Carbodications. 4.(1) Hydrogen Isotope Exchange of Crotonyl Cations in Superacid

The title ion reacts in 1:1 DF-SbF(5) and exchanges up to five protium atoms with deuterium. The incorporation of label was measured by GC-MS analysis of the methyl crotonate formed by methanol quenching. The isotopomer distribution at about 60% conversion, which shows a minimum for the d(1) and a maximum for the d(4) species, indicates that the intermediate dication with the second charge at C(3) loses a proton faster from C(4) than from C(2). Formation of the pentadeuteriocrotonyl cation indicates that the 1,4-dication (acyl primary alkyl) or the 1,2-dication must intervene in the process. Computer modeling of the kinetics for the multiple exchange process to fit the experimental deuterium distribution allowed determination of the relative rate constants and isotope effects (KIEs) for the formation of the carbocations from alkenoyl cations (beta-secondary KIE) and elimination from carbodications to alkenoyl cations (primary KIE). An exceptionally large beta-secondary KIE of ca. 2.0/hydrogen was found for the formation of the dication. A small primary isotope effect of ca. 1.5 was found for elimination from the dications to the alkenoyl cations. Elimination from the 1,3-acylalkyl dication to form the nonconjugated 3-butenoyl cation is 6-7 times faster than elimination to the conjugated 2-butenoyl cation. The rate ratio for the conversion of 3-butenoyl cation to the 1,4-dication (primary alkyl cation) and 1,3-dication (secondary alkyl cation) is (0.025-0.030):1, whereas the relative rate of the formation of the 1,2-acylalkyl dication (the alternative route of achieving pentadeuteration) is zero.     

Synthesis and crystal structure of cobalt(III) α-dioximates with pyrazine

A series of new coordination compounds of cobalt(III) trans-dioximates with pyrazine [CoCl(DH)₂Pz] · H₂O (I), [CoBr(DH)₂Pz] · H₂O (II), [Co(DH)₂Pz₂]NO₃ · H₂O (III), [Co(DH)₂Pz₂][BF₄] (IV), [Co(MgH)₂Pz₂][BF₄] (V), and [Co(NioxH)₂Pz₂][BF₄] (VI), where DH, MgH, and NioxH are dimethylglyoxime, methylglyoxime, and 1,2-cyclohexanedionedioxime monoanions, respectively, Pz is a pyrazine molecule were synthesized. The structures of compounds I, II, and VI were determined by X-ray diffraction. The Co(III) environment in these compounds is octahedral and the pseudomacrocyclic (DioxH⁻)₂ fragment occurs in the equatorial plane. This fragment is stabilized by O-H…O hydrogen bonds. The neutral Pz ligand is monodentate in all three compounds.     

Mass spectrometry of heterocyclic compounds. I—the behaviour of some quaternary heterocyclic iodides under electron impact

The mass spectra of five quaternary heterocyclic iodides have been investigated. The main thermal process is the anhydro base formation by HI elimination. The influence of the second heteroatom, X, on the fragmentation mode of the thermally produced anhydro bases is analysed.     

Synthesis and structure of the product of bis-condensation of 4-methyl-2,6-diformylphenol with dimethyl N′,N′-hydrazine diacetate

Bis-condensation of 4-methyl-2,6-diformylphenol with dimethyl N′,N′-hydrazine diacetate gave product I. The structure of I was determined by X-ray analysis. The conformations of the two side chains of dimethyl N′,N′-hydrazine diacetate are significantly different. The position of one chain is fixed by the intramolecular H-bond of O−H.…N type. Due to its conformation, compound I is partly ready for complex formation with d-metals. Institute of Applied Physics, Academy of Sciences, Moldova Republic. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Struktumoi Khimii, Vol. 35, No. 3, pp. 91–98, May–June, 1994. Translated by L. Smolina     

Crystal and molecular structures of dimethyl 4-phenylthiosemicarbazidediacetate and its adduct with rhodium(II) acetate

The crystal structures of dimethyl 4-phenylthiosemicarbazidediacetate C₁₃H₁₇N₃O₄S (I) and its adduct [C₈H₁₂O₈Rh₂ (C₁₃H₁₇N₃O₄S)₂] (II) with rhodium(II) acetate are determined by X-ray diffraction analysis. The unit cell parameters of crystals I are as follows: a = 8.066(6) Å, b = 15.812(6) Å, c = 24.977(8) Å, β = 94.88(3)°, space group P2₁/n, and Z = 8. The unit cell parameters of crystals II are a = 8.513(1) Å, b = 16.055(1) Å, c = 16.071(3) Å, β = 104.99(1)°, space group P2₁/c, and Z = 2. In structure I, two crystallographically independent molecules considerably differ from each other in the mutual orientation of the structural fragments containing the ester groups. In the centrosymmetric dimeric complex II, the organic molecule I acts as a monodentate thio ligand and adopts only one conformation.     

Crystal and molecular structure of chloro-bis(1,2-cyclohexanedione-dioxime)triphenylphosphinecobalt(III)

The structure of chloro-bis(1,2-cyclohexanedionediaxwte)triphenylphosphinecobalt(III) [Co(NioxH)₂PPh₃Cl] was determined by X-ray diffraction analysis. The crystal is monoclinic, a = 17.049(3), b = 15.223(3), c = 11.032(3) å, Β = 87.44(2)?, R(hkl) = 0.068 for 2739 reflections with I ≥2Σ(I). The structure is molecular. In the octahedral complex, the cobalt(III) atom is coordinated by two NioxH residues (av Co-N = 1.876 å), the phosphorus atom (Co-P = 2.307 å), and the Cl^- union (Co-Cl = 2.260 å). In the crystal, there are weak intermolecular interactions C-H…Cl and C-H…O.     

Synthesis and structure of the mixed-ligand cobalt(III) complex [Co(DH)(Hthsc)2][SiF6] · 2.3H2O

The compound [Co(DH)(Hthsc)₂][SiF₆] · 2.3H₂O, where DH^? is a dimethylglyoxime residue and Hthsc is a thiosemicarbazide molecule, was synthesized and studied by X-ray diffraction. The coordination polyhedron of the central metal ion (distorted octahedron) is formed by two sulfur atoms, two nitrogen atoms of two Hthsc molecules coordinated in the bidentate mode, and two nitrogen atoms of the DH^? ligand. The positions of three metal rings are fixed by two intramolecular hydrogen bonds (N-H…O). A bifurcated system of intermolecular hydrogen bonds forms a framework structure in the crystal.