Enolization of acetone in superheated water detected via radical formation

Muoniated free radicals have been detected in muon-irradiated aqueous solutions of acetone at high temperatures and pressures. At temperatures below 250 degrees C, the radical product is consistent with muonium addition to the keto form of acetone. However, at higher temperatures, a different radical was detected, which is attributed to muonium addition to the enol form. Muon hyperfine coupling constants have been determined for both radicals over a wide range of temperatures, significantly extending the range of conditions under which these radicals and the keto-enol equilibrium have been studied.     

Enolization of the phosphoryl group

Enolization of the phosphoryl group has been studied where Y = PPh₃, CN, Ts, COOEt, CONEt₂; R and R′ = Et, Bu, Ph, EtO, BuO, PhO; and X = Cl, Br, ClO₄, BF₄. It has been established that substances with are phosphaenols, but in substances with Y = CONEt₂ the phosphoryl group cannot be enolized under any conditions. Phosphaenolization is favored by a high acidifying ability of the Y group, the ability of the X anion to stabilize the phosphaenolic form due to formation of a hydrogen bond OH…X with the anion, and a low electronegativity of R and R′ groups. To evaluate the acidifying ability of Y, this article defines specific σ⁻ constants dependent on the number of substituents at the α-carbon atom: σ_CH3⁻, σ_CH2⁻ and σ_CH⁻. Their sums characterize the enolization ability of the phosphoryl group. The enolic structure in the solid state is possible if ∑_CHn⁻ > 2. If this sum lies in the range of 2 < ∑_CHn⁻ < 2.6 the phosphoryl–phosphaenol tautomerism can be expected in appropriate solutions. Acidic properties of the investigated compounds in MeNO₂ and EtOH (absolute) have been determined. Calculations of the acidity of the phosphoryl CH forms (A) and of the phosphaenol OH forms (B) have been carried out.     

Enolization of the Phosphoryl Group

Abstract

The ability of the phosphoryl group to undergo enolization has been studied. The introduction of strongly electronegative substituents at thee α-carbon atom is shown to increase CH- acidity greately and result in the enolization of the P=O group.     

Boiling-induced changes in the mechanism of diglyme radiolysis

Boiling intensifies the radiolytic conversion of diglyme since it stimulates the cleavage of the C–O bonds in the excited molecules and the primary radical cations, enhances the radical exchange reactions, and weakens the diglyme regeneration reactions.

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Radical production in the radiolysis of liquid benzene

Iodine scavenging techniques have been used to examine the role of the phenyl radical in the radiolysis of benzene with γ-rays. Biphenyl, the main product in the radiolysis of neat benzene, and iodobenzene yields were determined as a function of iodine concentration. The yield of biphenyl in neat benzene is found to be 0.075 molecules/100 eV and independent of dose up to 1 Mrad. The addition of 0.1 mM iodine increases the biphenyl yield to about 0.4 molecules/100 eV. This increase is thought to be due to a reaction of iodine with the phenyl radical–benzene adduct, which apparently has a very long lifetime. Further addition of iodine leads to a decrease in biphenyl to about 0.09 molecules/100 eV at 30 mM iodine. This decrease is accompanied by an increase in iodobenzene from 0.04 to 0.32 molecules/100 eV. It appears that iodine can effectively compete with benzene for scavenging phenyl radicals.     

Track effects in the radiolysis of aromatic liquids

The chemical effects induced by the track structure of heavy ions have been exploited to show that H₂ production in the radiolysis of simple aromatic liquids (benzene, pyridine, toluene and aniline) is primarily due to second order processes. Similar dependences of H₂ yields on the linear energy transfer, LET, for each of these compounds suggest a common mechanism for H₂ formation. Furthermore, the yields of H₂ are significant at very high LET and they approach that found with aliphatic compounds. Yields of “dimers” (biphenyl, bibenzyl, dipyridyl, and diphenylamine for benzene, toluene, pyridine, and aniline, respectively) have different dependences on LET reflecting the variety of pathways leading to their production. Bibenzyl formation in toluene exhibits a complex dependence on LET suggesting several competing pathways for its production whereas biphenyl formation in benzene is nearly independent of LET suggesting a unimolecular process. Dipyridyl, and diphenylamine yields in pyridine and aniline, respectively, decrease with increasing LET, which indicates that their precursor is being depleted.     

Radical production in the radiolysis of liquid pyridine

A combined experimental and theoretical approach has been used to probe the radiolytic decomposition of liquid pyridine. The major single condensed phase product in the gamma-radiolysis of pyridine is dipyridyl with a yield of 1.25 molecules/100 eV total energy absorbed. Scavenging studies suggest that most, if not all, dipyridyl has a radical precursor, but only about 10% of that is due to the pyridyl radical. The remainder of the dipyridyl may be due to reaction of the parent radical cation with pyridine. Iodine scavenging and quantum chemical calculations both show that the ortho-pyridyl radical (2-pyridyl) is far more stable than the other two isomers.     

Radical yields in the radiolysis of cyclic compounds

The radiolytic decomposition of simple cyclic organic liquids mainly occurs by the breakage of a carbon–hydrogen bond giving the molecular radical and a hydrogen atom. Although the mechanism may be similar, very different yields are found for various six member rings such as cyclohexane, benzene, and pyridine. Experiments using iodine-scavenging techniques give both molecular radical and H atom yields directly and allow an examination of their correlation with each other in different condensed phase cyclic organics.     

Hydrogen production in the radiolysis of bromide solutions

The radiolysis of water without a protecting agent is found to form a low steady-state concentration of molecular hydrogen. The addition of bromide anion leads to a linear response for molecular hydrogen production with doses up to 300 kGy. Bromide concentrations are found to remain constant over this dose range due to recycling of the oxidized species containing the bromine atom by hydrated electrons, H atoms or HO₂ (O₂⁻). This process appears to occur many times with little change in total bromide anion concentration. Efficient electron scavengers are found to have no effect on bromide anion concentration except possibly at extremely high concentrations. Nitrous oxide saturated solutions show a significant depletion of bromide anion concentration with a concurrent formation of BrO₃⁻ and a suppressed yield of molecular hydrogen.     

如何解决Favorskii重排与酮多卤代反应机理中烯醇化的矛盾

酮的多元卤代和α-卤代酮的Favorskii重排都是醛酮教学的重要内容,且都是在碱性条件下烯醇化后发生的。但是,前者是在含有卤素一侧烯醇化,而后者却是在不含卤素一侧烯醇化。这种烯醇化的“随意性”常引起学生困惑,甚至认为此2处的烯醇化是“矛盾”的。通过分析卤代酮烯醇化的可逆性和Favorskii重排的不可逆性合理地解释了Favorskii重排中烯醇化的合理性,化解了教学中的这一“矛盾”。     

Gamma radiolysis of morin

Gamma irradiation studies of morin (10^–5M) in ethanol and dimethyl sulphoxide (DMSO) in the dose range of 149–895 Gy and of 4.5–45 Gy were carried out, respectively, in aerated and anoxic conditions purged with nitrogen and nitrous oxide. The decoloration yield of morin was studied as a function of dose. The relative radiation sensitivity was estimated under similar conditions. The effect of the concentration (10^–5–10^–4M) of iodine, succinic acid and acryl amide on radiolysis of morin was investigated at constant dose in both solvents and results were interpreted in terms of scavenging reactions.     

Proton pulse radiolysis

A 5 Me V proton accelerator has been used for pulse radiolysis of organic gases. The transient spectra obtained from the alkanes methane, ethane, propane, n-butane and neopentane have tentatively been assigned to alkyl radicals. Some methodological aspects of this new technique are discussed.     

Structure of the intermediate particles in the radiolysis of indolinespiropyran

Calculations by the extended Hückel iteration method with self-consistency with respect to the charges were undertaken for the initial molecule, the radicalanion, and the neutral radical formed during protonation of the latter in 1,3,3-trimethylspiro[indoline-2,2-(2H)-chromene]. On the basis of the results from the calculations and analysis of the ESR spectrum of the neutral radical it was concluded that the bond between the spiro carbon atom and the oxygen heteroatom of the pyran ring is not broken during the formation of the radical-anion and its subsequent protonation and that the unpaired electron is delocalized in the system of the benzopyran fragment of the molecule. Protonation in the radicalanion takes place at the carbon atom at position 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1620–1623, December, 1986.     

Surface species produced in the radiolysis of zirconia nanoparticles

Modifications to water-zirconia nanoparticle interfaces induced by gamma irradiation have been examined using diffuse reflection infrared Fourier transform (DRIFT), Raman scattering, and electron paramagnetic resonance (EPR) techniques. Spectroscopy with in situ heating was used to probe variations in the dissociatively bound chemisorbed water on the zirconia nanoparticles following evaporation of the physisorbed water. DRIFT spectra show that the bridged Zr-OH-Zr species decreases relative to the terminal Zr-OH species upon irradiation. No variation is observed with Raman scattering, indicating that the zirconia morphology is unchanged. EPR measurements suggest the possible formation of the superoxide ion, presumably by modification of the surface OH groups. Trapped electrons and interstitial H atoms are also observed by EPR.