Thermal decomposition reaction of 3,3,6,6-tetramethyl- 1,2,4,5-tetroxane in 2-methoxy- ethanol solution

The thermal decomposition study of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (acetone cyclic diperoxide) was carried out in 2-methoxyethanol solution in the 130-166 °C temperature range. The overall reaction follows a first-order kinetic law up to at least 75% diperoxide conversion. The activation parameters (ΔH^# = 22.5 ± 0.7 kcal⋅mol^–1 and ΔS^# = -25.6 ± 0.5 cal⋅mol^–1⋅K^–1) for the unimolecular rupture of the O–O bond in the diperoxide molecule were obtained by measuring the remnant diperoxide at different reaction times by the CG technique. Acetone was detected by GC as the major organic product of the reaction.     

Catalytic effect of cuprous ions on the thermal decomposition of 3,3,6,6-tetramethyl-1,2,4,5-tetraoxane in methanol solution

Thermal decomposition of 3,3,6,6-tetramethyl-1,2,4,5-tetraoxane was examined in methanol solution (1.69×10⁻² M) containing cuprous ions (5.05×10⁻⁷ M) in the temperature range from 130 to 166°C using UV spectroscopy as analytical method. The ion-catalyzed reaction follows first-order kinetics with respect to the peroxide and added cuprous ions. The temperature effect on the rate of thermal decomposition of the title compound was described by the corresponding Arrhenius equations, and its stability in solution was estimated on a quantitative level. The activation parameters of the initial step of decomposition of 3,3,6,6-tetramethyl-1,2,4,5-tetraoxane were determined (ΔH ^≠ = 14.7±0.8 kcal mol⁻¹; ΔS ^≠ = −38.9±1.4 cal mol⁻¹ K⁻¹; ΔG ^≠ = 31.0±0.8 kcal mol⁻¹). Electron-transfer mechanism was proposed for the reaction under study. The text was submitted by the authors in English.     

Spectroscopic study of the dispiro-1,2,4,5-tetroxane (cyclohexanone diperoxide)

The aim of this work is to present results derived from experimental IR and UV spectra and theoretical studies of DPCH, in order to get a more deeper insight on the physicochemical properties of this compound to gain a more deep knowledge of its action, helping in the design of new compounds with antimalaric effects. Experimental results are analyzed on the basis of theoretical calculations, which allow to derive suitable interpretations of spectral data.     

Experimental preparation and UV/IR spectroscopic characterization of 1,3-dibutanal-1,2,4,5-tetroxane

We report the experimental preparation of the 1,3-butanal-1,2,4,5-tetroxane by oxidation of glutataldehyde with oxygen peroxide in presence of concentrated sulfuric acid, following the Bayer and Viller method modified by Jorge et al. The UV and IR spectra are studied from the experimental and theoretical standpoint. A rather complete vibrational assignment was performed and the nature of the electronic transitions was discussed in detail.     

3,3,6,6‐Tetra­methyl‐1,2,4,5‐tetroxane: a twinned crystal structure

The title compound, C₆H₁₂O₄, also known as dimeric acetone peroxide, Me₂(C₂O₄)Me₂, has crystallographically imposed inversion symmetry and adopts a chair conformation in the solid state. This structure contrasts with that of the sulfur homologue Me₂(C₂S₄)Me₂, which has crystallographically imposed symmetry and crystallizes in a twist‐boat conformation. Crystals of the title compound are twinned along the reciprocal c* axis.     

Gas-phase structure and conformational properties of copper (I) pivalate dimer (CuC5H9O2)2

The molecular structure and conformational properties of gaseous dimer of copper (I) pivalate, Cu₂piv₂, have been studied by gas electron diffraction (GED) at 413(5) K and quantum chemical calculations (DFT and MP2). The molecule possesses a planar eight-membered skeleton. Two conformers, “staggered” of C _2h symmetry and “eclipsed” of C _2v symmetry, were found for Cu₂piv₂ in the gas phase. The following geometric parameters of the skeleton ring and the tert-butyl groups have been determined from the GED experiment for the “staggered” form: r_g(Cu···Cu) = 2.520(8) Å, r_g(Cu–O)_ave = 1.871(4) Å, r_g(C–O)_ave = 1.273(3) Å, r_g(C–C)_ring-tert = 1.531(4) Å, r_g(C–C)_{tert-out-of-plane-ring} = 1.536(4) Å, r_g(C–C)_{tert-in-the-plane-ring} = 1.527(4) Å, r_g(C–H)_ave = 1.087(5) Å, (O–Cu–O) = 172.12°(3). Computations predict the internal rotation of the tert-butyl groups to be independent. The value of calculated Wiberg bond index for Cu···Cu testifies the existence of weak bonding between two copper atoms.

     

Transformation of 9-Aryl-3,3,6,6-tetramethyl-1,2,3,4,5,6,7,8,9,10- decahydroacridine-1,8-diones in Mineral Acids

Russian Journal of Organic Chemistry -     

Preparation,molecular-crystal structure,and chemical peculiarities of the potassium salt of 3,3,6,6-tetramethyl-1,8-dioxo-1,2, 3,4,5,6,7,8,9,10-decahydroacridine-9-carboxylic acid

It was established by x-ray diffraction analysis that the crystalline title compound exists as a dimer formed by two paired potassium ions bonded to the oxygen atoms of the carboxy group and the coordinated oxygen atoms of the carbonyl groups. The solvate of the dimer with the composition 2C₁₈H₂₂NO₄K·3H₂O·CH₃COCH₃ is the crystallochemically independent structural unit. A shift of the electron density toward the carbonyl groups and the formation of a strong hydrogen bond between NH and the oxygen atom of the carboxylate group are observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 666–672, May, 1980.     

A dynamic nuclear magnetic resonance spectroscopic study of conformational properties of 1,3-dioxepane and 4,4,7,7-tetramethyl-1,3-dioxepane

The 251 MHz ¹H and the natural abundance 63.1 MHz ¹³C NMR spectra of 1,3-dioxepane (1) and 4,4,7,7-tetramethyl-1,3-dioxepane (2) have been investigated over the temperature range of 5 to ?180 °C. While the spectra of 1 show no dynamic NMR effect, compound 2 exists in solution as a 1:1 mixture of a symmetrical (C₂) twist-chair and its mirror image conformation. The free energy barrier for the conformational racemization of 2 is 43 kJ mol^?1 (10.3 kcal mol^?1). Interconversion paths between various conformations of 2 are discussed. Compound 1 is suggested to have a symmetrical (C₂) twist-chair conformation which is rapidly pseudorotating via a chair conformation to achieve a time averaged symmetry of C_2v, even at ?180 °C.     

Electronic structure and conformational properties of (carboxy-alkenyl)-phosphonic acids

The general conformational properties and electronic structure of (carboxy-alkenyl)-phosphonic derivatives were determined at RHF/STO-3G^* level. In all the series, low rotation barriers were found for the two C=C/P=O conformers. In the compounds in which the interactions between the carboxylic and phosphonic moieties are smaller, the most stable conformers are the C=C/P=O s-cis ones. In most of the conformers, the C=C/C=O system presents the disposition s-cis. The Z-(2-carboxy-vinyl) and Z-(2-carboxy-propenyl) phosphonic acids present intramolecular hydrogen bonds, existing in at least four conformer with internal hydrogen bonds. These last compounds were more rigorously studied at RHF/3-21G^* and RHF/6-31G^** levels. The most stable conformer shows a trans structure for the C=C/P=O angle, with an intramolecular hydrogen bond located between the hydroxylic hydrogen of phosphonic group and the carbonyl oxygen of carboxylic moiety. A secondary conformer is found with a double intramolecular hydrogen bond between two hydroxylic hydrogens of the phosphonic moiety and the oxygen of carboxylic bond. Another secondary conformer appears with an intramolecular hydrogen bond between the oxygen of the phosphoryl bond and the hydroxylic hydrogen of the carboxylic group. A study of the topology of charge densities is carried out. This analysis reveals bonds with an ionic participation. A very weak π conjugation, variable with the conformers, is found in the C=C/P=O system, as well as a strongly polarized P=O partial triple bond. The intramolecular hydrogen bonds give rise to cyclic structures.     

Gas-phase thermochemical properties of pyrimidine nucleobases

The gas-phase acidity and proton affinity of thymine, cytosine, and 1-methyl cytosine have been examined using both theoretical (B3LYP/6-31+G*) and experimental (bracketing, Cooks kinetic) methods. This paper represents a comprehensive examination of multiple acidic sites of thymine and cytosine and of the acidity and proton affinity of thymine, cytosine, and 1-methyl cytosine. Thymine exists as the most stable "canonical" tautomer in the gas phase, with a DeltaH(acid) of 335 +/- 4 kcal mol(-1) (DeltaG(acid) = 328 +/- 4 kcal mol(-1)) for the more acidic N1-H. The acidity of the less acidic N3-H site has not, heretofore, been measured; we bracket a DeltaH(acid) value of 346 +/- 3 kcal mol(-1) (DeltaG(acid) = 339 +/- 3 kcal mol(-1)). The proton affinity (PA = DeltaH) of thymine is measured to be 211 +/- 3 kcal mol(-1) (GB = DeltaG = 203 +/- 3 kcal mol(-1)). Cytosine is known to have several stable tautomers in the gas phase in contrast to in solution, where the canonical tautomer predominates. Using bracketing methods in an FTMS, we measure a DeltaH(acid) for the more acidic site of 342 +/- 3 kcal mol(-1) (DeltaG(acid) = 335 +/- 3 kcal mol(-1)). The DeltaH(acid) of the less acidic site, previously unknown, is 352 +/- 4 kcal mol(-1) (345 +/- 4 kcal mol(-1)). The proton affinity is 228 +/- 3 kcal mol(-1) (GB = 220 +/- 3 kcal mol(-1)). Comparison of these values to calculations indicates that we most likely have a mixture of the canonical tautomer and two enol tautomers and possibly an imine tautomer under our conditions in the gas phase. We also measure the acidity and proton affinity of cytosine using the extended Cooks kinetic method. We form the proton-bound dimers via electrospray of an aqueous solution, which favors cytosine in the canonical form. The acidity of cytosine using this method is DeltaH(acid) = 343 +/- 3 kcal mol(-1), PA = 227 +/- 3 kcal mol(-1). We also examined 1-methyl cytosine, which has fewer accessible tautomers than cytosine. We measure a DeltaH(acid) of 349 +/- 3 kcal mol(-1) (DeltaG(acid) = 342 +/- 3 kcal mol(-1)) and a PA of 230 +/- 3 kcal mol(-1) (GB = 223 +/- 3 kcal mol(-1)). Our ultimate goal is to understand the intrinsic reactivity of nucleobases; gas-phase acidic and basic properties are of interest for chemical reasons and also possibly for biological purposes because biological media can be quite nonpolar.     

Gas-phase structures, rotational barriers, and conformational properties of hydroxyl and mercapto derivatives of cyclohexa-2,5-dienone and cyclohexa-2,5-dienthione

The rotational barriers and conformational properties of the hydroxyl and mercapto groups attached to the alpha and beta positions of cyclohexa-2,5-dione and cyclohexa-2,5-dienthione have been studied at the B3LYP/ 6-311++G(d,p) level of theory. The results show that the conformational preferences of these studied systems are the result of a subtle interplay between different competing effects (conjugation, hyperconjugation, and steric repulsions). The applicability of the density functional theory reactivity indices and the maximum hardness principle for the present systems has been analyzed.     

Gas-phase acid-base properties of melamine and cyanuric acid

The thermochemical properties of melamine and cyanuric acid were characterized using mass spectrometry measurements along with computational studies. A triple-quadrupole mass spectrometer was employed with the application of the extended Cooks kinetic method. The proton affinity (PA), gas-phase basicity (GB), and protonation entropy (Δ_pS) of melamine were determined to be 226.2 ± 2.0 kcal/mol, 218.4 ± 2.0 kcal/mol, and 26.2 ± 2.0 cal/mol K, respectively. The deprotonation enthalpy (Δ_acidH), gas-phase acidity (Δ_acidG), and deprotonation entropy (Δ_acidS) of cyanuric acid were determined to be 330.7 ± 2.0 kcal/mol, 322.9 ± 2.0 kcal/mol, and 26.1 ± 2.0 cal/mol K, respectively. The geometries and energetics of melamine, cyanuric acid, and related ionic species were calculated at the B3LYP/6-31+G(d) level of theory. The computationally predicted proton affinity of melamine (225.9 kcal/mol) and gas-phase deprotonation enthalpy of cyanuric acid (328.4 kcal/mol) agree well with the experimental results. Melamine is best represented as the imide-like triazine-triamine form and the triazine nitrogen is more basic than the amino group nitrogen. Cyanuric acid is best represented as the keto-like tautomer and the N-H group is the most probable proton donor.     

Gas-phase structure of N,N-dimethylglycine.

Three conformers of the neutral amino acid N,N-dimethylglycine [(CH3)2NCH2COOH] were detected in a supersonic expansion by a combination of laser ablation (LA) and molecular-beam Fourier transform microwave (MB-FTMW) spectroscopy. A bifurcated methyl-to-carbonyl (C--HO==C) weak intramolecular hydrogen bond might stabilise the most stable conformer of C(s) symmetry. The second most stable conformer of C1 symmetry has a hydrogen bond between the hydroxyl group and the lone pair at the nitrogen atom (NH--O). The r(s) and r0 structures were derived for this conformer from the rotational data for the parent and six minor 13C, 15N and OD isotopomers. A third conformer exhibits a cis-carboxyl functional group and C1 symmetry. Ab initio MP2/6-311++G(d,p) predictions of the spectroscopic parameters were useful in analysing the spectra. In particular, the agreement of the nuclear quadrupole coupling constants with those calculated was conclusive in identifying the different conformers.