Molecular mechanics of peroxides. I. Parametrization and conformational analysis of linear compounds

A force field has been developed for use in MM2 calculations of geometric and energy data for linear peroxides R₁? O? O? R₂ and tested in some of them (R₁, R₂ = H, Me, Et, Prⁱ, Bu^t). The field obtained yield results that agree considerably better with experimental and ab initio data than those afforded by the only set of estimated parameters hitherto available.     

Aluminoxanes with acetylacetonate substituents

The reaction of tetraalkylaluminoxanes (R₄Al₂O; R  Me, Et and i-Bu) with acetylacetone (acacH) has been studied at various molar ratios. The acetylacetonate substituents were found to have a destabilizing effect on the stability of the aluminoxanes. The stability of these compounds decreases in the order: R₄Al₂O > R₃acacAl₂O > R₂(acac)₂Al₂O ? (acac)₄Al₂O.Aluminoxanes with acetylacetonate substituents undergo disproportionation, yielding aluminium trisacetylacetonate. The alkyl group also has an effect on the stability of alkylacetylacetonatoaluminoxanes, which decreases in the order i-Bu > Et > Me.     

Free radical abstraction of H atom from peroxides with concerted dissociation of O-O bond

Quantum chemical calculations of the dissociation energy of the C-H bond in the ??-hydroperoxide fragment of Me₂CHOOH were carried out. It was shown that abstraction of H atom is accompanied by dissociation of the O-O bond. Density functional calculations of transition states of the reactions of ^·CH₃, CH₃OO^·, and HO₂ ^· radicals with the C-H bond in the ??-hydroperoxide fragment of Me₂CHOOH were carried out. It was established that H atom abstraction is accompanied by concerted dissociation of the O-O bond. For 45 peroxides R¹R²CHOOH, R¹R²CHOOR³, and R¹R²CHOOC(O)R³ (R¹, R² = H, Me, Et, Ph, H₂C=CH), the enthalpies of H atom abstraction from the C-H bond in the a-hydroperoxide fragment with fragmentation of the peroxides at the O-O bond were calculated. The kinetic parameters for 12 classes of radical abstraction reactions with fragmentation of molecules were calculated from experimental data within the framework of the model of intersecting parabolas. The activation energies and reaction rate constants of H atom abstraction from C-H bonds of a-peroxide fragments involving peroxyl and alkyl radicals were determined for 45 peroxides of different structure.     

Verfeinerung der Kristallstruktur von K2O2

Refinement of the Crystal Structure of K₂O₂ The crystal structure of K₂O₂ has been refined using 241 diffractometer data (Cmca; a = 6.733(1), b = 6.996(1), c = 6.474(1) Å; Z = 4; R_w = 0.050). The distance O? O (1.541(6) Å) is significantly larger than that one assumed for alkali metal peroxides, so far.     

Structure and conformation in molecular peroxides

Molecular structures and energies have been calculated in the MINDO approximation for fifteen neutral and anionic peroxides: fully optimized torsional potential functions have been calculated for twelve of these, and torsional potential functions, subject to constrained optimizations, for a further two peroxides. Bond dissociation energies D(R₁O—OR₂) were also calculated. Equilibrium structures and energies were calculated for the polyoxo species H₂O_n, HO_nF, F₂O_n, HO_n and FO_n (n ? 4), and a complete set of bond dissociation energies derived for H₂O_n, HO_nF, and F₂O_n.     

Selective mixed coupling of carboxylic acids (I). - Electrolysis,thermolysis and photolysis of unsymmetrical diacyl peroxides with acyclic and cyclic alkyl groups

14 Unsymmetrical diacyl peroxides (R¹CO₂-O₂CR₂ with R¹: undecyl; R²: e.g. methyl, propyl, pentyl, nonyl, 2-methylpropyl, 2-propyl, 2-pentyl, cyclopropyl, cyclobutyl, cyclohexyl) are prepared in 85 to 92 % yield. Square pulse electrolysis of dodecanoyl octanoyl peroxide ($\text{li}$) affords the unsymmetrical coupling product octadecane($\text{4}$)ins poor yield and selectivity. Thermolysis or photolysis in solution produces preferentially $\text{4}$, but also considerable amounts of disproportionation products. At ?78°C the neat peroxides are photolysed selectively to the mixed dimers. With straight chain and β-branched alkyl groups high yields are obtained (63 – 76 %), with cycloalkyl groups medium yields (42 – 56 %), and with α-branched diacyl peroxides moderate yields (20 – 33 %). A comparison of the mixed Kolbe-electrolysis with the low temperature photolysis of the neat peroxide demonstrates the superiority of the latter method in small scale conversion with regard to yield and selectivity.     

Preparation and properties of poly(phosphonatoalanes)

Two general types of poly(phosphonatoalanes), [? Al(X)O? P(O)(R)O? ]_n (X = Cl or F, R = alkyl or aryl) and [? Al(OP(O)R₂)O? P(O)(R′)O? ]_n, were prepared and studied. Poly[chloro(phosphonato)alanes] are influsible and have low molecular weights (n = 4–11). Polyfluoro(phosphonato)alanes are fusible and also have low molecular weights, but under certain conditions grow to higher polymers (n = 30–45). Poly[phosphinato(phosphonato)alanes] are fusible and are prepared with high molecular weights (n = 83–340).     

Effects of methyl substituents on the proton chemical shifts in the NMR spectra of the twenty methyl and ethyl substituted hydrazines. Electronegativity values for hydrazyl groups

The C? H proton NMR spectra of the twenty conceivable methyl and ethyl substituted hydrazines are presented and analyzed with respect to effects on chemical shifts of the C? H protons caused by replacement of hydrogen by methyl and ethyl groups on the C? N? N? C chain. Thirteen different methyl substituent effects and six different ethyl substituent effects are identified and evaluated. Most of the effects are shielding and in accordance with an electron-releasing inductive effect of alkyl groups. A deshielding effect (the ‘C? C bond effect’) is observed when a methyl group replaces the hydrogen on the carbon bearing the hydrogen in focus and primary hydrogen on the carbon bearing the hydrogen in focus and primary hydrogens become secondary, as observed in other systems. On the basis of their effects on the chemical shifts of methyl protons in CH₃X, eighteen different hydrazyl groups (× = ? NR₁NR₂R₃) fall into three classes: I (R₁ = H; R₂, R₃ = H or alkyl); II (R₁ = alkyl; R₂ and/or R₃ = H); III (R₁, R₂ and R₃ = alkyl), with slightly different electronegativities: 2·94, 2·83 and 2·74, respectively.     

Retention Time of Unretained Compound Calculation and Determination of Retention Indices of Some Monosubstituted Benzenes Using a Multiparametric Method in Binary, Ternary and Quaternary Solvent RP-LC Systems

In reversed phase liquid chromatography (RP-LC), the validity of a multiparametric (MP) non-linear least-squares regression iterative method has been evaluated for 14 different aqueous mobile phases modified with one, two or three organic solvents [acetonitrile (ACN), methanol (MeOH), or tetrahydrofuran (THF)] for calculating the retention time of unretained compound t _M and the regression parameter (slope b), based on the use of alkan-2-ones and alkyl aryl ketones homologous series. The determination of t _M and b has been studied for eight binary (ACN?CH₂O or MeOH?CH₂O), 3 ternary (ACN?CMeOH?CH₂O) and 3 quaternary (ACN?CMeOH?CTHF?CH₂O) mobile phase systems on an Omnispher C₁₈ column. The multiparametric calculated t _M and b values were compared with those obtained by Guardino??s, and Grobler??s methods. The MP retention indices (RI) of ten monosubstituted benzenes with different functionality (hydroxyl, carbonyl, nitro, etc.) based on the alkan-2-ones retention index standards have been determined and compared for the different mobile phase compositions studied. The influence of organic modifier type, the nature of mobile phase system and water content on the variation of retention parameter studied in this work were discussed.     

No Fear of Perfluorinated Peroxides: Syntheses and Solid‐State Structures of Surprisingly Inert Perfluoroalkyl Peroxides

We report on the solid‐state structures of bis(nonafluoro‐tert‐butyl) peroxide [(F₃C)₃CO]₂ and bis(undecafluoro‐2‐methyl‐2‐butyl) peroxide [(C₂F₅)(F₃C)₂CO]₂. These peroxides were prepared from the corresponding hypofluorites and fluorinated silver wool. The solid‐state structures obtained after in situ crystallisation show unusual COOC dihedral angles of 180°, as well as elongated O?O bonds because of the bulky perfluorinated alkyl groups. The perfluorinated alkyl peroxides are insensitive to both impact (>40 J) and friction (>360 N), and resistant towards mineral acids (HX; X=F, Cl, Br) and elemental halogens (X₂). Ferrocene is oxidized by [(F₃C)₃CO]₂ to [Fe^IIICp₂][OC(CF₃)₃].     

Homogeneous Ziegler–Natta catalysis. II. Ethylene polymerization by IVB transition metal complexes/methyl aluminoxane catalyst systems

Homogeneous Ziegler-Natta systems for the ethylene polymerization, deriving from R₂R_2′M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied. Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported. On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds. Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization. The catalytic activity of the systems under investigation was strongly affected also by changing both the σ-alkyl and the π-cyclo-pentadienyl ligands. Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ-alkyl derivatives of IVB transition metals, such as Zr(CH₂C₆H₅)₄, are also able to polymerize ethylene with a fairly high productivity. Active species containing Zr? O? Al bonds have been postulated.     

Role of Radical Elimination Reactions with Concerted Fragmentation in the Chain Decomposition of Alkyl Nitrates

The reactions X? + HCR₂ONO₂ → XH + R₂C=O + ?NO₂ are very exothermic due to the cleavage of the weak N?O bond and the formation of the energy-intensive C=O bond. The quantum chemical calculation of the transition state of these reactions for X? = Et? and EtO? used as examples showed that they actually proceed in one elementary act as eliminations with concerted fragmentation. The kinetic parameters were estimated within the framework of the intersecting parabolas model; the parameters allow the calculation of the activation energy and rate constant from the enthalpy of the above reaction. For a series of reactions involving the Et?, EtO?, RO?₂, and ?NO₂ radicals, on the one hand, and a number of alkyl nitrates, on the other, their enthalpies, activation energies, and rate constants were calculated. Based on the data obtained, new kinetic schemes of the chain decomposition of alkyl nitrates involving eliminations with fragmentation were proposed.     

Gas Phase Structures of Peroxides: Experiments and Computational Problems

Gas‐phase structures of several organic and inorganic peroxides X‐O‐O‐X and X‐O‐O‐X′, which have been determined experimentally by gas electron diffraction and/or microwave spectroscopy, are discussed. The O?O bond length in these peroxides varies from 1.481(8) Å in Me₃SiOOSiMe₃ to 1.214(2) Å in FOOF and the dihedral angle ?(XO‐OX) between 0° in HC(O)O‐OH and near 180° in Bu^tO‐OBu^t. Some of the peroxides cause problems for quantum chemistry, since several computational methods fail to reproduce the experimental structures. Extreme examples are MeO‐OMe and FO‐OF. In the case of MeO‐OMe only about half of the more than 100 computational methods reported in the literature reproduce the experimentally determined double‐minimum shape of the torsional potential around the O?O bond correctly. For FO‐OF only a small number of close to 200 computational methods reproduce the O?O and O?F bond lengths better than ±0.02 Å.     

EPR studies on electron transfer reactions between O-benzoyl-N-alkylhydroxylamines and perfluoroacyl peroxides. Generation of n- and sec-alkyl perfluoroacyl nitroxides and sec- and tert-alkyl perfluoroalkyl nitroxides

Both EPR studies and product analysis have disclosed that the oxidation of O-benzoyl-N-alkylhydroxylamines (1, 4, 7) by perfluoroacyl peroxides (2) is an electron transfer-initiated process. Depending on the nature of the alkyl groups in the substrates, the caged radical pair CP₁ (RN OCOPh, R_fCOO) may react through different radical pathways resulting in different nitroxides along with the neutral products. With primary, benzyl and secondary alkyl groups, a 1,2-acyl shift becomes the predominant pathway resulting in acyl nitroxides (3, 5). With tert-alkyl groups such as tert-butyl, tert-alkyl perfluoroalkyl nitroxides (8) are formed via β-scission of both RN*OCOPh and R_fCOO*. A general mechanistic pathway is proposed for the titled reactions generating the quite useful fluorinated nitroxides.     

The chemistry of diacyl peroxides IX. An ESR study of the reduction of polyfluorodiacyl peroxides by copper (O) in the presence of 2-nitro-2-nitrosopropane: The generation of polyfluoroalkyl nitroalkyl nitroxides

Polyfluoroalkyl radicals generated by one-electron reduction of polyfluorodiacyl peroxides by copper (O) were trapped by 2-nitro-2-nitrosopropane to yield polyfluoroalkyl nitroalkyl nitroxides, R_FN(O)CMe₂NO₂.     

Carbon-13 magnetic resonance spectra of quaternary ammonium salts derived from enamino ketones

¹³C magnetic resonance spectra of nine quaternary ammonium salts of the general formula R¹C¹(O)C²H?C³HNR₃⁴Cl (where R¹, R⁴ = alkyl) were obtained and compared with those of the parent amino compounds. The chemical shift differences between these two classes of compounds are qualitatively accounted for by π-electron density changes. Steric effects and hyperconjugation of the alkyl substituents are also discussed.     

Neue Methoden zur Chlorierung von Organophosphorverbindungen mit P?H-Funktionen

New Methods for the Chlorination of Organophosphorus Compounds with P? H-Functions Starting from compounds containing a P? H bond, which are obtained by the addition of PH₃ to olefinic double bonds, novel methods are described for the synthesis of phosphonous and phosphinous acid chlorides as well as of phosphonic, phosphinic, and thiophosphinic chlorides. Compounds of the type RPH₂, R₂PH, R₂P(:O)H, and R₂P(:S)H (R = alkyl, cycloalkyl, aryl) are converted into the correspondent halogenated substances by means of C₂Cl₆ or PCl₅ without addition of base. Direct oxychlorination of prim. and sec. phosphines to phosphonic and phosphinic chlorides is achieved by SO₂Cl₂.     

Collision-Induced dissociations of deprotonated peptides. Dipeptides containing aspartic or glutamic acids

Deprotonated dipeptides, on collisional activation, fragment by the characteristic process NH₂CH(R¹) CONHCH(R²)CO₂^? → NH₂^?C(R¹)CONHCH(R²)CO₂H → ^?NHCH(R²)CO₂H + NH₂C(R¹)?C?O, when R¹ and R² = H or alkyl. However, when one of the constituent amino acids is either aspartic acid or glutamic acid, the standard cleavage becomes minor in comparison with fragmentation through the α-side-chain of Asp or Glu. For example, [Asp-Leu - H]^? and [Leu-Asp - H]^? both fragment principally by loss of water, a fragmentation not normally noted for peptides. In addition, [Leu-Asp - H]^? loses CO₂ and also forms HO₂CCH?CHCO₂^?˙. These fragmentations establish that Asp is the C-terminal amino acid. In contrast, isomeric Glu dipeptides, e.g. [Glu-Ala - H]^? and [Ala-Glu - H]^? undergo similar fragmentation, both competitively losing H₂O and CO₂. Both spectra also contain a product ion at m/z 128, identified as the pyroglutamate anion. Product ion and deuterium-labelling studies have been used in an attempt to elucidate the complex fragmentation mechanisms in these systems.     

Über Chalkogenolate. 81. Untersuchungen über N-Hydroxydithiocarbamidsäure 3. Ester der N-Hydroxydithiocarbimidsäure und -carbamidsäure

On Chalcogenolates. 81. Studies on N-Hydroxy Dithiocarbamic Acid. 3- Esters of N-Hydroxy Dithiocarbimic Acid and Dithiocarbamic Acid The reaction between hydroxylamine, carbon disulfide, and alkyl halide leads to the corresponding ester of N-hydroxy dithiocarbimic acid HO? N?C(SR)₂ with R = CH₃, C₂H₅; R₂ = ? CH₂? CH₂? . The phenyl ester of N-hydroxy dithiocarbamic acid HO? NH? CS(SC₆H₅) has been prepared by reaction of hydroxylammonium chloride with the phenyl ester of chlorodithioformic acid. N-Methyl hydroxylammonium chloride reacts with carbon disulfide and alkyl iodide to form the corresponding ester of the dithiocarbamic acid HO? N(CH₃)? CS(SR) with R = CH₃, C₂H₅. The unstable compounds have been characterized by different methods.     

Mass spectrometry in structural and stereochemical problems—CLXXI: Factors governing the preferential loss of small vs. Large radicals in the α-fission of aliphatic amines

A study of the α-cleavage processes of aliphatic amines (using R_LCH₂N(R)CH₂R_s and R_LCH(NR)R_s

1 R_L represents the larger R_s the smaller alkyl group throughout this paper and both, unless indicated to the contrary, have similar degrees of lsubstitution on the α-carbon atom.

as typical substrates) at several ionizing voltages indicates that the loss ratio of large and small alkyl radicals, [M ? R_L]/[M ? R_s], decreases with ionizing voltage. This ratio, greater than 1·0 at 70 eV, may become less than unity at low voltage (15 eV, 10 eV) in some cases. Comparison of similarly structured compounds with nitrogen or oxygen as the heteroatom suggests that the effects of ionizing voltage are lessened when the fragment is of greater stability (e.g. amine vs. ether or imine vs. ketone). The effects of lowering the ionizing voltage became much less pronounced as the alkyl groups become larger or similar in size.