiPEt 2 exhibits metallotropic isomerization to a C-derivative after prolonged heating. Hydrolysis of these addition compounds is a new approach to the acylphosphines R 2CH-CO-PEt 2. Diketene also reacts with germyl- and silylphosphines with acyloxygen bond cleavage and formation of metallated and phosphorylated ketoenolates of the type ▪. These derivatives isomerize either partially (MSi) or completely (MGe) into R 3MOC(CH 3)CHCOPEt 2. Their hydrolysis constitutes a new method of synthesis of the phosphorylated β-diketone ▪. The ketoenolates from the addition reaction of the hydrosilylphosphine, Me 2Si(H)PEt 2, cyclize readily after partial isomerization by the intramolecular addition SiH to CO, to give phosphorylated siladioxane and siladioxene. The conformation of these heterocyclic compounds has been studied.

Base-catalysed cleavage of allylic derivatives of group EVA elements II. Reactions of cinnamyl and benzyl derivatives in strongly basic media

The rates of cleavage of cinnamyl and benzyl derivatives of silicon, germanium and tin in strongly basic media have been measured spectrophotometrically. Correlations between these rates and acidity functions H −, J − and H R− were made and kinetic solvent isotope effects evaluated. For the cinnamyl derivatives, the yield of allylbenzene (S' E product) was much greater in aqueous alcohol than in aqueous DMSO. It was concluded that the transition states for the cleavages in DMSO solvent mixtures had much more carbanion character than those in aqueous alcohol. The tin transition states appeared to involve a greater degree of tinoxygen bond formation than those of the silanes, where some evidence for an assisted pathway is presented. In the tin series, the transition state for the benzyl derivative has a greater ionic character than that of the cinnamyl analogue. There appears little evidence for any nucleophilic assistance in the latter case.

Synthesis of 1,6-dioxa-6a-thiapentalenes: sulphur–oxygen coupling by thallium(III) trifluoroacetate

4H-Pyran-4-thiones react with thallium(III) trifluoroacetate to form thallium-containing pyrylium trifluoroacetates which are ring-opened by water; the resulting intermediates spontaneously lose thallium(I) trifluoroacetate, with concomitant sulphur–oxygen bond formation, to give 1,6-dioxa-6a-thiapentalenes.