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  • 1990-1994  (1,650)
  • Physical Chemistry  (1,121)
  • crystal structure
  • 1
    Electronic Resource
    Electronic Resource
    Problems in the low-temperature synthesis of 92K Superconducting YBCO (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1671-1678 
    Details
    ISSN: 0392-6737
    Keywords: Effects of material synthesis ; crystal structure ; chemical composition ; Y-based compounds ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary YBCO with high granulometric perfection and low dispersion can be obtained by a low-temperature reaction (≈800°C) of atomic-scale dispersed powders, produced through the thermal decomposition of liquid precursors. As reacted such powders are tetragonal and not superconducting, but they transform into the high-T c phase after optimized annealing treatments. We describe the method we developed and the characteristics of the materials we achieved, and we discuss the main features of the process in the light of the current know-how.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462158
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  • 2
    Electronic Resource
    Electronic Resource
    The crystal and molecular structure of N-(methylsulfonyl)-N-(2,6)-(dimethylphenyl)methanesulfonamide (1994)
    Springer
    Journal of chemical crystallography 24 (1994), S. 759-762 
    Details
    ISSN: 1572-8854
    Keywords: Sulfonamide ; methanesulfonanilide ; crystal structure ; molecular structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound, crystallizes in the triclinic space group $$P\bar 1$$ witha=8.232(4),b=9.159(2),c=10.230(3)Å. α=74.07(3)°, β=72.50(4)°, γ=63.65(3)° andZ=2. The structure was solved by direct methods and refined by full matrix least squares methods toR=0.054 for 1817 observed reflections. The plane containing the nitrogen and sulfur atoms is perpendicular to the aromatic plane. One of the S−O bonds in each methanesulfonyl group is in nearly eclipsed conformation with the N−C bond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666966
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  • 3
    Electronic Resource
    Electronic Resource
    The crystal structure of calcium succinate monohydrate (1994)
    Springer
    Journal of chemical crystallography 24 (1994), S. 437-440 
    Details
    ISSN: 1572-8854
    Keywords: Ca(C4H4O4)·H2O ; pentagonal pyramid ; calcium succinate ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The crystal structure of calcium succinate monohydrate, Ca(C4H4O4)·H2O, has been determined by single crystal X-ray diffraction. The crystals are monoclinic witha=11.952(2),b=9.691(2),c=11.606(2)Å, β=108.81(1)°, space group C2/c,Z=8,V=1272.49 Å3,d m =1.80, andd c =1.818 Mg m−3. The structure was refined by full-matrix least-squares techniques toR=0.027,R w =0.040, for 829 reflections with1≥3δ(I). Ca is coordinated to seven oxygen atoms, and the coordination polyhedron is best described as a pentagonal bipyramid. One carboxylate group in the succinate ion is bonded to three different Ca ions, forming a four-membered chelate ring with one Ca ion is bonded to three different Ca ions, forming a four-membered chelate ring with one Ca ion and unidentate bridge bonds to two other Ca ions. The other carboxylate group is bonded to two Ca ions through unidentate bonds. The structure is highly polymeric. The general structural features are nearly identical to those of calcium adipate monohydrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666091
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis, characterization, and crystal structure of 1,3,7,9-tetramethylpyrido-[2,3-d∶6,5-d′]-dipyrimidine-2,4,6,8-tetrone (1994)
    Springer
    Journal of chemical crystallography 24 (1994), S. 465-468 
    Details
    ISSN: 1572-8854
    Keywords: Pyrimidine ; uracil ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A new and easy method for the preparation of 1,3,7,9-tetramethylpyrido-[2,3-d∶6,5-d′]-dipyrimidine-2,4,6,8-tetrone is described. The structure of this compound has been solved by means of X-ray diffraction methods. The chemical characterization by spectral (mass, ultraviolet, infrared, and proton nuclear magnetic resonance) and thermal (thermogravimetry and differential scanning calorimetry) method is also reported. The compound is monoclinic, space groupP21/c,a=12.720(5),b=13.688(7),c=8.079(2) Å, β=107.06(4)°,Z=4. The structure consists of discrete tricyclic molecules, stacking playing an important role in crystal packing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666096
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  • 5
    Electronic Resource
    Electronic Resource
    The W2Cl4(NHCMe3)2(PR 3)2 molecules (R 3=Me3, Et3, Pr n 3, Me2Ph) I. Their isomeric forms, interconversion proeesses, crystalline forms, and detailed molecular structures (1994)
    Springer
    Journal of cluster science 5 (1994), S. 11-36 
    Details
    ISSN: 1572-8862
    Keywords: Tungsten ; isomeric forms ; crystal structure ; triple bonds ; interconversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A thorough study of compounds with the formula W2Cl4(NHCMe3)2(PR3)2, withR 3=Me3, Et3, Prg n 3 Me2,Ph, is reported. In addition to the previously reported crystalline compounds, namely Ia,trans-W2Cl4(NHCMe3)2(PMe3)2 in space group Pmmn;3a,trans-W2Cl4(NHCM3)2(PEt3)2 in space group P21/a (or P21/c); and4,cis-W2Cl4(NHCMe3)2(PMe2Ph)2 in Pna21, we have obtained and structurally characterized the following new substances,1b,trans-W2Cl4,(NHCMe3)2(PMe2)2, space group P21/c,a= 12.233 (4) Å,b= 12.872 (4) Å,c=17.095 (5) Å,β=93.52 (2)°,Z=4,V=2687 (1) Å3 2,cis-W2Cl4(NHCMe3)2(PMe3)2, P21/c,a=9.673 (4) Å,b=17.249 (4) Å,c=16.244 (5) Å,β=99.63 (3),Z = 4 ,V=2669 (1) Å.3b,trans-W2Cl4(NHCMe3)2(PEt3)2, Pl,a=16.850 (3) Å,b=17.797 (3) Å,c= 11.459 (2)Å,α= 101.02 (1),β= 103.13°, y=84.23 (1)°,Z=4,V= 3279 (1) Å5,trans-W2Cl4(NHCM3)2(PMe2Ph)2, Fdd2,a=39.563 (8) Å at 20°C; 39.325 (10) Å at -6O°C,b = 57.543 (17) Å at 20°C; 57.186 (16) Å at -60°C,c= 8.810 (1) Å at 20°C; 8.770 (1) Å at - 60°C ,Z=24,V=20057 (7) Å3 (20°C), 19723 (8) Å3 ( - 60°C) .6,trans-W2Cl4(NHCMe3 2(PPrn 3)2, Pl,a= 17.287 (2) Å (20°C); 17.077 (5) Å (-60°C),b= 19.119 (2) Å (20°C); 18.952 (6) Å (-60°C),c= 12.713 (1) Å (20°C); 12.668 (4) Å (-60°C),Z=4,V= 3980 (1) Å3 (20°C), 3898 (2) ,Å3 ( - 60°C). In addition, the structure of3a was re-determined and refined so that the disorder ratio was a refined parameter, leading to a value of 0.520:0.480 instead of being arbitrarily fixed at 0.50:0.50. In all of the structures the molecules are held in eclipsed (but very distorted) rotational conformations and the W-W distances are all within the range of 2.305-2.330 Å. As will be shown in a later paper, for all phosphines, thecis andtrans isomers are of similar stability and an equilibrium mixture exists in solution. It is also shown that1a and3a do not contain unexpectedly short W-N bonds as previously reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165490
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  • 6
    Electronic Resource
    Electronic Resource
    A new platinum-osmium alkyne complex from the reaction of Pt2Os4(CO)18 with PhC ≡ CPh: The synthesis, characterization, and crystal structure of Pt2Os4(CO)8 (μ3-PhC2Ph)3(μ4-PhC2Ph) (1994)
    Springer
    Journal of cluster science 5 (1994), S. 317-326 
    Details
    ISSN: 1572-8862
    Keywords: Mixed metal cluster ; alkyne ; diphenylacetylene ; platinum ; osmium ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The new platinum-osmium alkyne cluster complex Pt2Os4(CO)8(μ3-PhC2Ph)3 (μ 4-PhC2Ph),2, was obtained from the reaction of Pt2Os4(CO)18,1b, with PhC2Ph and was characterized by IR.1H NMR and single-crystal X-ray diffraction analyses. The cluster of compound2 consists of an osmium capped Pt2Os3 square pyramid. It aLso contains three triply bridging and one quadruply bridging diphenylacetylene ligands. Crystal data for2: space group PI,a = 12.530(2) Å,b = 21.565(4) Å,c = 11.284(2) Å,α = 100.31(2),β = 111.89(1),β = 76.78(2),Z = 2, 3879 reflections,R = 0.032.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01170715
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  • 7
    Electronic Resource
    Electronic Resource
    Crystal structure oftrans-carbonylchlorobis-(tricyclohexylphosphine)iridium(I),trans-Ir(CO)Cl-[P(cyclo-C6H11)3]2, a disordered species (1994)
    Springer
    Journal of chemical crystallography 24 (1994), S. 557-560 
    Details
    ISSN: 1572-8854
    Keywords: Centrosymmetric ; symmetry ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the centrosymmetric triclinic space group $$P\bar 1$$ (C 1 l ; No.2) witha=9.9143(10) Å,b=10.2616(11) Å,c=10.7715(10) Å, α=113.887(8)°, β=109.197(8)°, γ=90.699(9)°,V=932.78(17) Å3 andZ=1. A total of 4869 data were collected and merged to a set of 2450 independent reflections; the structure was solved and refined toR=1.42% andwR=1.94%. The molecule lies on a site of $$\bar 1$$ symmetry and is disordered, with obvious scrambling of carbonyl and chloride ligands. Resulting bond lengths include Ir−P=2.339(1) Å, Ir−Cl=2.398(4) Å and Ir−CO=1.808(15) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666737
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  • 8
    Electronic Resource
    Electronic Resource
    Superconductivity in the tetragonal phase of La1.9Bi0.1CuO4+δ annealed under high oxygen pressure (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 37-38 
    Details
    ISSN: 1572-9605
    Keywords: High-Tc superconductivity ; La1.9Bi0.1CuO4+δ ; excess oxygen ; crystal structure ; superconducting transition temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have investigated the relation between the crystal structure and superconductivity in La1.9Bi0.1CuO4+δ , in which the phase separation observed in La2CuO4+δ is suppressed. A phase diagram in theT−δ plane is given for La1.9Bi0.1CuO4+δ with excess oxygen. For very smallδ values, the crystal structure is orthorhombic, and an orthorhombic-tetragonal phase transition occurs markedly atδ ∼ 0.03 in the measured temperature range between 13 and 293 K. Superconductivity is observed in the range of 0.04〈δ〈0.11. This is clear evidence thathigh-T c superconductivity also appears in the tetragonal phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730364
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  • 9
    Electronic Resource
    Electronic Resource
    Studies of crystalline native celluloses using potential energy calculations (1994)
    Springer
    Cellulose 1 (1994), S. 161-168 
    Details
    ISSN: 1572-882X
    Keywords: cellulose I ; molecular mechanics ; crystal structure ; molecular ; modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Energies for various trial packing arrangements of unit cells for the Iα and Iβ phases of native cellulose discovered by Sugiyamaet al. were evaluated. Both a rigid-ring method, PLMR, and the full-optimization, molecular mechanics program, MM3(90), were used. For both phases the models that had the lowest PLMR energy also had the lowest MM3 energy. Both calculated models have the chains packed ‘up’, O6s intg positions, and the same sheets of hydrogen-bonded chains. The Iβ structure model is essentially identical to that proposed previously for ramie cellulose by Woodcock and Sarko. It is also the same as the best parallel model previously proposed that was based on the X-ray data of Mann, Gonzalez and Wellard, once the various unit cell conventions are considered. Also, the energies from both methods for all three celluloses, Iα, Iβ and II, are in the order that rationalizes their relative stabilites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00819665
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of Configuration Around the Chiral Carbon Atoms on the Crystal Properties of Ephedrinium and Pseudoephedrinium Salicylates (1994)
    Springer
    Pharmaceutical research 11 (1994), S. 1549-1556 
    Details
    ISSN: 1573-904X
    Keywords: ephedrine ; pseudoephedrine ; salicylate ; chirality ; salt formation ; homochiral crystal ; racemic compound ; racemic conglomerate ; crystal structure ; conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The physicochemical properties and crystal structures of the crystalline salts formed by the interaction of an achiral anion, salicylate, with homochiral and racemic ephedrinium and pseudoephedrinium cations were determined. The interaction of ephedrinium or pseudoephedrinium with salicylate in aqueous solution yielded crystalline salts with the notable exception of homochiral ephedrinium. Evaporation of the solvent from solutions of homochiral ephedrine and salicyclic acid in various organic solvents, as well as grinding together solid homochiral ephedrine and solid salicylic acid, yielded viscous semisolids suggesting that homochiral ephedrinium salicylate has a low melting point and/or a high aqueous solubility. Mixing of the two viscous solids, obtained by grinding each of the opposite enantiomers of ephedrine with equimolar salicylic acid, resulted in the formation of racemic ephedrine and subsequently, upon heating, in the formation of racemic ephedrinium salicylate. While racemic ephedrinium salicylate exists as a crystalline compound (P21/n space group) with an equal number of opposite enantiomers in the unit cell, its diastereomer, racemic pseudoephedrinium salicylate, exists as a conglomerate, i.e. a physical mixture, of the homochiral crystals of the opposite enantiomers (each P21 space group). The inability of homochiral ephedrinium to exist as a crystalline salicylate salt at 20–25°C is attributed to its high energy conformation and/or to the poor packing of homochiral ephedrinium salicylate molecules in the crystal lattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018945401484
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  • 11
    Electronic Resource
    Electronic Resource
    Tris(pyrazol-1-yl)-s-triazine (TPT): X-ray crystallographic, computational, and gas-phase electron diffraction studies (1994)
    Springer
    Structural chemistry 5 (1994), S. 255-264 
    Details
    ISSN: 1572-9001
    Keywords: tris(pyrazol-1-yl)-s-triazine ; crystal structure ; electron diffraction ; AM1 semiempirical calculation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformation of the TPT molecule has been analyzed using experimental and computational techniques. The solid-state molecular structure shows similar conformational features to those in the 2-pyrimidine and phenyl derivatives although a different pattern of bond angles in the triazine ring was observed. The AM1 calculations predicted two conformations of comparable stability (ΔE=1.8 kcal/mol) differing in the orientation of one pyrazole ring. While the minimum energy conformation corresponds to a model displayingC 3h symmetry (φ 1=φ 2=φ 3=0°), the other minimum (φ 1=φ 2=0°,φ 3=180°) is close to that observed in the solid state. The electron diffraction results are consistent with a planar or nearly planar conformation in agreement with the preceding studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275498
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  • 12
    Electronic Resource
    Electronic Resource
    Preparation and characterization of some metal(II) complexes of isocinchomeronic acid and X-ray crystal structure ofcis-diaquabis(hydrogen isocinchomeronato)manganese(II) (1994)
    Springer
    Structural chemistry 5 (1994), S. 165-170 
    Details
    ISSN: 1572-9001
    Keywords: Isocinchomeronic acid ; 2,5-pyridinedicarboxylic acid ; hydrogen isocinchomeronate ; manganese(II) complex ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reactions between Mn(II), Co(II), Ni(II), and Zn(II) ions with isocinchomeronic acid (H2-isocin) afforded complexes of the general formula M(H-isocin)2-2H2O, whereas Fe(II) gives both red and deep red-brown products of the same formula. Various physical measurements suggest that the complexes of M = Co, Ni, Zn, and Fe (brown) are octahedrally coordinated by two aqua ligands and twotrans-N,O-bidentate H-isocin− anions with dimeric hydrogen bonding. Those for M = Mn and Fe (red) are the correspondingcis isomers. The structure of the manganese complex as determined by X-ray crystallography exhibitsC 2 molecular symmetry with Mn-N = 2.279(2), Mn-O(H-isocin)− = 2.196(2), and Mn-O(aqua) = 2.137(2) Å. Each aqua ligand forms two donor O-H ⋯ O hydrogen bonds with carboxy groups of different molecules in adjacent chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02262837
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  • 13
    Electronic Resource
    Electronic Resource
    Synthesis, structure and IR characterization of disodium tetra(9,10-dihydro-9-oxo-10-acridineacetato)zincate(II) bis(ethanol) heptahydrate (1994)
    Springer
    Journal of chemical crystallography 24 (1994), S. 731-737 
    Details
    ISSN: 1572-8854
    Keywords: Synthesis ; crystal structure ; IR data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The synthesis, crystal structure and IR data are reported for Na2[Zn(CMA)4]·2EtOH·7H2O, where CMA− is the 9,10-dihydro-9-oxo-10-acridinacetate ion. The complex crystallizes in the monoclinic space group P2/n, with cell dimensionsa=17.335(9),b=8.440(5),c=21.875(12) Å, β=91.94(5)°,Z=2. The structure was solved by direct methods and refined to a finalR value of 0.0363 for 3022 non-zero reflections. The Zn2+ ion occupies twofold axis and is coordinated to four carboxylate ligands, the ZnO4 tetrahedron is considerably distorted with Zn−O distances of 1.978(3) and 1.961(3)Å. Each Na+ cation interacts with two water, one ethanol, and three carboxylate O atoms comprising distorted octahedron. The Zn2+ and Na+ cations are linked through monooxygen and syn-syn carboxylate bridges forming a trinuclear, mixed-metal cluster. The Zn...Na separation is 3.267(2)Å and Na...Na distance equals 3.520(2)Å. All oxygen bonded H-atoms are utilized in hydrogen bonds. The acridone rings overlap in the crystal with the 3.5 Å interlayer separations. The compound has been characterized by IR spectroscopy.
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    URL: http://dx.doi.org/10.1007/BF01666961
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  • 14
    Electronic Resource
    Electronic Resource
    The synthesis and structural analysis of the new high nuclearity platinum-ruthenium cluster complex Pt2Ru8(CO)18(μ3−EtC2Et)2(μ4−EtC2Et) containing three alkyne ligands (1994)
    Springer
    Journal of cluster science 5 (1994), S. 551-564 
    Details
    ISSN: 1572-8862
    Keywords: Mixed metal ; platinum ; ruthenium ; alkyne ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstarct The ten metal cluster complex Pt2Ru8(CO)23(µ3−H)2, 1 was found to react with EtC2Et to form a new ten metal tris-alkyne complex Pt2Ru8(CO)18(µ3−EtC2Et)2 (µ4−EtC2Et),2 in 35% yield. Complex 2 was characterized by IR,1H NMR , and single crystalx-ray diffraction analyses. The cluster can be viewed as a dodecahedron of eight metal atoms capped with two ruthenium carbonyl groups, two triply bridging EtC2Et ligands and one quadruply bridging EtC2Et ligand. Application of the standard electron counting procedures indicate that this is an unusual complex in which the 18 electron rule applies and the polyhedral skeletal electron pair theory does not. Crystal Data for 2 2.0.5 CH2CI2: space group = P21,a = 12.759(2) A,b=18.438(2)Å,c = 20.197(3) Å,β = 91.59(1)°, Z. = 4, 6394 reflections,R = 0.037.
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    URL: http://dx.doi.org/10.1007/BF01171385
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  • 15
    Electronic Resource
    Electronic Resource
    12-Membered crown ethers. Lipophilic derivatives of benzo- and naphtho-12-crown-4 and their membrane electrode properties. Crystal structures of benzo-12-crown-4 NaI and KI complexes (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 20 (1994), S. 335-351 
    Details
    ISSN: 1573-1111
    Keywords: 12-Membered crown ethers ; ion-selective membrane electrodes ; complexes ; crystal structure ; X-ray analysis ; conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Lipophilic derivatives of benzo-12-crown-4 and naphtho-12-crown-4 have been synthesized. The behavior of the parent compounds and their derivatives in membrane ion-selective electrodes have been studied. Selectivity changes have been observed with the rise in lipophilicity. Crystal structures of the NaI and KI complexes of benzo-12-crown-4 (1 and2) have been determined by X-ray analysis. The alkali metal and iodide ions are in direct contact in2 but not in1. Compound1 [Na(benzo-12-crown-4)2]·I is triclinic, witha=13.368(8),b=10.727(7),c=10.325(4) Å; α=73.56(4),β=77.73(4), γ=108.70(5)°;Z=2, space group is $$P\bar 1$$ . Compound2 [K(benzo-12-crown-4)2·I] is monoclinic, witha=15.807(8),b=12.043(4),c=15.601(6) Å,β=117.74(3)°;Z=4, space groupC2/c. In both compounds the cations interact with all oxygen atoms of two crown ether molecules. Correlation of the crystal structures and behavior of the crown ethers in ion-selective membrane electrodes is discussed.
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    URL: http://dx.doi.org/10.1007/BF00708878
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  • 16
    Electronic Resource
    Electronic Resource
    Dicyclohexylamides as ionophores for li-selective electrodes. Crystal structures of a triamide ligand and its complex with lithium ion (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 20 (1994), S. 53-71 
    Details
    ISSN: 1573-1111
    Keywords: Lithium ionophores ; podand ; dicyclohexylamides ; Li-complex ; crystal structure ; X-ray analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of structure and lipophilicity of dicyclohexylamides on the lithium selectivity in membrane electrodes is discussed. The crystal structures of the triamide podand1 and its complex with LiBr1b has been determined by X-ray analysis. Crystal data for ligand1: C48H83O6N3, triclinic,P1,a=10.749(2),b=12.097(3),c=19.123(6)Å, α=95.76(2),β=80.06(2), γ=100.27(2)0,V=2403(1) Ã3,Z=2. Crystal data for the lithium complex1b: C48H83O6N3·LiBr·x C2H5OH, monoclinic,P2 1/c,a=21.297(6),b=16.316(8),c=19.450(4) Å,β=110.87(2)0,V=6315(3) Å3,Z=4. In the complex the ligand adopts a conformation in which oxygen binding sites surrounding the Li+ cation form a slightly distorted trigonal prism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00707612
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  • 17
    Electronic Resource
    Electronic Resource
    Phase and X-ray study of clathrate formation in the tetraisoamylammonium fluoride-water system (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 17 (1994), S. 137-148 
    Details
    ISSN: 1573-1111
    Keywords: Clathrate hydrate ; phase diagram ; crystal structure ; tetraisoamylammonium fluoride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The phase diagram of the binary (i-C5H11)4NF-water system has been studied in the clathrate formation region. Three polyhydrates have been discovered, two of which (1∶38.9 and 1∶32.7) are the known orthorhombic and tetragonal phases:Pbmn,a=11.88,b=21.53,c=12.70 Å,ρ means=1.019 g cm-3 (0°C), m.p.=32.4°C andP42/m, a=23.729,c=12.466 Å,ρ means=1.062 g cm-3, (0°C), m.p.=31.2°C, respectively. A single crystal X-ray analysis of the novel clathrate hydrate (i-C5H11)4NF·27 H2O is reported. This new clathrate hydrate is tetragonal,I4I/a, witha=16.894(5),c=17.111(2) Å,Z=4, (−50°C), and m.p.=34.6°C. Each (i-C5H11)4N+ cation occupies a four-chamber cavity built of 15-hedra 71635942 (idealized description), with small vacant 5444 cavities filling the intervening space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00711854
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  • 18
    Electronic Resource
    Electronic Resource
    X-ray structure and thermal analysis of a 1∶1 complex between sulfathiazole andβ-cyclodextrin (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 17 (1994), S. 187-201 
    Details
    ISSN: 1573-1111
    Keywords: β-Cyclodextrin ; sulfathiazole ; inclusion complex ; crystal structure ; thermal analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An inclusion complex with the formula (β-cyclodextrin) (sulfathiazole) 8.3 H2O has been crystallized and characterized by physicochemical methods including single crystal X-ray analysis. The complex crystallizes in the monoclinic system, space group P21, witha=15.264(4),b= 16.500(6),c=15.559(5) Å,β=117.29(3)o andZ=2. The structure was solved using published co-ordinates forβ-cyclodextrin in an isomorphous complex. Refinement by block-diagonal leastsquares yieldedR=0.061 for 4706 unique observed reflections. Inclusion of sulfathiazole produces a slight ellipticity in the host conformation, but the guest adopts a conformation similar to that observed in its polymorphs. The guest is held in the macrocyclic cavity predominantly by hydrophobic forces, with the phenyl ring near the host primary hydroxyl side and the thiazole ring near the secondary hydroxyl side. The complex packs in layers parallel to theac-plane. Layers are linked by hydrogen bonding to water molecules which are located outside the cyclodextrin cavity. An extensive network of hydrogen bonds mediated chiefly by water molecules stabilizes the crystal structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00711858
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  • 19
    Electronic Resource
    Electronic Resource
    Inclusion complexes of the natural product gossypol. Recognition by gossypol of halogeno methanes. Structure of the dichloromethane complex of gossypol and single crystal conservation after decomposition (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 17 (1994), S. 317-324 
    Details
    ISSN: 1573-1111
    Keywords: Gossypol ; complex ; crystal structure ; single crystal ; desolvation ; polymorph
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The structures of gossypol complexes are extremely sensitive to the halogenomethane present as the guest; e.g. changing the number of Cl atoms in chloromethane derivatives changes the structure of the gossypol complex. The crystals of C30H30O8·CH2Cl2 are monoclinic, space groupC2/c,a=21.320(4),b=19.199(6),c=15.765(2)Å, β=113.05(2)o,V=5916(2)Å3,Z=8,D x=1.35 g/cm3,T=295 K. The structure has been solved by direct methods and refined to the finalR value of 0.084 for 1828 reflections. In the structure H-bonded gossypol molecules form columns, generating channels in the structure which are filled by guest molecules. After decomposition (desolvation) monocrystals of the complexes are conserved without destruction, in which there are rather wide and empty channels though slightly smaller than in the complex. An attempt is made to explain some peculiarities of the behavior of the gossypol polymorph formed on the basis of its structure with empty channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00707127
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  • 20
    Electronic Resource
    Electronic Resource
    Crystal structure of the product of a condensation reaction of (±)-gossypol with (R)-(+)-1-phenylethylamine. Why do diastereoisomeric diaminogossypols cocrystallize? (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 17 (1994), S. 365-376 
    Details
    ISSN: 1573-1111
    Keywords: Gossypol ; inclusion compounds ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The crystal structure of a compound obtained in a condensation reaction of (±)-gossypol with (R)-(+)-phenylethylamine has been determined by X-ray structure analysis. The crystals of C46H48O6N2·(C4H8O2)2 are monoclinic, space groupP21,a=21.243(3),b=8.666(1),c=28.651(4) Å, β=108.24(1)0,V=5009(3) β3,Z=4,D x=1.195 g cm−3, μ(CuK α)=0.66 mm−1,T=292 K. The structure has been solved by direct methods and refined to the finalR value of 0.091 for 4290 observed reflections and 1049 parameters. There are two diastereoisomeric molecules of the host and four solvent molecules in the asymmetric unit. The host molecules are H-bonded into chains with diastereoisomeric molecules alternating along the chain. The fact that the host prefers the association mode in which molecules with a different configuration of the 2,2′-binaphthyl moiety are H-bonded explains why separation of diastereoisomeric diaminogossypols by fractional crystallization has been unsuccessful. The 1,4-dioxane molecules are accommodated in infinite channels but only every second guest molecule in a channel is H-bonded to the host.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00707132
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  • 21
    Electronic Resource
    Electronic Resource
    A structural two-ring version of a tubular stack ofβ-rings in crystals of a cyclic D,L-hexapeptide (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 18 (1994), S. 27-36 
    Details
    ISSN: 1573-1111
    Keywords: D,L-hexapeptide ; cyclic ; crystal structure ; stacks ; tubular ; β-rings ; channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An X-ray analysis of single crystals (from MeOH) of cyclo(-D-Leu-L-MeLeu-D-Leu-L-MeLeu-D-Leu-L-MeLeu-) has been carried out. The analysis reveals that the molecules of the cyclopeptide occur in the crystals with two slightly different, almost hexagonal backbone conformations of the β-type, and that pairs of molecules with the same conformation interact through their nonmethylated face, forming dimeric units (units A and B) with six interannular H-bonds. This kind of pairing reproduces well that expected for a two-ring element in a stack of antiparalleβ-rings. The X-ray analysis has also revealed the presence in the A units of two water molecules, each at one of two equivalent sites located on the 3-fold axis of the units and equidistant from the center of gravity, and the presence in the B units of one water molecule at the center of the units. This provides experimental support for the idea that stacks ofβ-rings can serve as molecular channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00706936
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  • 22
    Electronic Resource
    Electronic Resource
    N(nPr)4[B5O6(OH)4][B(OH)3]2 and N(nBu)4[B5O6(OH)4][B(OH)3]2: Clathrates with a diamondoid arrangement of hydrogen-bonded pentaborate anions (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 18 (1994), S. 161-175 
    Details
    ISSN: 1573-1111
    Keywords: Pentaborate ; boric acid ; clathrate ; diamond-related network ; hydrogen bonding ; tetrapropy-lammonium ; tetrabutylammonium ; crystal structure ; 11B MAS NMR ; 13C MAS NMR ; thermogravimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Single-crystal X-ray structure analyses of N(nPr)4[B5O6(OH)4][B(OH)3]2,1, and N(nBu)4 [B5O6(OH)4][B(OH)3]2,2, reveal that these materials are novel clathrates, the isotypic host structures of which are three-dimensional assemblies of hydrogen-bonded [B5O6(OH)4]− ionsand B(OH)3 molecules. The assembly of only the pentaborate anions is a distorted (i.e., along [102] elongated) fourconnected diamond-related network. The N(nPr) 4 + and N(nBu) 4 + ions are trapped within the complex three-dimensional channel systems of the host frameworks. Both1 and2 crystallize monoclinically with space groupP21/c andZ=4. The cell constants are:1:a=13.592(5),b=12.082(2),c=17.355(6) Å, β=106.60(2)° (298K);2:a=13.874(3),b=12.585(1),c=17.588(4) Å, β=107.04(1)° (238 K). The results obtained by both11B and13C MAS NMR spectroscopy are discussed. Thermogravimetric studies under a flowing inert-gas atmosphere suggest that water, stemming from polycondensation of the hydrous borate species, is released from the clathrates at ca. 443 K (1) and 398 K (2) before the decomposition of the organic cations starts at ca. 603 K (1) and 603 K (2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00705819
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  • 23
    Electronic Resource
    Electronic Resource
    X-ray crystallographic studies of tricarbonylchromium complexes of calix[4]arene conformers: On an unusual conformation which appears in cone conformers (1994)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 19 (1994), S. 227-236 
    Details
    ISSN: 1573-1111
    Keywords: Calixarenes ; arenetricarbonylchromium ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The structures of three arene-tricarbonylchromium complexes prepared from cone and 1,3-alternate-25, 26,27,28-tetrapropoxycalix[4]arene(1) and Cr(CO)6 were determined by single crystal X-ray studies. Crystal data for 1,3-alternate-1·Cr(CO)3 are space groupP21/a,a=19.496(3)Å,b=11.118(2)Å,c=19.121(2)Å, β=109.95°(1) andV=3895Å3. The structure was refined toRw=0.068. Crystal data for cone-1·Cr(CO)3 are space groupP21/a,a=21.457(4)Å,b=12.184(1)Å,c=14.816(2)Å, β=91.61°(1) andV=3872Å3. The structure was refined toRw=0.077. Crystal data for cone-1·2Cr(CO)3 are space groupP21/a,a=18.019(3)Å,b=41.347(4)Å,c=11.743(2)Å, β=97.39°(1) andV=8676Å3. The single crystal included two similar but slightly different structures but the data were successfully refined toRw=0.092. The structure of 1,3-alternate-1·Cr(CO)3 differs only slightly from that of the regular 1,3-alternate calix[4]arene. In contrast, cone-1·Cr(CO)3 and cone-1·2Cr(CO)3 show an unusual conformation with a pair of faced gablelike roofs, which is considerbly distorted from the regular cone calix[4]arene. The origin of this distortion is discussed in combination with the spectral studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708984
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  • 24
    Electronic Resource
    Electronic Resource
    Structure of trichosanthin at 1.88 Å resolution (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 4-13 
    Details
    ISSN: 0887-3585
    Keywords: trichosanthin ; ribosome-inactivating proteins ; crystal structure ; orthorhombic ; molecular replacement ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Trichosanthin (TCS) is one of the single chain ribosome-inactivating proteins (RIPs). The crystals of the orthorhombic form of trichosanthin have been obtained from a citrate buffer (pH 5.4) with KC1 as the precipitant. The crystal belongs to the space group P212121 with a = 38.31, b = 76.22, c = 79.21 Å. The structure was solved by molecular replacement method and refined using the programs XPLOR and PROLSQ to an R-factor of 0.191 for the reflections within the 6-1.88 Å resolution range. The bond length and bond angle in the protein molecule have root-mean-square deviations from ideal value of 0.013 Å and 3.3°, respectively. The refined model includes 247 residues and 197 water molecules. The TCS molecule consists of two structural domains. The large domain contains six α-helices, a six stranded sheet, and an antiparallel β-sheet. The small domain has a largest α-helix, which shows a distinct bend. The possible active site of the molecule located on the cleft between two domains was proposed. In the active site Arg-163 and Glu-160, Glu-189 and Arg-122 form two ion pairs, Glu-189 and Gln-156 are hydrogen bonded to each other. Three water molecules are bonded to the residues in the active site region. The structures of TCS molecule and ricin A-chain (RTA) superimpose quite well, showing that the structures of the two protein molecules are homologous. Comparison of the structures of the TCS molecule in this orthorhombic crystal with that in the monoclinic crystal indicates that there are no essential differences of the structures between the two protein crystals. © 1994 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340190103
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  • 25
    Electronic Resource
    Electronic Resource
    Cold adaption of enzymes: Structural comparison between salmon and bovine trypsins (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 149-166 
    Details
    ISSN: 0887-3585
    Keywords: crystal structure ; cold adaption ; catalytic efficiency ; protein stability ; anionic ; ectotherm ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The crystal structure of an anionic form of salmon trypsin has been determined at 1.82 Å resolution. We report the first structure of a trypsin from a phoikilothermic organism in a detailed comparison to mammalian trypsins in order to look for structural rationalizations for the cold-adaption features of salmon trypsin. This form of salmon trypsin (T II) comprises 222 residues, and is homologous to bovine trypsin (BT) in about 65% of the primary structure. The tertiary structures are similar, with an overall displacement in main chain atomic positions between salmon trypsin and various crystal structures of bovine trypsin of about 0.8 Å. Intramolecular hydrogen bonds and hydrophobic interactions are compared and discussed in order to estimate possible differences in molecular flexibility which might explain the higher catalytic efficiency and lower thermostability of salmon trypsin compared to bovine trypsin. No overall differences in intramolecular interactions are detected between the two structures, but there are differences in certain regions of the structures which may explain some of the observed differences in physical properties. The distribution of charged residues is different in the two trypsins, and the impact this might have on substrate affinity has been discussed. © 1994 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340200205
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  • 26
    Electronic Resource
    Electronic Resource
    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070101
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  • 27
    Electronic Resource
    Electronic Resource
    Semi-empirical calculations on heterocumulene-heterodiene cycloaddition reactions: Ketene + 1-azabutadiene (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 1-8 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Semi-empirical (AM1) calculations on the 12 isomeric products and the corresponding transition states of ketene-1-azabutadiene [4 + 2] and [2 + 2] cycloaddition reactions as a model system for the reaction of ketenes with 4-iminobenzylfuran-2,3-diones are presented. A [4 + 2] type of reaction of the ketene C=C double bond leading to a six-membered lactam compound is found to be highly favoured both thermodynamically and kinetically. [2 + 2] Cycloadducts generally have significantly higher activation energies. Reactions involving the formation of a carbon-nitrogen bond proceed in most cases via attack of the nitrogen lone pair leading to a zwitterionic intermediate. Depending on the respective cycloadduct, both two-step and concerted, albeit asynchronous, processes were obtained. Based on the structures of the various transition states, some predictions with respect to substituent effects are made. Similarities to and differences from the analogous reaction of ketenimines with oxa-1,3-dienes are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070102
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  • 28
    Electronic Resource
    Electronic Resource
    N-alkylation and N-arylation of anilines starting from a mild N—Mg reagent: Its activation causing the ‘N=C’ coupling to extend the unified structure-reactivity relationshipAryliminodimagnesium reagents, part XXIV. For part XXIII, see ref. 3b. (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 9-17 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: New N-alkylation and N-arylation procedures starting from anilinomagnesium (ArNHMgBr) are reported. For N-alkylation with alkyl bromides, addition of hexamethylphosphoramide to an ArNHMgBr solution in tetrahydrofuran (THF) is effective. After heating at 55°C, N-monoalkylation product was obtained in 60-90% yield, slight dialkylation taking place. The combined use of aryliminodimagnesium [ArN(MgBr)2] with α,ω-dibromoalkanes led to N-arylazacycloalkanes. For N-arylation with iodobenzene, replacement of THF with pyridine and additional use of copper(I) iodide are effective. After heating at 115°C with iodobenzene, mono- and diarylation products were obtained, the former being predominant. The combined use of ArNHMgBr and N,N,N′,N′-tetramethylethylenediamine as the ligand of copper species is effective for elimination of diarylation and other undesired products, and leads to diarylamines in excellent yield. The method is of advantage over the conventional Ullmann and Chapman methods. The polar solvents and copper salt are effective additives for inducing ‘inert combinations’ of ArNHMgBr or ArN(MgBr)2 with alkyl and aryl halides into N—C coupling, to extend the unified view proposed for the reactivity of magnesium reagents. The difference in the roles of N—Mg and N—Cu species is discussed.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070103
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  • 29
    Electronic Resource
    Electronic Resource
    Exploratory photochemistry of alkylbromo- and alkylfluorodiazirines. Excited-state hydrogen migration and carbene formation (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 24-27 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Laser flash photolysis of a series of alklylbromo- and alkylfluorodiazirines in pentane at ambient temperature generates alkylhalocarbenes by decomposition of the diazirine excited states. The halocarbenes can be intercepted with pyridine to form ylides. The ylides absorb intensely between 350 and 400 nm and are fairly long lived (τ » 10 μs), making them convenient probes of the yield and dynamics of the carbene. The yield of the ylides increases with increasing pyridine concentration up to 1·5 M. At pyridine concentrations 〉 1·5 M the yield of ylide is saturated, signifying that every carbene generated in a laser pulse is captured by pyridine prior to reaction with solvent or intramolecular rearrangement. The yield of trappable carbene generated from alkylbromodiazirines closely tracks the bond dissociation energy of the C—H bond adjacent to the diazirine moiety. The data indicate that the excited states of the alkylbromodiazirines suffer C—H migration (or C—C migration with cyclobutylbromodiazirine) and nitrogen extrusion in competition with carbene formation. The yield of trappable carbene derived from the alkylfluorodiazirines is independent of the bond dissociation energy of the adjacent C—H bond. This is probably a consequence of the great thermodynamic stability of α-fluorocarbenes.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070105
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  • 30
    Electronic Resource
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    Low temperature enol-enol association of stable 2,2-diarylethenolsstable simple enols, part 34. For part 33, see ref. 1. (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 28-30 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The low temperature 1H NMR spectra of 2,2-bis(3,5-dibromomesityl)ethenol in CS2-CD2Cl2 (3:7) display new signals which indicate the presence of four enol species whose OH is hydrogen bonded. Oligomerization to intermolecularly hydrogen-bonded enol dimers or tetramers is suggested.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070106
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  • 31
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    Cooperation of aryliminodimagnesium molecules: Deoxygenation of azoxyarenes by mono- and bifunctional reagents in comparison with that by phosphorus(III) reagentsAryliminodimagnesium Reagents: Part XXV. For Part XXIV, see K. Matsuo, Y. Shichida, H. Nishida, S. Nakata and M. Okubo, J. Phys. Org. Chem., 7, 9-17. (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 18-23 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reaction of aryliminodimagnesium [ArN(MgBr)2, IDMg] with nitrobenzene (Ar1NO2) in tetrahydrofuran (THF) gives unsymmetrical (unsym) azoxybenzene, which is deoxygenated to give unsym-azobenzene. The reaction is utilized for the independent preparation of ONN and NNO isomers of unsym-azoxy compounds. The effects of the relative value of the difference between oxidation and reduction potentials of para-substituted reactants, special effects of ortho-substituents of the substrate and also effects of structure and concentration of mono- and bis-IDMg reagents were studied previously, and ‘cooperation of their aggregate excess needed for product formation’ was proposed. This unfamiliar concept for reactions of magnesium reagents was studied further. Supporting evidence was obtained from the retarding effect of trimethylene chains of nitro [3.3] metacyclophanes and the derived azoxy [3.3] metacyclophanes and also from the effect of the length of bis-IDMg's central α,ω-polymethylenedioxy chain appropriate for azoxy deoxygenation. By comparison with deoxygenation by X3P reagents (X = EtO, Me2N), the general needs of cooperation of excess magnesium reagents were confirmed and its role in their reactions is discussed.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070104
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  • 32
    Electronic Resource
    Electronic Resource
    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070201
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  • 33
    Electronic Resource
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    Variation of ρx(ρnuc) with the extent of bond making in SN2 transition states (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 50-53 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The magnitude ρx(ρnuc) is shown to decrease with increase in the extent of bond making estimated by the kinetic isotope effect for the reactions of Y-benzoyl chlorides with anilines, XC6H4NH2, in acetonitrile at 25·0°C.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070109
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  • 34
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    Intramolecular fluorescence quenching and exciplex formation in ω-(1-pyrenyl)alkyl para-substituted benzoates (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 31-42 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Measurements of absorption and emission spectra, fluorescence quantum yields (Φf) and lifetimes (τf) of ω-(1-pyrenyl)alkyl para-substituted benzoates PnX (X = H, Cl, CF3, CN, NO2, with n = 1-4) were carried out in solvents of various polarity. Intramolecular interaction in the ground state is not observed in any of these compounds. PnCN (n = 2-4) shows an intramolecular exciplex emission in solvents of low to high polarity. The broad, structureless emission at longer wavelength observed in ethyl acetate solution of P1CN is ascribed to an ‘exciplex-type’ emission which does not require actual overlapping of the two chromophores. P2CF3 also shows an exciplex emission in solvents of medium to high polarity. The solvent dependence of both Φf and τf increases as the electron-withdrawing ability of the para-sustituents increases. The relationship between fluorescence quenching by electron transfer and para-substituent of PnX is discussed by means of the free energy for electron transfer, ΔGET, obtained from the oxidation and reduction potentials of pyrene and methyl para-substituted benzoates in acetonitrile, respectively. PnH, with positive ΔGET, does not show a solvent dependence of Φf, except for P1H, in which ca 40% of the fluorescence is quenched in acetonitrile. PnCl, with slightly negative ΔGET, shows more efficient quenching, but does not show exciplex emission. PnCN, PnCF3 and PnNO2 have ΔGET values between -0·36 and -0·65 eV, and their fluorescence is fairly efficiently quenched. The fluorescence of PnCN is concluded to be strongly quenched by intersystem crossing from the singlet exciplex to the locally excited pyrene, and by electron transfer from the pyrene part to the benzoate part. That the formation of a singlet exciplex is necessary for intersystem crossing in bichromophoric compounds containing pyrene is thus clearly illustrated.
    Additional Material: 5 Ill.
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    Magnetic coupling between two phenoxyl radicals attached to the phenyl rings of CIS- and trans-stilbenes (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 43-49 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Magnetic coupling between two sterically protected phenoxyl radicals through the cis- and trans-stilbene chromophores was studied by means of their EPR fine structures. While the zero-field splitting parameters D, which are governed by the magnitude of dipolar coupling, were dependent on the geometrical isomerism, the sign of exchange coupling was independent of it and dictated by the topology of the π-conjugated systems: ferromagnetic in o,m-isomers and antiferromagnetic in m,m'-isomers.
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    URL: http://dx.doi.org/10.1002/poc.610070108
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  • 36
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    Mechanisms of aromatic nucleophilic substitution reactions by amines in solvents of low relative permittivity (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 68-79 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The evidence for the mechanisms proposed for aromatic nucleophilic substitution reactions by primary and secondary amines in aprotic solvents of low relative permittivity is reviewed.
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    URL: http://dx.doi.org/10.1002/poc.610070204
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    Estimation of marcus λ for p-phenylenediamines from the optical spectrum of a dimeric derivative (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 55-62 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The radical cation of N,N′-bis-(4-dimethylaminophenyl)pyridazine (3·+) has a near-IR band with a transition energy of 29·7 ± 0·5 kcal mol-1 (1 kcal = 4·184 kJ) in acetonitrile. This band is assigned to a Hush-type charge-transfer band, and the transition energy to the Marcus λ value for electron transfer. Such a large λ is inconsistent with previous estimates of λ for intermolecular electron transfer between mono-p-phenylenediamines and their radical cations. It agrees well with estimates of λ based on AM1 semi-empirical MO calculations, which gives the enthalpy contribution to λin at about 21 kcal mol-1 for 3·+. It is suggested that the traditional method of estimating λin by summing bond displacements weighted by force constants produces values which are significantly too low for systems such as phenylenediamines, where pyramidalization changes are important. The results suggest that λ for tetramethyl-p-phenylenediamine self-electron transfer (10/·+) has been significantly underestimated, and that this prototype organic electron transfer reaction is not as strongly diabatic as was previously concluded.
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  • 38
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    The influence of solvents on the basicity of dipolar amines (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 63-67 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative basicities of six monosubstituted dipolar trimethylamines (XCH2NMe2) were determined in nine different solvents from potentiometric titration. Solvation effects on basicity variations were analyzed by the solvatochromic parameters (π*, α and β). Non-specific solvation of the substituted dimethylammonium ions is not reflected adequately by the solvent's dipolarity-polarizability constant, π*. A better representation of non-specific interaction between solvents and the monosubstituted dipolar trimethylammonium ions is gained from the product of π* and the solvent dipole moment (μ). For these ions where the dipolar substituents are separated from the reaction center by one methylene unit, there is an interaction between the charge of the ammonium ion and the dipolar substituent. As a result, solvent molecules must not only solvate the dipolar substituents, but must also gain access between the lines of force of the dipolar substituent and the charge. Bulky solvents, such as nitrobenzene, cannot access adequately the region between the dipolar substituents and the reaction center to accomplish similar solvation as less bulky solvents.
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  • 39
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    Kinetic study of the formation and rupture of stable tetrahedral intermediates. C—O, C—N and C—S bond formation (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 80-89 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Measured pseudo-first-order rate constants for intramolecular formation of tetrahedral intermediates from N-2-hydroxyethylphthalimide, N-2-aminoethylphthalimide and N-2-thioethylphthalimide at pH 〉 6 are reported. The reaction is specific and general base catalysed, with β(Brønsted) values 0·44, 0·52 and 0·52 respectively. From a plot of log kb (general base rate constants) vs γ′ [the affinities of EtXH (X = O, NH, S) toward the carbonylic carbon], β′nuc values of 0·01 (with OH- as specific base), 0·25 (with imdidazole as general base) and 0·27 (with HPO42- as general base were obtained). The observed relationships pxy = ϑβ′/ - ϑpKa = -ϑ(Brønsted)/ϑγ′ = 0·03 is supported by the predictions of an energy contour diagram, which, on extrapolation to a non-stable tetrahedral intermediate, predicts a late and slightly protonated transition state for the cleavage process. At pH 〈 3, these intermediates cleave to yield only the corresponding diacylimides. These reactions are general base and acid catalysed with β 〉 0·3 and α 〈 0·1. A fast equilibrium between the intermediate and its N-protonated (amide) form is reached. The general base rupture of the latter is faster than that of the corresponding non-protonated intermediate by a factor of ca 109 - 1010-fold.
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  • 40
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    Single-parameter versus dual-parameter correlation for radical reactions. Addition of bromine atoms to α-methylstyrenes (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 96-104 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A rigorous procedure was developed for measuring the relative rates of addition of bromine atoms to eleven substituted α-methylstyrenes (1-Y, with Y = CF3, NO2, F, CN, Cl, Br, CO2Me, Me, COMe, OMe and SMe). The reaction was run in tetrahydrofuran in the presence of HBr, O2 and dibutyl peroxyoxalate at 30°C. All products were derived from the YC6H4CMeCH2Br adduct radicals, which were immediately intercepted by O2. Correlation analysis of all the data confirmed the proposition that in the absence of measurable steric effects, the relative rates for radical additions can be correlated only by a dual-parameter equation and not by a single-parameter equation. Among various combinations of σ* and σx, the (σJJ* + σmb) combination yields the best correlation.
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    URL: http://dx.doi.org/10.1002/poc.610070207
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  • 41
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    Methyl transfer from MeCo(III)Pc to thiophenoxide (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 90-95 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transfer of the cobalt-bound methyl in MeCo(III)Pc to thiophenoxide ion was studied (H2Pc is the planar macrocyclic phthalocyanine; the cobalt is held in the center in this plane). In dimethylacetamide solution, the reaction is rapid, requiring stopped flow for the kinetics, and yielding MeSPh and Co(I)Pc- in good yield. The kinetics are not simple second order, but instead approach a constant rate at high [PhS-], attributed to the reversible formation of an inert complex with PhS- occupying the vacant octahedral site in MeCo(III)Pc, on the other side of the phthalocyanine plane from the methyl group. The kinetics allow the estimation of the equilibrium constant, K, and the SN2 rate constant, k, which at 25°C have values of ca. 9·4 × 103 l mol-1 and 1·8 × 104 l mol-1, respectively. Although these values are rough, the ratio k/K is firm at 1·91 ± 0·02 s-1; this is the limit of the rate at high [PhS-]. An alternative mechanism, which is entirely consistent with the kinetics, involves a rate-determining homolysis of the Co—S bond of the same complex. The mechanism is not favored because the product yields are high for a radical combination process and alternative chain processes are kinetically unacceptable. Further, the rate constant is about what would be expected from the reactivity of other nucleophiles in SN2 reactions. Further arguments in favor of the SN2 mechanism are presented. This transfer of the methyl group from Co to S is part of the possible analogy to the vitamin B12-promoted methionine synthesis in nature. The other step in the biological, enzymatic process is the transfer of methyl from the nitrogen of N-methyltetrahydrofolate to cobalt. An attempt to model this with the very reactive N-methyl-2,6-dichloropyridinium ion was unsuccessful; the reaction took an entirely different course, presumably initiated by electron transfer, but leading to substantial loss of Cl- from the pyridine. No more than 0.5% methyl transfer took place. This system does mimic well the complete natural enzymatic process.
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    Announcements (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 116-116 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070209
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070301
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    Protonation studies on isomeric tetrafluoro-2,11-dithia[3·3]cyclophanes, tetrafluoro[2·2]metaparacyclophane and their corresponding non-fluorinated analogs. Comparison with fluorinated and non-fluorinated[2·2]cyclophanes: A stable ion and semi-empirical (AM1, PM3) investigation (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 105-115 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Protonation of tetrafluoro-2,11-dithia [3·3]paracyclophane and tetrafluoro-2,11-dithia [3·3]metaparacyclophane in high-acidity super acid media, namely FSO3H.SbF5 (1:1) ‘magic acid’-SO2CIF, gave their corresponding acidic disulfonium ions. Additional ring protonation to give a disulfonium-monoarenium trication was not observed. With the non-fluorinated 2,11-dithia [3·3] cyclophanes, the disulfonium ions can be ring protonated in equilibrium to give a dynamic disulfonium-monoarenium trication. Tetrafluoro [2·2]-metaparacyclophane is monoprotonated at the meta ring and gives a complex mixture of conformational isomers. Multinuclear magnetic resonance data on the cyclophane precursors and their derived cations are compared and analysed. The energies, conformations and charge distributions of the isometric fluorinated and non-fluorinated [2·2] - and dithia [3·3] cyclophanes were calculated by the AM1 and PM3 methods, respectively. In all but one case the cyclophane arenium ions predicted by theory to be energetically most favoured are those observed in solution under stable ion conditions. In agreement with experiment, the instabilities of S,S,C-cyclophane trications are also theoretically predicted.
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  • 45
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    Announcement (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. I 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1002/poc.610070302
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  • 46
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    Kinetics and mechanism of electron-transfer reaction of aquothallium(III) and coordinated thallium(III). Oxidation of metol with thallium(III) in acid perchlorate medium (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 117-121 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of oxidation of metol (N-methyl-p-aminophenol) by thallium(III) have been studied in a perchloric acid medium. This organic compound is employed extensively in photographic work. The stoichiometry of the reaction is represented by: C6H4(OH)NHCH3 + TIIII → C6H4(O)NCH3 + TII + 2H+The kinetics indicate the rate law: \documentclass{article}\pagestyle{empty}\begin{document}$$k' = \frac{{Kk\left[{metal} \right]}}{{1 + K\left[{metal} \right]}}$$\end{document} where k′ is the pseudo-first-order rate constant. The rate constants and thermodynamic parameters for the rate-limiting step have been evaluated.
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    Estimation of ionization constants of azo dyes and related aromatic amines: Environmental implication (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 122-141 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ionization constants for 214 dye molecules were calculated from molecular structures using the chemical reactivity models developed in SPARC (SPARC Performs Automated Reasoning in Chemistry). These models used fundamental chemical structure theory to predict chemical reactivities for a wide range of organic molecules from molecular structure. The energy differences between the protonated state and the unprotonated state for a molecule of interest are factored into mechanistic components including the electrostatic and resonance contributions and any additional contributions to these energy differences. The RMS deviation was found to be less than 0·62 pKa units, which is similar to the experimental error.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070304
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  • 48
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    Estimation of the OH⃛O interaction energy in intramolecular hydrogen bonds: A comparative study (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 142-146 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An empirical formula relating directly H⃛O interatomic distance to H⃛O interaction energy is used to estimate this energy in intramolecular O—H⃛O hydrogen bonds calculated for systems of known precise geometry. The values obtained were correlated with spectroscopic characteristics of the H-bond (Δv for OH bands in IR spectra and NMR chemical shifts, δ, for protons) and CNDO and INDO estimations of H-bond energy. The regressions obtained had good or very good correlation coefficients.
    Additional Material: 7 Ill.
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  • 49
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    Cleavage rates for radiolysis-produced radical anions of naphthylmethyl phenyl ethers and naphthyl benzyl ethers (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 147-152 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cleavage reactions of α- and β-naphthylmethyl phenyl ethers and of α- and β-naphthyl benzyl ethers were studied by pulse radilysis. Transient spectra indicate that reactions occur via electron capture followed by cleavage of the resultant radical anions to give arylmethyl radicals and aryloxide ions. Product studies of extensively irradiated samples are consistent with this scheme and show patterns which are informative for radiation studies in general. The reactions were studied in several solvents. The behavior of transient spectra obtained in acetonitrile for these ethers shows clearly that radical anions of the naphthylmethyl ethers cleave more rapidly than do the radical anions of the naphthyl benzyl ethers.
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  • 50
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    Erratum (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 169-169 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070309
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    Forthcoming Events (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 169-169 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070310
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  • 52
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070401
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  • 53
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    Competition between inter- and intramolecular hydrogen bonding in molecules with donor and acceptor groups. Solvatochromic and thermochromic evidence in n-(nitrophenyl)alkylenediamines (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 162-168 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvent effects on the absorption spectra of N-(p-nitrophenyl)dimethylenediamine (Ia), N-(p-nitrophenyl)trimethylenediamine (Ib), N-(p-nitrophenyl)tetramethylenediamine (Ic). N-methyl-N-(p-nitrophenyl)tetramethylenediamine (II), N-butyl-p-nitroaniline (III) and N-(o-nitrophenyl)trimethylenediamine (IV) were studied at different temperatures. Whereas II, III and IV do not show any variation in their spectra characteristics with changes in temperature, I shows a hypsochromic shift with a hypochromic effect when the temperature is increased. The Kamlet and Taft solvatochromic comparison method was applied. A strong effect of the β parameter on I and III was interpreted as being due to the hydrogen bond donor ability of the H atom in the aromatic amino groups. In I, the β influence increases with increase in temperature. These facts are explained by proposing the formation of intramolecular hydrogen bonds between amine groups in all compounds I, besides the intermolecular interactions between compounds I and the solvent. On the other hand, the values of vo, s and b for Ib are smaller than the corresponding values for Ia and Ic. Since in Ib a six-membered ring may be formed, a more stable bond is expected. Comparative 1H NMR of the aniline hydrogen for I and IV (in non-hydrogen bond acceptor solvents) shows a particular downfield chemical shift for I which suggests hydrogen bond formation. Since this effect is independent of concentration, the hydrogen bond is assumed to be intramolecular, in agreement with solvatochromic and thermochromic studies. These conclusions were corroborated by IR spectroscopy in the solid state and in chloroform solutions.
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  • 54
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    Anionic products of the two-electron reduction of aromatic nitriles in liquid ammoniapart 5 of the series ‘reductive alkylation of arenes.’ for parts 1-4, see refs 1 and 2. (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 153-161 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reduction of 9-cyanoanthracene by two equivalents of potassium in liquid ammonia was shown to yield the 9-cyanoanthracene dianion, whereas 1-naptho- and benzonitrile gave the cyanodihydroaryl anions corresponding to the protonation of nitrile dianions at a position para to the cyano group. The 9-cyanoanthracene dianion underwent the same transformation in the presence of a stronger protonating agent, methanol. According to 13C NMR spectral data of the generated species, the cyano group extracts the negative charge from the π-electronic system: ca 0·20:0·25 e in the case of the 9-cyanoanthracene dianion and ca 0·14:0·17 e in the case of cyanodihydroaryl anions. These estimations and the general NMR pattern of π-charge distribution in all the anionic species under investigation are in accordance with data from quantum molecular orbital calculations at the PM3 and INDO levels, being reflected by the fairly good linear relationships between the changes of ring carbon chemical shifts on going to the anionic species from the respective neutral precursors on the one hand and the calculated π-charges on the other. The para-orienting effect of the cyano group in the protonation of nitrile dianions is discussed in terms of the π-charge distribution in the starting dianion and the tendency to form a most stable cyanodihydroaryl anion isomer.
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    Study of the association of 2-oxoindolines in carbon tetrachloride solutions by IR spectra, dipole moments and average molecular weight measurements (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 171-177 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dipole moments, average molecular weights and IR spectra of 2-oxoidoline (I), 2-oxo-3-methylindoline (II) and 2-oxo-3,3-dimenthylindoline (III) and their N-methyl-substituted analogues were studied in CCl4 solutions at various concentrations. It was shown that the molecules with an N—B bond associate exclusively to cyclic dimers. The values of the association constants (K) were determined by IR spectrometry. Other methods gave too broad intervals of possible K values. The spectroscopic association constants of compounds I-III are very similar, 380, 350 and 370 dm3 mol-1, respectively. The vs(NH) band shift on association is 275 cm-1.
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    URL: http://dx.doi.org/10.1002/poc.610070402
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    The volume profile for a cheletropic reaction (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 178-180 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The volumes of activation and of reaction were measured for the reaction between sulphur dioxide and 2,3-dimethylbuta-1,3-diene to form 3,4-dimethylsulpholene. Values of ΔV and ΔV* are -33 and -35 cm3 mol-1, respectively in accordance with a concerted reaction having a very product-like transition state.
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    Secondary α-deuterium isotpe effect on the hydration of p-nitrobenzaldehyde (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 192-195 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The secondary α-deuterium isotpe effect on the equiliburium constant (KD/KH) for the hydration of p-nitrobenzaldehyde is 1·39 ± 0·05. The Kinetic secondary α-deuterium isotope effect (KD/KH) for the addition of water to p-nitrobenzaldehyde is 1·18 ± 0·07. This result demonstrates that there is extensive carbon-oxygen bond formation in the transition state for addition of water to the carbonyl group of p-nitrobezaldehyde.
    Additional Material: 3 Tab.
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    Cryptate acidity scales. Solvent polarity effect on ion-pair and free ion acidity of organic compounds (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 181-191 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: [2.1.1] Cryptated lithium salts of a wide range of CH-acids were studied spectrophotometrically and conductimetrically in solvents of low polarity. Such salts exist in media of different dielectric constants in the form of cryptand-separated ion pairs which are identical in their spectral and conductance properties with common solvent-separated ion pairs. No formation of higher ionic clusters was observed for the studied ions at concentrations below 10-3 mol-1 even in the benzene. The relative equilibrium acidities in benzene, N-methylmorpholine and tetrahydrofuran for a number of CH-acids are reported. Solvent polarity does not influence the cryptate ion-pair acidity of the investigated compounds. The relative free ion acidities were calculated for some of the studied acids in different solvents by combination of the ion-pair acidity values with the conductimetric data on dissociation constants of the cryptate ion pairs. A linear relationship between the free ion acidity and the reciprocal of the dielectric constant was found. An extrapolation method is suggested for the calculation of gas-phase acidity from the data obtained in solution.
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    Quantitative description of structural effects on melting points of substituted alkanes (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 196-206 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Structural effects on the melting points of substituted alkanes, both branched and unbranched, ranging in length from 1 to 19 carbon atoms, were successfully correlated with a variant of the intermolecular force equation which included a variable capable of accounting for the packing energy contribution of the alkyl group. The final data set had 366 data points. The regression equation obtained accounted for 91·85% of the variance of the data with a standard error of 17·9 K. Twenty-nine data points could not be included in the correlation; nine of these are carboxamides. The contributions of the polar variables are slightly larger than those of the nonpolar variables while the contribution of structural variation in the substituent is greater than that in the alkyl group. It will be necessary to determine appropriate values of the packing parameter if compounds with chains longer than 20 carbon atoms are to be included in the model.
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    Calibration of a semi-empirical procedure for predicting the ground-state spin multiplicities of open-shell molecules. Applications to new systems (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 207-217 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A semi-empirical configuration interaction (CI) algorithm is presented for predicting the ground-state spin multiplicity of open-shell systems. The computed energy gaps ΔE(LS—HS) of model systems, Y-phenyl-X-phenyl-Y, where Y is a nitrene or nitroxide radical and X is an exchange coupling unit, are critically compared with the available experimental data. The current method has attenuated the deficiencies of the earlier algorithm proposed by Lahti and Ichimura and the predictions are qualitatively clearer, facilitating the classification of high- and low-spin topologies for isomeric species. The relative effectiveness of different exchange couplers can be discerned semi-quantitatively, and several new exchange couplers are described. The reasons for the qualitative failure of the earlier algorithm are discussed.
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070501
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    Mechanism of the hydride transfer reaction of leuco crystal violet with cyanomethylene acceptors (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 218-220 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the hydride transfer of Leuco Crystal Violet to form the Crystal Violet, cation, the role of cyanomethylene acceptors was found to be essentially different from that of p-benzoquinones, both previously believed to act as π-acceptors in the same manner.
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    Competition between decarboxylation and isomerization in the C3H5O2+ energy surface. Justification of the experimental results by molecular orbital calculations on the solvated ions (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 221-226 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In constrast with recent molecular orbital calculations on the decarboxylation of O-protonated 2-oxetanone, this experimental work indicates that no decarboxylation of this cation occurs in sulphuric acid solution up to 150°C, but instead a clean isomerization to protonated acrylic acid takes place. Parallel theoretical work shows that the gas-phase model is too crude to account successfully for the experimental facts obtained in acidic media. However, the latter are well reproduced when the effect of the solvent is taken into account. The present findings do not necessarily invalidate the reaction mechanism currently accepted to explain the rate enhancement and change of stereochemistry accompanying the decarboxylation of 3,4-disubstituted 2-oxetanones under acid catalysis.
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    Enolimine and geminaldiamine forms in the reaction of pyridoxal phosphate with ethylenediamine. An electrochemical and spectroscopic contribution (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 227-233 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The enol-keto tautomerism of the Schiff bases formed by pyridoxal 5'-phosphate (PLP) with ethylenediamine (Etd) and ethylamine (Et) was studied by electrochemical and spectrophotometric methods. The spectroscopic results revealed differences between the two reactions, i.e. the enolimine/ketoenamine ratio observed in PLP-Etd mixture is higher than that of PLP-Et. The differences observed in the electroreduction mechanism and stability of the Schiff bases formed provide additional evidence for an unusually high concentration of enolimine in PLP-Etd in buffered aqueous solutions.The results are consistent with a cyclic structure such as that previously proposed by Robitaille et al. [J. Am. Chem. Soc. 111, 3034-3047 (1989)] on the basis of spectroscopic data. Protonation of the terminal amino group of the Etd moiety in the Schiff base involves the formation of the cyclic species. The low basicity of ethylenediamine favours the formation of similar concentrations of the enol and keto tautomers of the Schiff base at neutral pH. This behaviour, also observed in the Schiff base formed by PLP and polylysine, may be involved in coenzyme-protein linkages.
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    Number and structure of solvolysis intermediates. Part 3.For Part 2, see Ref. 1.SN1 solvolysis of 2,2-Dimethyl-1-(p-Methoxyphenyl)Propyl p-Nitrobenzoate: Mechanism of the common ion salt effects arising at the stage of the second ion-pair intermediate (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 234-243 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2,2-Dimethyl-1-(p-methoxyphenyl)propyl p-nitrobenzoate (ROPNB) was subjected to solvolysis in phenol in the presence of tetrabutylammonium [carboxy-13C]-p-nitrobenzoate, in which the ‘common ion rate depression’ was confirmed to arise at the stage of the second ion-pair intermediate (Int-2). The unchanged substrate recovered at 46% reaction contained the isotopically labelled leaving group, indicating the occurrence of common ion exchange to the extent of 41-46%. In the solvolysis of the optically active substrate under identical conditions, the unchanged substrate was recovered with 51·4% racemization and ROPh was produced with slightly (1·56%) retained configuration, similarly to the solvolysis in the absence of the common ion salt. These isotope-tracer and stereochemical outcomes indicate that the common ion exchange in this solvolysis system should be attributable to the retentive nucleophilic attack on Int-2 by the common ion salt via a quadrupole (four-centre ion pair) transition state, accompanying the common ion rate depression, and they suggest that the special salt effect also should proceed by an analogous anion-exchange mechanism to that for the common ion effects.
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    Relative thermodynamic stabilities of the isomeric propenylbenzenes (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 256-258 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative thermodynamic stabilities of 2-propenylbenzene (allylbenzene), and the E and Z forms of 1-propenylbenzene were determined over the temperature range 50-170°C by chemical equilibration in DMSO solution with t-BuOK as catalyst. The values of the thermodynamic parameters ΔG⊖, ΔH⊖ and ΔS⊖ at 298·15 K for each isomerization reaction between the title compounds were evaluated.
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    Electronic structure of the disilenyl radical anionDedicated to Professor O. J. Scherer on the occasion of his 60th birthday. (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 251-255 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: According to quantum chemical calculations, the anion radical of disilene adopts a syn- or anti-pyramidal geometry. The former is not a stable entity on the electronic hypersurface and it decreases further in energy by rotation of the Si-Si bond. Energy optimization of various structural alternatives reveals for the anion radical an Si-Si bond slightly longer than a single bond. The anti geometry prefers a C2h geometry whereas the syn geometry resembles a silylene coupled with a silylene radical anion. The fragmentation of disilene into two silylene units is less exothermic for the neutral species than for the anion (radical), as examined by the ab initio calculations.
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    Conformational properties of disulphide bridges. 2. Rotational potentials of diethyl disulphide (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 259-267 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The conformational properties of diethyl disulphide, a model compound for the disulphide bridges in peptides and proteins, were studied with ab initio methods. Stationary point structures were optimized at the HF/6-31G* level with consideration of electron correlation in subsequent single-point MP2 calculations. The six energy minima were also optimized at the MP2/6-31G* level with calculation of zero-point vibrational frequencies and thermal corrections. Additional single-point MP2 energy calculations employed larger basis sets up to 6-311G(2d, p). With positive disulphide chirality, the global energy minimum is a ‘spiral’ conformation with gauche + C-C-S-S torsion angles. The further stability order for energy minima deviates from previous ab initio results. In particular, the extended trans,trans conformer is subject to a significant relative destabilization on inclusion of electron correlation in the calculations and is only the fifth most stable energy minimum with estimated ab initio ΔH298 = 5·13 kJ mol-1. The results presented are relevant for the discussion of conformational properties for the structurally equivalent disulphide bridges in polypeptides and calculations of relative energies with molecular mechanics methods.
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070601
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    Linear free energy relationships in radical reactions. II.For Part I, see Ref. 21. This paper was presnted at the 6th International Symposium on Organic Free Radicals, Nordwijkerhout, The Netherlands, 23-28 August 1992. hydrogen abstraction from substituted toluenes by Tert-Butyl, Tert-Butoxyl and Tert-Butylperoxyl radicals (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 244-250 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Calculations were carried out to study the validity of σ-scales for hydrogen abstraction from substituted toluenes by tert-butyl, tert-butoxyl and tert-butylperoxyl radicals. Rate constants were compiled and evaluated from the literature for meta- and/or para-substituted toluenes. The substituents were characterized by factored ionic sigmas (σI, σR, σR+), ionic scales (σ, σ+) and various radical sigmas (σσ). The dependence of log k values on these substituent descriptors was investigated using ‘stepwise linear regression’ and ‘all possible regression’ methods. The following predictive equations can be recommended: for tert-butyl radicals, at 321 K: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\log \,k_1 \, = \,1.024\, + \,0.776\,\sigma _1 \, + \,0.653\,\sigma _{\mathop C\limits^. }} \quad {(R\, = \,0.8137)} \end{array}$$\end{document} for tert-butoxyl radicals, at 313 K: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\log k_2 = 5.529 - 0.623\sigma ^ +} \quad {(R = 0.9376)} \end{array}$$\end{document} and for tert-butylperoxyl radicals, at 303 K: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\log k_3 = - 1.410 - 0.810\sigma + 0.337\sigma _{\mathop C\limits^. } } \quad {(R = 0.9628)}\end{array}$$\end{document} The results suggest that there is no unversal radical scale for hydrogen abstraction reactions, that the rate is primarily influenced by polar factors (inductive, resonance) and that only two radical scales (σĊ and σα·) are appropriate, showing a small, yet significant, role of radical stabilization.
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    AB initio and semi-empirical investigation of gas-phase carbon acidity (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 268-271 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acidities of a representative range of carbon acids were calculated by various levels of ab initio theory and by the semi-empirical methods AM1 and PM3 in order to ascertain what level is necessary in order to obtain consistently reliable results. The semi-empirical methods give good agreement with experiment in about a third of the cases, but are significantly, and sometimes seriously, in error for the rest. The 3-21G ab initio method consistently underestimates acidities by a substantial amount. The best results were obtained at the MP2/6-31 + G*//6-31 + G* level. Higher level Møller-Plesset corrections worsened the agreement with experiment.
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    Kinetics and mechanism of the aminolysis of benzoic anhydrides (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 273-279 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nucleophilic substitution reactions of benzoic anhydrides, in which one of the rings is substituted, with anilines were investigated in methanol. The product-formation step coincides with the rate-limiting step so that the two rate constants, kXZ and kXZ, for the competitive reaction pathways can be dissected. The two cross-interaction constants, ρXY and ρXY, especially an unusually large magnitude of the latter, indicate that the reaction proceeds by a frontside SN2 attack on either one of the caronyl carbon with a strong interaction between the nucleophile (X) and the leaving group (Z). The mechanism is also supposed by the trends in the activation parameters.
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    Anomalous polar substituent effect on 15N NMR chemical shifts of Aniline derivatives. Acylanilides and related compounds (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 280-286 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 15N chemical shifts of various m- and p-substituted anilides and related derivatives, ZNHC6H4Y [Z = C6H5CO, CH3CO, CF3CO, CH3SO2, (C6H5O)2PO and H], were correlated with σ- constants. With all series of anilides investigated, the plotted points for the m- and p-substituted derivatives tend to be separated from each other and to lie on two different regression lines. Reinvestigation from this point of view revealed that similar separations occur generally with substituted aniline derivatives. The anomalous polar substituent effect was ascribed to the very large contribution of a resonance effect. In addition, the local π-polarization effect causes a negative slope for the m-substituted series in the case of carboxylic anilides.
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    Water-Catalysed hydrolysis of p-nitrobenzyl cellulose xanthate (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 287-295 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spontaneous hydrolysis of p-nitrobenzyl cellulose xanthate (CelXNB) with a degree of substitution (DS) in the range 2-9 was studied in 10% aqueous ethanol at pH 10, and was followed spectrophotometrically by the appearance of p-nitro-α-toluenethiol, in a continuous-flow system where the reactor was shaken. CelXNB was characterized by solid-state 13C NMR spectra. The reaction occurs through two parallel processes due to two xanthate ester groups with different reactivities. The fast hydrolysis was ascribed to the reaction of the C-2 + C-3 isomers, whereas the slow hydrolysis was due to the C-6 isomer. The percentage of the latter is much higher than C-2 + C-3. The solvent isotope effect of the fast hydrolysis (k′H2O/)k′H2D 11 was 2·22 ± 0·16 and the proton inventory indicated that there is only one proton transfer involved in the transition state, where a second water (or a neighbouring OH group) acts as a general base. The entropy of activation of the fast hydrolysis was only 3·3 ± 0·8 e.u., suggesting that the water molecules involved are highly oriented with respect to the coordinates required to reach the transition state. It is proposed that they form part of the three-dimensional hydrogen-bonded ice-like structure that involves the cellulose matrix.
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    Spectrometry and reactivity of phenalenyl anions (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 296-302 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The aromatic odd-alternant phenalenyl anion and a number of its derivatives were prepared in order to study the perturbation of this conjugated anion by methyl and methoxy groups. The conjugated anions were studied by means of 1H and 13C NMR spectrometry, alkylation experiments and semi-empirical calculations. It was found that a substituent at a charged carbon atom perturbs the entire conjugated system, whereas substituents at inactive (uncharged) carbon atoms have a large effect on the positions ortho to the substituent.
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    Potentiometric evaluation of the ion-selective characteristics of 1,4-bridged cubyl diester crown ethers (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 303-308 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cubane diester crown ethers were tested as ion-selective electrodes in poly(vinyl chloride) (PVC) membranes. The four ionophores studied proved to be good K+ neutral carriers, showing Nernstian and near-Nernstian responses to this ion, in the range 10-4-10-1 M. The fixed interferences method was used to determine relative selectivity coefficients for all the electrodes. The highest selectivity for potassium relative to sodium, lithium, calcium and magnesium ions using potassium tetrakis(p-chlorophenyl)borate (KTpClPB) as a resistance modifier and NPOE as a plasticizer was obtained with the 1,4-cubyl diester-25-crown-7 ether ionophore. The effects of KTpCIPB on membrane selectivity were assessed; its removal was found to increase the selectivity of the four ionophores for potassium relative to cesium, sodium, calcium and magnesium ions with minimal effects on lithium and ammonium ions. The compounds tested exhibited a fast Nernstian response to changes in K+ concentration which was stable to within 〈100 μV h-1.
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    Erratum (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 323-323 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070609
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  • 78
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    Hydride transfer reactions of Michler's hydride with different π-accetors (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 309-315 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydride transfer reactions of 4,4′-bis(dimethylaminophenyl)methane (Michler's hydride) with p-benzoquinones were studied. The rate of formation of Michler's Hydrol Blue was followed spectrophotometrically. The second-order rate constants and the activation parameters were estimated. The formation of a charge-transfer complex was observed at low temperatures. Stable and unstable paramagnetic species formed during the reactions were assigned by ESR spectroscopy. The observed kinetic behaviour and the stoichiometry were in line with those previously obtained for the systems involving Leuco Crystal Violet, Leuco Malachite Green and Leuco Bindschedler's Green. Hence the reaction is considered to proceed according to the so-far accepted multi-step mechanism. However, when tetracyano-p-quinodimethane or tetracyanoethylene was used as a π-acceptor, a comparatively stable radical ion pair was formed as a result of a one-electron transfer, followed by the gradual formation of Michler's Hydrol Blue. The kinetic behaviour and the stoichiometry of the reaction were examined, together with the enhanced kinetic effects of added triethylamine. A modified mechanism for these systems is proposed. The role of cyanomethylenes was found to be essentially different from that of p-benzoquinones, and therefore π-acceptors are divided into two groups of cyanomethylenes and p-benzoquinones.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070607
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  • 79
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    Vinyl ether hydrolysis. 30. Effect of β-carboxy and β-carbomethoxy substitution (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 316-322 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rates of hydrolysis of the vinyl ether functional groups of (Z)- and (E)-β-methoxyacrylic acid and (Z)-and (E)-β-methoxymethacrylic acid and their methyl esters were measured in aqueous perchloric acid solution. Additional rate measurements were also made for one substrate, (Z)-β-methoxymethacrylic acid, in buffer solutions down to pH 7, and a rate profile was constructed. The results show that the β-carboxy and β-carbomethoxy substituents produce strong rate retardations, ranging from 2000- to 25 000-fold, for both Z- and E-isomers in both the acrylic and methacrylic acid series. The rate profile for (Z)-β-methoxymethacrylic acid indicates that ionization of this substrate to the carboxylate ion form rises the rate of hydrolysis by a factor of 240. It is argued that this difference in reactivity of ionized and non-ionized forms of the substrate is due to conjugative and inductive effects of the substituents, rather than β-lactone formation as suggested in an earlier observation of the same phenomenon in a different system.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070608
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  • 80
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    Electronic Resource
    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070701
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  • 81
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    Editorial (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. ii 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070702
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  • 82
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    Newer aspects of electron transfer in electrophilic Aromatic Nitration. Radical pairs as reactive intermediates by time-resolved spectroscopy (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 325-351 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aromatic nitration is effectively carried out by the deliberate irradiation of the charge-transfer absorption band (hvCT) of the transient electron donor-acceptor complex [ArH, NO2Y+], where NO2Y+ represents common nitrating agents. Time-resolved spectroscopy demonstrates that the charge-transfer nitration effected in this way proceeds via an electron-transfer mechanism, in which the collapse of the reactive triad, [ArH+ ·, NO2·, Y] is critical to the formation of the Wheland intermediate. Comparative product analyses of toluene and anisole nitrations together with the ‘non-conventional’ products arising from NO+ catalysis, ipso attack and addition/elimination show that the activation process leading to charge-transfer (photochemical) nitration is indistinguishable from that leading to electrophilic (thermal) aromatic nitration.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070703
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  • 83
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    Stereochemistry and kinetics of methoxide ion substitution in (Z)- and (E)-O-methylbenzohydroximoyl cyanides (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 352-358 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The stereochemistry and kinetics of the methoxide ion substitution reactions (Z)- and (E)-methylbenzohydroximoyl cyanidc [PhC(CN)=NOCH3] were investigated. The reaction of the (Z)-hydroximoyl cyanide with sodium methoxide in DMSO-methanol (9:1) solution at 44·8°C gives a mixture of methyl (Z)-O-methylbenzohydroximate [PhC(OCH3)=NOCH3] and the O-methyloxime of α-ketophenylacetamide PhC(CONH2)=NOCH3. The (E)-hydroximoyl cyanide undergoes methoxide ion-catalyzed isomerization to the E-isomer faster than it undergoes nucleophilic substitution. These observations were interpreted in terms of an addition-elimination mechanism in which the rate-limiting step is elimination of the nucleofuge (AN + DN#).
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610070704
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  • 84
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    Kinetic studies on the aminolysis of 1-(trimethylsilyl)ethyl arenesulphonates in acetonitrile and methanol (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 359-363 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nucleophilic substitution reactions of 1-(trimethylsilyl)ethyl arenesulphonates with anilines and benzylamines in acetonitrile and methanol at 65·0°C were studied. The cross-interaction constants, ρXZ, between substituents in the nucleophile (X) and leaving group (Z) are relatively small (0·10 for XC6H4NH2 in MeCN) but similar to those for other SN2 processes at a secondary carbon atom. This provides further evidence for an approximately constant, loose SN2 transition state at a secondary carbon regardless of the size of the Cα substituent. The transition-state variations with substituents X and Z are in accord with that expected from the positive ρXZ value observed: a stronger nucleophile and/or nucleofuge leads to an earlier transition state, i.e. a lower degree of bond making and breaking.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610070705
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  • 85
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    Orbital-controlled reactions catalysed by zeolites: Electrophilic alkylation of aromatics (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 364-370 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The role of orbital control in product selectivity during electrophilic aromatic alkylation catalysed by zeolites was studied both theoretically and experimentally. In order to discuss this, the alkylation of toluene and m-xylene by methanol was carried out on a series of large-pore zeolites (HY). The changes in the para to ortho ratio observed on changing the framework Si/Al ratio of the zeolites were related to ab initio molecular orbital calculations of the LUMO energy of structurally alike model clusters but containing different tetrahedral cations around the active site. The observed correlation is discussed in terms of the HSAB principle by taking into account the influence of the catalyst composition on the reactivity of the electrophilic reagent.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070706
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  • 86
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    Erratum (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 394-394 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070710
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  • 87
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    Selectivity of nitration reactions of aromatic compounds on zeolites H-Y and H-ZSM-11 (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 385-393 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Substrate and positional selectivity in the nitration reactions of benzene and its derivatives (halobenzenes, toluene and o-xylene) by nitric acid and acyl nitrates supported on zeolites H-Y and H-ZSM-11 were studied. The reaction mechanism and effects governing selectivity of the process are discussed.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070709
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  • 88
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    Polyaniline intercalated into zeolites, zirconium phosphate and zirconium arsenate (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 371-376 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aniline (or aniline hydrochloride) was intercalated into zeolite, zirconium phosphate and zirconium arsenate (proton form and sodium form) and subsequently oxidized to polyaniline (PAN) by ammonium peroxodisulphate. The structure of PAN in the host was studied by electron paramagnetic resonance spectroscopy. PAN in the host gave a free-radical EPR signal at 2·0035-2·0037 for the hydrogen or 2·0047-2·0049 for the sodium form of the host, similarly to the ermeraldine salt (PAN-2S) or emeraldine base (PAN-2A) form of PAN. Saturation occurs in PAN-HZ and PAN-HS. In contrast, the intrachannel PAN in HY was unsaturated under the same conditions. Conduction in PAN-HZ and PAN-HS was predominately carried out by variable-range hopping and tunnelling respectively, and PAN-HY showed insulating properties.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070707
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  • 89
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    Catalytic and computer simulation studies of carbon-sulphur bond cleavage over zeolite-YNCL Communication No. 5768. (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 377-384 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: N-Substituted carbonimidodithioic acid dimethyl esters, when reacted with an active methylene compound such as nitromethane, undergo carbon-carbon bond formation followed by carbon-sulphur bond cleavage in the presence of zeolite catalysts to give 1-substituted amino-1-methylthio-2-nitroethenes. This carbon-sulphur bond cleavage is facilitated by the presence of rare earth cations in the zeolite-Y framework. The shape selectivity of the zeolite also plays an important role in this cleavage reaction. Force field calculations adopted for the molecules involved in the reaction indicate the geometry and conformational flexibility of these molecules. The computer-simulated model for the zeolite-Y is correlated with the conformation and shape of the reactant and product molecules to explain the variation in yields obtained in the conversion of substituted dimethyl esters.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070708
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  • 90
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070801
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  • 91
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    The kinetics and mechanism(S) of nucleophilic attack by catecholate anion on epibromohydrin-d2 (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 395-398 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction which forms hydroxymethylbenzodioxane from epibromohydrin and catecholate anion was examined by ultraviolet spectroscopy for the kinetics and by proton nuclear magnetic resonance spectroscopy to follow the fate of CD2 from reactant to product. Over the practical temperature range it was found that both CH2 positions in the epihalohydrin are attacked by catecholate anion to give product. Therefore, the difference in energy for the two pathways was small. The individual rate constants were obtained from the total rate constants. Further, the individual ΔH
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070802
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  • 92
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    Mechanism of reaction of azobenzene formation from aniline and nitrosobenzene in basic conditions. General base catalysis by hydroxyide ion (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 399-402 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of nitrosobenzene with aniline, to give azobenzene, in basic conditions was studied. It was shown that the reaction exhibits general base catalysis by different buffers giving a Brønsted coefficient β = 0·318. As in previous studies, a two-step process with a first step of attack of aniline on nitrosobenzene to give an addition intermediate and a second step of dehydration of this intermediate is proposed to interpret the mechanism of the reaction. The analysis of the Brønsted relationship and of the intermediate of the reaction led to the suggestion that hydoxide ion catalyses the reaction by a mechanism of general base catalysis in the dehydration step.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070803
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  • 93
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    σ-π and η-π Stabilization energies in vinyl and phenyl compounds (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 403-411 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A means for determining the stabilization energies, Ec(X), resulting from σ-π and n-π interactions in vinyl and phenyl compounds is described. It is based on extensions of the additivity principle for thermochemical data for organic compounds. The results also provide a method for predicting heats of formation of unsaturated compounds from those of (known) saturated analogues. It is shown that there is a linear relationship between the stabilization energies Ec(X) and the Hammett substituent constants σp+(X). The new results have been used to predict the heats of formation of a number of saturated and unsaturated Si-, Ge-, Sn-, P-, As-, Se-, Zn-, Cd- and Hg-containing species.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070804
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  • 94
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    Salt and solvent effects on alkaline hydrolysis of N-hydroxyphthalimide. Kinetic evidence for ion-pair formation (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 412-419 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effects of the concentrations of LiCl, NaCl, KCl, CsCl, Na2CO3 and BaCl2 on the rates of reactions of hydroxide ion with ionized N-hydroxyphthalimide (NHP-) at 30°C and in H2O-MeCN solvents containing 10, 50, 60, 66, 70, 76 and 80% (v/v) MeCN reveal the formation of ion-pair complexes between cations of the salts, which probably exist in solvent-separated loose ion-pair forms (Mn+⃛Xk-) and NHP-. An increase in MeCN content from 2 to 76% (v/v) causes an increase in the association constants (K) by factors of 40, 21 and 9 for LiCl, NaCl and KCl, respectively, while the respective increase in the rate constants (k′s1) for the collapse of the ion-pair complexes to product is ca two-fold. The values of k′s1 remain almost unchanged whereas the values of K increase 7·5-fold with an increase in MeCN content from 2 to 70% (v/v) for CsCl. Ion-pair complex formation was not detected in the presence of Me4NCl at 70% (v/v) MeCN. The observed pseudo-first-order rate constants are highly sensitive to the valence state of cations and almost insensitive to the valence state of the anions of the salts.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070805
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  • 95
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    Molecular mechanics calculations (MM3) on alkyl iodides (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 420-430 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The MM3 force field has been extended to cover alkyl iodides. Structures, vibrational spectra and heats of formation have been well fitted to available experimental data. The experimental and ab initio conformational relationships are also satisfactorily reproduced.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070806
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  • 96
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    Kinetics and mechanism of the imidazole-catalysed hydrolysis of substituted N-benzoylimidazoles (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 431-436 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Imidazole (Imz)-catalysed hydrolysis of benzoate esters proceeds via the intermediate formation of N-benzoylimidazoles. This paper considers the second step of this reaction, viz., Imz-catalysed hydrolysis of N-(4-X-benzoyl)imidazoles, X = CH3, H, Cl, CN and NO2, and N-(disubstituted benzoyl)imidazoles, 2-chloro-4-nitro, 2, 4-dinitro and 3,5-dinitro, in water-acetonitrile mixtures (10% or 14%, v/v, in organic solvent). On the basis of catalytic rate constants and the kinetic solvent isotope effect, it is shown that catalysis by Imz is of the general-base type. Unexpectedly, the hydrolysis of N-(2,4-dinitrobenzoyl)imidazole was found to be slower than that of N-(4-nitrobenzoyl)imidazole. It is shown that this reactivity order is due to a combination of a steric effect and stabilization of the reactant state due to a donor-acceptor interaction between the Imz moiety and the 2,4-dinitrophenyl ring.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610070807
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    Micellar catalysis of organic reactions. Part 35. Kinetic determination of the critical micelle concentration of cationic micelles in the presence of additives (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 437-441 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The critical micelle concentration of solutions of cetyltrimethylammonium bromide and of tetradecyltrimethylammonium bromides were determined by a kinetic method. This involved the determination of the rates of the hydroxydehalogenation of some activated aromatic substrates over a wide range of detergent concentrations. Measurements were made in solutions containing significant quantities of added hydroxyl ion and substrates which were themselves amphiphilic. Conventional methods cannot be applied with confidence to such systems. The effects of changing hydroxyl ion concentrations, added sodium bromide, changing the nature of the aromatic substrate (whether neutral or charged), the identity of the micellar counterion and the temperature were investigated. It was wound that added bromide or hydroxyl ions resulted in a lower CMC whereas increased temperature led to an increase in the CMC. The nature of the micellar counterion (Br, F, OH, SO4) had little effect on the CMC. The presence of a charged aromatic substrate led to a considerable lowering of the CMC, whereas the neutral aromatic substrate used showed very little effect.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070808
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  • 98
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    Micellar catalysis of organic reactions. Part 36. Nucleophilic aromatic substitution reactions in hydroxy functionalized micelles with bulky head groups (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 442-447 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of several nitro activated aromatic halides with hydroxide ions was studied in the presence of hydroxy functionalized micelles containing bulky head groups, e.g. C16H33N+R2CH2CH2OH Br-, where R = Me, Et, Bu. In a biphasic reaction, the aryl halide is first converted into an aryl mincellar ether which subsequently reacts with hydroxide ions to form the phenolic product. Despite the increased nucleophilicity of hydroxide ions as water is squeezed away from the micelle surface by the bulky head groups, no direct reaction of the aromatic substrate with hydroxide ion is detectable. In the second phase of reaction, the breakdown of the aryl micellar ether to form the phenolic product, the order of reactivity in the different micelles is dependent on the steric interactions between substituents ortho to the reaction centre and the head group of the micelle. For compounds having one substituent ortho to the reaction centre, the order of reactivity is Bu 〉 Me 〉 Et, whereas for 2-chloro-1,3-dinitrobenzene, which has two substituents ortho to the reaction centre, the order is Me 〉 Et 〉 Bu.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070809
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  • 99
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    Bimolecular nucleophilic substitution at a resonance-stabilized carbenium ion: Elevated value of cross-interaction constant, imbalanced transition state and the non-interactive phenomenon (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 448-454 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A characteristic feature in the bimolecular nucleophilic substitution reactions at a resonance-stabilized carbenium ion has been shown to be an imbalanced transition state resulting in an elevated value of the cross-interaction constant, which in turn leads to a non-interactive phenomenon. Examples of the reactions of ring-substituted phenylethyl and benzhydryl cations are given.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610070810
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  • 100
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610070901
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