Photofragmentation of alpha-oxocarboxylic acids in aqueous solution. An EPR study. Formation of semidione radicals by decarboxylative substitution of alpha-oxocarboxylic acids by acyl radicals--II. Oxaloacetic acid (oxosuccinic acid).

Abstract— –On in situ photolysis (Λ= 250–400 nm) of aqueous oxaloacetic acid solutions, between pH 5 and 10, the radicals ^-O₂CCH₂C(O^->=C(O⁺)CH₂CO₂^- and ^-O₂CCH₂C(OH)CO₂ are identified. With acetone present, CH₂CO₂, CH₃C(OH)CO^-₂, CH₃C(O^-)=C(O)CH₂CO₂ and -O₂CCHCOCO₂ are also observed. CO₂ and CO are identified as reaction products. The experimental results are explained in terms of α-cleavage of the electronically excited keto-isomer dianion of oxaloacetic acid to yield O₂CCH₂CO and CO₂^-. ^-O₂CCH₂CO adds to the keto-isomer of oxaloacetic acid and to pyruvic acid, which is formed from oxaloacetic acid by thermal decarboxylation, to yield ^-O₂CCH₂C(O^-)= C(O^-)CH₂C0^- and CH₃C(O^-)=C(O)CH₂CO^-₂, respectively, via a decarboxylase substitution reaction. CH₂CO₂ is derived from ^-O₂CCH₂CO by decarbonylation. CO₂^- is scavenged by oxaloacetic acid and pyruvic acid to yield O₂CCH₂C(OH)CO₂ and CH₃C(OH)CO₂^-, respectively.     

Syntheses of σ-cyclobut-1-en-3-onyl complexes by cycloaddition of ketenes to some transition metal alkynyl complexes

Reactions of ketenes (R¹R²CCO) with (η⁵-C₅H₅)Ni(PPh₃)CCR (I) and (η⁵-C₅H₅)Fe(CO)(L)CCR (III, L = CO and PPh₃) give σ-cyclobut-1-en-3-onyl complexes, {(η⁵-C₅H₅)Ni(PPh₃)$\text{CC(R)COC}$}R¹R² (VI) and (η⁵-C₅H₅)Fe(CO)(L)$\text{CC(R)COC}$R¹R² (IX)}, (2 + 2) cycloaddition products, in good yields. The σ-cyclobutenonyl complexes also can be prepared by the reaction of I and III with acyl chlorides in the presence of triethylamine.     

On the reaction of metallated acetylenes and allenes with carbon disulfide. Influence of the alkali metal counter-ion and the substituents in the acetylene and allene on the course of the reaction

Addition at low temperatures of carbon disulfide to a solution of the lithium compound

(R¹ = CH₃, C₃H₇, Ph, OCH₃, SCH₃) results in the initial formation of an allenic carbodithioate H₂CCC(R¹)CSSLi, while for R¹ = t-C₄H₉ or SiMe₃ acetylenic carbodithioates R¹CCCH₂CSSLi are formed. The initial products undergo very rapid subsequent reactions. For R¹ = CH₃ or C₃H₇ the lithium compound adds (in the allenic form) in a conjugated fashion to the CCCS system of the allenic carbodithioate. The acetylenic dithioates are deprotonated to give the geminal dithiolates R¹CCCHC(SLi)₂. For R¹ = Ph, OCH₃ or SCH₃, subsequent deprotonation at the terminal carbon atom of the initial allenic dithioate gives enyne dithiolates HCCC(R¹)C(SCH₃)₂; this reaction proceeds more satisfactorily with the potassium compounds.     

Synthesis of cross linked platinum metal containing polyyne polymers

Reaction of Pt(PⁿBu₃)₂Cl₂ (1) or Pt(AsⁿBu₃₂Cl₂ (2) with stoichiometric amounts of 1,3,5-triethynylbenzene, [1,3,5-(H? C?C? )₃C₆H₃] (3)yields monomeric, [1,3,5-Cl(PⁿBu₃)₂(Pt? C? C? )₃C₆H₃] (4), [1,3,5-(C1)(AsⁿBu₃)₂Pt? C? C? ₃C₆H₃] (5) or polymeric, {1,3,5-[(PⁿBu₃)₂Pt? C?C? ]₃C₆H₃? )ⁿ (6), {1,3,5-[(AsⁿBu₃)₂Pt? C? C? ]₃C₆H₃? }ⁿ (7) complexes. Treatment of (1) with (3) and 2,5-diethynyl-p-xylene,H? C? C? C₆H₂(CH₃)₂? C? C? H (8) in varying molar ratios yields a series of high molecular weight cross linked platinum metal containing polyyne copolymers.     

Gallium “Shears” for C=N and C=O Bonds of Isocyanates

Digallane [L¹Ga−GaL¹] ( 1 , L¹=dpp-bian=1,2-[(2,6-iPr₂C₆H₃)NC]₂C₁₂H₆) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C−N−Ga fragments to afford [L¹(O=C−NR)Ga−Ga(RN−C=O)L¹] (R=Ph, 3 ; R=Tos, 4 ). The reactions with both isocyanates result in new C−C and N−Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C−N−Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga−N bond of the same fragment to afford compound [L¹Ga−Ga(AllN− C=O)₂L¹] ( 5 ) (All=allyl). In the presence of Na metal, the related digallane [L²Ga−GaL²] ( 2 ; L²=dpp-dad=[(2,6-iPr₂C₆H₃)NC(CH₃)]₂) is converted into the gallium(I) carbene analogue [L²Ga:]⁻ ( 2 A ), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na₂(THF)₅]{L²Ga[EtN−C(O)]₂GaL²} ( 6 ), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF)₂]₂[L²Ga(p-MeC₆H₄)(N−C(O))₂−N(p-MeC₆H₄)]₂ ( 7 ), cleavage of the C=O bond to yield the di-O-bridged digallium compound [Na(THF)₃]₂[L²Ga-(μ-O)₂-GaL²] ( 8 ), and generation of the further addition product [Na₂(THF)₅][L²Ga(CyNCO₂)]₂ ( 9 ). Complexes 3 – 9 have been characterized by NMR (¹H, ¹³C), IR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their electronic structures have been examined by DFT calculations.     

The influence of the temperature on the formation of samarium nitrato complexes

The stability constants of the Sm(NO₃)²⁺ complex were determined at three temperatures, using the solvent extraction method. It was found that:K ₁ ⁰ =63.6 at 17°C, 30.3 at 35°C, 20.1 at 50°C. This corresponds with the formation of a Sm(H₂O)(NO₃)²⁺ complex at 17°C and a Sm(H₂O)₂(NO₃)²⁺ complex at 50°C.

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Der Einfluß der Temperatur auf die Bildung von Samarium Nitrato Komplexen

Zusammenfassung Die Stabilitätskonstanten von Sm(NO₃)²⁺ Komplexen wurden mittels der Lösungsmittelextraktionsmethode bei drei Temperaturen bestimmt. Dabei ergab sichK ₁ ⁰ =63.6 bei 17°C, 30.3 bei 35°C und 20.1 bei 50°C. Das entspricht der Bildung eines Sm(H₂O)(NO₃)²⁺ Komplexes bei 17°C und eines Sm(H₂O)₂(NO₃)²⁺ Komplexes bei 50°C.

     

Thermodynamic properties of peptide solutions 4. Partial molar volumes and heat capacities of aqueous solutions of some glycyl dipeptides

Partial molar volumes, V ₂ ^o and partial molar heat capacities C _p,2 ^o have been determined in aqueous solution at 25°C for the dipeptides glycyl-L-asparagine, glycyl-DL-threonine, glycyl-DL-serine and glycyl-DL-phenylalanine. These results, along with those for some other dipeptides of sequence Gly-X, were used to estimate side chain contributions to V ₂ ^o and C _p,2 ^o . For these dipeptides both V ₂ ^o and C _p,2 ^o were found to be a linear function of the respective thermodynamic property for the amino acid X. The contributions of the glycyl units to V ₂ ^o and C _p,2 ^o of the dipeptide are discussed.     

Gas-phase electron diffraction determination of the molecular structure of perfluoro(methyloxirane)

The molecular geometry of perfluoro(methyloxirane) has been studied using gas-phase electron diffraction data, effective least-squares refinement of the structure being achieved with the aid of constraints to limit the number of variable parameters. With the CCF₃ bond constrained to be 0.078 Å longer than the ring CC, the refined bond- length values CF (av.) = 1.323(2), CO (av.) = 1.410(8), and CC (ring) = 1.467(7) Å ($\text{r}$_g values, with e.s.d. in parentheses) were obtained; the angles between ring bonds and substituent CF bonds were CCF (av.) 121(1) and OCF (av.) 114(1)^o, the corresponding parameters involving the bulkier CCF₃ fragment being larger by 3^o in each case [∠CCCF₃ 124(1)^o∠OCCF₃ 117(2)^o]. The remaining refined parameters were ∠CCF(of CF₃) = 110.6(4)^o and τ , a torsion angle defining the orientation of the CF bonds of the CF₃ group with respect to ring bonds, = 29(2)^o. Dependent bond angles possessed the values 62.7 (COC), 58.7 [OCC (ring)], 108.3 [FCF (CF₃ group)], 114 [FCF (ring CF₂)], and 111^o (FCCF₃).     

Spark source mass spectrometric calibration of the local vibrational mode absorption of carbon in gallium arsenide on arsenic sublattice sites

An appropriate calibration of the local vibrational mode absorption of carbon in GaAs on arsenic sublattice sites, C_As, at wavenumber 582 cm^–1 (77 K) is presented. Integrated absorptions I_α of C_As, the dominant acceptor in undoped monocrystalline GaAs, and calibrated carbon concentrations [C] were measured in single crystals using the methods FTIR and SSMS, respectively. A calibration factor f_C = [C]/I_α of (7.1 ± 0.2) × 10¹⁵ cm^–1 has been derived for 2.8 × 10¹⁴ cm^–3≤ [C] ≤ 1.4 × 10¹⁶ cm^–3 above a SSMS detection limit of [C]_DL? 1.4 × 10¹³ cm^–3. The carbon concentrations [C] = [C]_SSMS/RSC_C were calibrated with a relative sensitivity coefficient RSC_C = [C]_SSMS/ [C]_TRUE of 3.1 ± 0.1. CPAA was used as a reference method for [C]_CPAA≥ 4.4 × 10¹⁴ cm^–3 in order to approximate [C]_TRUE.     

Production of highly enriched Carbon-13 by IR multiphoton dissociation of dichlorodifluoromethane mixed with hydrogen iodide

Isotope-selective IR multiphoton dissociation of CF₂C1₂ molecules in a mixture with HI was experimentally investigated. It was shown that irradiation of the CF₂C1₂-HI mixture leads to the successive buildup of the intermediates CF₂HC1 and CF₂HI, which also isotopically selectively dissociate simultaneously with the substrate to yield the final product CF₂H₂ enriched in¹³C up to 97% at an initial¹³C concentration of 1.1% in CF₂C1₂. When CF₂C1₂ preliminarily enriched in¹³C up to 12.3% was used, the attained¹³C concentration in CF₂H₂ was as high as ≥99%. Isotopic selectivity and dissociation yields of¹³C- and¹²C-containing components of the substrate CF₂C1₂ and both intermediate dissociation products, CF₂HC1 and CF₂HI, were measured, depending on experimental conditions. The¹³C distribution over the intermediate and final dissociation products was studied. The side products C₂F₄C1₂ and CF₂IC1 were detected.     

Substituent effects on nuclear spin–spin carbon–carbon coupling constants in derivatives of acetylene

¹J(¹³C?¹³C) nuclear spin–spin coupling constants in derivatives of acetylene have been measured from natural abundance ¹³C NMR spectra and in one case (triethylsilyllithiumacetylene) from the ¹³C NMR spectrum of a ¹³C-enriched sample. It has been found that the magnitude of J(C?C) depends on the electronegativity of the substituents at the triple bond. The equation ¹J(¹³C?¹³C) = 43.38 E_x + 17.33 has been derived for one particular series of the compounds Alk₃SiC?CX, where X denotes Li, R₃Sn, R₃Si, R₃C, I, Br or Cl. The ¹J(C?C) values found in this work cover a range from 56.8 Hz (in Et₃SiC?Li) to 216.0 Hz (in PhC?CCI). However, the ¹J(C?C) vs E_x equation combined with the Egli–von Philipsborn relationship allows the calculation of the coupling constants in Li₂C₂ (32 Hz) and in F₂C₂ (356 Hz). These are probably the lowest and the highest values, respectively, which can be attained for ¹J(CC) across a triple bond. The unusually large changes of the ¹J(C?C) values are explained in terms of substituent effects followed by a re-hybridization of the carbons involved in the triple bond. INDO FPT calculations performed for two series of acetylene derivatives, with substituents varied along the first row of the Periodic Table, corroborate the conclusions drawn from the experimental data.     

Loss of methyl from [H2CC(OH)?CH3]+˙ ions prepared by electron impact ionization of unstable 2-hydroxypropene

Unstable 2-hydroxpropene was prepared by retro-Diels-Alder decomposition of 5-exo-methyl-5-norbornenol at 800°C/2 × 10^?6 Torr. The ionization energy of 2-hydroxypropene was measured as 8.67±0.05 eV. Formation of [C₂H₃O]⁺ and [CH₃]⁺ ions originating from different parts of the parent ion was examined by means of ¹³C and deuterium labelling. Threshold-energy [H₂C?C(OH)? CH₃]^+˙ ions decompose to CH₃CO⁺+CH₃^˙ with appearance energy AE(CH₃CO⁺) = 11.03 ± 0.03 eV. Higher energy ions also form CH₂?C?OH⁺ + CH₃ with appearance energy AE(CH₂?C?OH⁺) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C₂H₃O]⁺ ions containing the original methyl group and [CH₃]⁺ ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate-determining isomerization [H₂C?C(OH)? CH₃]^+˙ →[CH₃COCH₃]^+˙, followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed.     

Nucleophilic substitution reactions of acetylides on substituted tricarbonyl(η6-fluoroarene)chromium and reactions of tricarbonyl[η6-(2-trimethylsilylethynyl)toluene]chromium and tricarbonyl[η6-(p-ethynyl-phenylethynyl)benzene]chromium with dicobalt octacarbonyl

Nucleophilic substitution reactions of various acetylides on substituted tricarbonyl(η⁶-fluoroarene)chromiums were pursued. The reaction presumably underwent a more complicated mechanism rather than the direct substitution on the fluorine-bearing carbon. The organometallic compounds (η⁶-C₆H₃R¹R²R³)Cr(CO)₃ (R¹: CC–C₆H₄CH₃, R²: o-Me, R³: H (5a), R¹: CC–C₆H₄CH₃, R²: o-OMe, R³: H (6a), R¹: CC–C₆H₄CH₃, R²: m-OMe, R³: H (6b), R¹: CCPh, R²: o-Me, R³: o-OMe (8b), R¹: CCPh, R²: m-Me, R³: m-OMe (8c), R¹: CCSiMe₃, R²: o-Me, R³: H (9a), R¹: CC–C₆H₄CCH, R²: H, R³: H (12), R¹: CC–C₆H₄CCH, R²: o-Me, R³: H (13)) as well as the organometallic dimmer [{(η⁶-o-Me-C₆H₄)Cr(CO)₃(di-ethynyl)] (di-ethynyl: CC–C₆H₄CC (14)) have been synthesized from nucleophilic substitution reactions of tricarbonyl(η⁶-fluoroarene)(chromium) compounds with suitable acetylides. The products have been characterized by spectroscopic means. In addition, (8b) and (8c) were characterized by X-ray diffraction studies. Further reactions of (9a) and (12) with appropriate amount of Co₂(CO)₈ yielded μ-alkyne bridged bimetallic complexes, Co₂(CO)₆{μ-Me₃SiCC–(o-tolueneCr(CO)₃} (10) and (Co₂(CO)₆)₂{μ-HCC–C₆H₄–CC–(benzene)Cr(CO)₃)}(15), respectively. Both (10) and (15) were characterized by spectroscopic means as well as single crystal X-ray crystallography. The core of these molecules is quasi-tetrahedron containing a Co₂C₂ unit. A two-dicobalt-fragments coordinated di-enyls complex, (Co₂(CO)₆)₂{μ-HCC–C₆H₄–CC–H} (17), was synthesized from the reaction of 1,3-diethynylbenzene with Co₂(CO)₈. Crystallographic studies of (17) also show that it exhibits a distorted Co₂C₂ quasi-tetrahedral geometry.     

Formation and fragmentation of C n + clusters produced from a C60/C70 mixture in an electron-impact ion source

Various fullerene ions are generated in a standard plasma ion source from a vaporized mixture of C₆₀/C₇₀. Except C ₆₀ ⁺ and C ₇₀ ⁺ , the fullerene ions are formed by fragmentation of C₆₀ or C₇₀ excited by electron impact. Information on the structure and stability of the fullerene ions is obtained by studying unimolecular dissociation and collision-induced fragmentation of C ₆₀ ⁺ , C ₅₈ ⁺ and C ₅₆ ⁺ in H₂ and Ar target gases.     

1H and 13C NMR study of α-acetylenic PIII and PIV derivatives. Signs and magnitudes of J(P?C) and J(P?H)

All J(P? H) and J(P? C) values, including signs, have been obtained in acetylenic and propynylic phosphorus derivatives, R₂P(X)? C?C? H and R₂P(X)? C?C? CH₃ (X ? oxygen, lone pair and R ? C₆H₅, N(CH₃)₂, OC₂H₅, N(C₆H₅)₂, Cl) from ¹H and ¹³C NMR spectra. In P^IV derivatives the following signs are obtained: ¹J(P? C)+, ²J(P? C)+, ³J(P? C)+, ³J(P? H)+, ⁴J(P? H)? . Linear relations are observed between ¹J(P? C), ²J(P? C) and ³J(P? C) versus ³J(P? H), indicating that these coupling constants are mainly dependent on the Fermi contact term, though the other terms of the Ramsey theory do not seem to be negligible for ¹J(P? C) and ²J(P? C). In P^III derivatives these signs are: ¹J(P? C)- and +, ²J(P? C)+, ³J(P? C)-, ³J(P? H)-, ⁴J(P? H)+. Only ³J(P? C) and ³J(P? H) reflect a small contribution of the Fermi contact term while in ¹J(P? C) and ²J(P? C) this contribution seems to be negligible relative to the orbital and/or spin dipolar coupling mechanisms.     

FTIR study of the Cl-atom initiated oxidation of methylglyoxal

The kinetics and mechanism of Cl-atom initiated reactions of CH₃C(O)CHO were studied using the FTIR detection method in the photolysis (λ < 300 nm) of Cl₂? CH₃C(O)CHO mixtures in 700 torr of N₂? O₂ diluent at 298 ± 2 K. The observed product distribution over the O₂ pressure range from 0–700 torr, combined with relative rate measurements, provided evidence that: (1) the primary step is Cl + CH₃C(O)CHO → HCl + CH₃C(O)CO with a rate constant of (4.8 ± 1.1) × 10^?11 cm³ molecule^?1 s^?1; and (2) the predominant fate of the primary radical CH₃C(O)CO under atmospheric conditions is unimolecular dissociation to CH₃C(O) radicals and CO, rather than O₂-addition to yield the corresponding carbonylperoxy radical CH₃C(O)C(O)OO.     

Selenoketene substitution structure

Microwave studies (26.5–40 GHz) of further isotopic species of selenoketene formed by pyrolysis of 1,2,3-selenodiazole (¹²CH₂¹²C^76,77,82Se, ¹²CH₂¹³C⁸⁰Se and ¹³CH₂¹²C⁸⁰Se) and by pyrolysis of 5-deuterio-1,2,3-selenodiazole (¹²CHD¹²C^78,80Se) are reported. In conjunction with earlier results for ¹²CH¹²C^78,80Se an r_s structure has been derived with distances SeC (1.706 Å), CC (1.303 Å), CH (1.0908 A) and a HCH bond angle of 119.7°. The geometry of the CH₂C moiety of selenoketene is closer to allene, CH₂CCH₂, than to ketene, CH₂CO.     

Synthesis and multinuclear NMR data of the ferrocenes (Me3Ecp)2Fe (E = C,Si, Ge,Sn, Pb)

The substituted cyclopentadienyl anions Me₃Ecp⁻ with E = C, Si, Ge, Sn, Pb have been prepared from either the mono- or disubstituted cyclopentadienes, including the hitherto unknown (Me₃Pb)₂C₅H₄. Representative examples have been characterized by ¹³C NMR spectroscopy. Treatment with iron(II) chloride yielded the ferrocenes (Me₃Ecp)₂Fe, which have been investigated by ¹H, ¹³C, ²⁹Si, ¹¹⁹Sn, and ²⁰⁷Pb NMR spectroscopy. ¹³C¹³C coupling and selective proton decoupling were used for the assignment of the ¹³C and ¹H signals. The shifts δ(¹³C) reflect the electron-releasing or -withdrawing power of the substituents Me₃E, but the isotope shifts ¹Δ¹³C(i)(¹³C(j)) do not show a similar trend. There is evidence that δ(¹¹⁹Sn) and δ(²⁰⁷Pb) are influenced by the coordination. The analysis of the coupling constants reveals that ¹J(¹³C(1)¹³C(2/5)) varies with the electronegativity of E. Because of the small range (4.5–5.0 Hz) of ¹J(⁵⁷Fe¹³C) the effect of E is apparent only when E = C is replaced by E = Si. As for the coupling between E and ¹³C or ¹H, the square root of the reduced coupling constant K is related linearly to the atomic number of E; exceptions are ¹K(²⁰⁷Pb¹³C).     

The effect of the nitrogen non-bonding electron pair on the NMR and X-ray in 1,3-diazaheterocycles

The effect of the nitrogen nonbonding electron pair on the ¹J_C,H values of 1,3-diazaheterocycles was analyzed and compared to 1,5-diazabiciclo[3.2.1]octanes, which have a restricted conformation. The ¹J_C,H values were measured by observing the ¹³C satellites in the ¹H NMR spectra and then determining the ¹H-coupled ¹³C NMR spectra. The ¹J_C,H values are 10 Hz larger when the α-hydrogen is synperiplanar rather than antiperiplanar to the nonbonding electron pair on the nitrogen, which serves as experimental evidence of the orbital n_N→σ¹_C,Hap interactions. In addition, the homoanomeric effect from the interactions of the nitrogen lone pair with the antibonding orbital of the equatorial hydrogen, which was in the β position, was discussed (n_N→σ¹_C(β),Heq).     

Unimolecular and collision-induced dissociation reactions of peracetylated methyl glucopyranoside

The mechanism of the collision-induced fragmentation of peracetylated methyl-α-D-glucopyranoside was investigated using deuterium-labelled acetates and sequential mass spectrometry. Loss of the substituent at C(1), the anomeric carbon, yields an ion of m/z 331, [C₁₄H₁₉O₉]⁺. This ion further dissociates via two pathways, the first including m/z 271, [C₁₂H₁₅O₇]⁺, 169, [C₈H₉O₄]⁺ and 109, [C₆H₅O₂]⁺, and the second including m/z 211, [C₁₀H₁₁O₅]⁺, 169, [C₈H₉O₄]⁺ and 127 [C₆H₇O₃]⁺. The first path proceeds via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4), and ending with loss of acetate from C(6). The second path proceeds predominantly via loss of acetates from C(3) and C(4), elimination of ketene from the C(2)-acetate and finally loss of ketene from the acetate at C(6). This path is also characterized by an ill-defined series of parallel decomposition reactions involving acetates from other sites on the molecule. At low collision energy, and in the absence of collision gas (unimolecular reaction conditions), the former pathway predominates; m/z 331 dissociates via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4).