Quantum chemical studies on electrophilic addition

The geometries of the 2-chloroethyl and ethylenechloronium cations, two possible intermediates in the electrophilic addition of chlorine to ethylene, have been fully optimized using ab initio molecular orbital calculations employing the split valence shell 4-31G basis set.These geometries were then used to compute more accurate wave functions using Dunning's double-zeta basis set. The bridged chloronium ion was found to be more stable by 9.35 kcal/mole, the opposite order of stability from the C₂H₄F⁺ ions. Interconversion of the two C₂H₄Cl⁺ cations was computed to have a barrier of 6.25 kcal/mole.The activation energy for this chlorination reaction, using the ethylenechloronium cation and a chlorine anion at infinite separation as the model for the activated complex, was computed to be 128.7 kcal/mole, showing that this is not a feasible gas phase reaction.     

An SCF-MO study of the electronic structure of the [LiNH3] cation and related molecules

We examine the effect of the charge and degree of protonation of a ligand on its power as a donor. The following molecules are studied [LiNH₃]⁺, LiNH₂, Li₂NH, and Li₃N, which may to a good approximation be regarded as combinations of Li⁺ ions with the ligands NH₃, NH ₂ ^? , NH^?2, and N^?3.     

Phase-transfer catalysis-3: Acetylation of 2-acylcycloalkanones

With the exception of 2-formylcyclohexanone, which yields the E-exo-enol acetate, the phase-transfer catalysed acetylation of 2-acylcyclohexanones produces the 1-acetoxycyclohexene derivatives as the major products. The 1-acetoxy derivative is also obtained in good yield from the acetylation of 2-methoxycarbonylcyclopentanone but, generally, acetylation of 2-acylcyclopentanones yields the E-exo-enol acetates. 2-Acetylcyclopentanone, however, produces not only the E- and Z-exo-enol acetates, but also the endo-enol acetate, in a ratio of ca 2:2:1. The exo and endo-enol acetates were distinguished by ¹³CNMR spectroscopy and use of LIS reagents confirmed the configurational assignments of the exo-isomers     

Synthetic thermally reversible gel systems. VII

Polymethacrylylglycinamides (PMG), like polyacrylylglycinamides (PAG), form thermally reversible aqueous gels, but higher molecular weights and/or concentrations are required and the melting points of the gels are lower. The heats of crosslinking for aqueous PMG gels fall in the range of ?5 to ?10 kcal/mole of crosslinks, the same as for aqueous PAG gels, implying that the crosslinks are chemically similar. PMG and PAG are incompatible with each other but both are individually compatible with some types of gelatin. The solubilities of PMG and PAG are similar. Various reagents, however, affect PMG and PAG gels in quite different manners. Aqueous PMG solutions, just outside conditions required for gelation, are rheopectic. Intrinsic viscosities [η] of PMG in 2M NaCNS are about 2.5 times those in water. The Huggins' k′ value for PMG in 2M NaCNS has a value of 0.39–0.40, and both it and [η] are essentially temperature-independent over the range 25–45°C. In water at 25°C for PMG, k′ has an average value of about 1.4. With increasing temperature, for H₂O, there is a considerable increase in [η] which is accompanied by a decrease in the value of k′. Osmotic molecular weight measurements on unfractionated PMG in H₂O at 40°C yield π/c versus c plots having essentially zero slope, implying a value of close to zero for the second virial coefficient, a value of about 0.5 for the polymer–solvent interaction parameter, and a condition close to a θ condition. An approximate viscosity–M _n relationship for polydisperse PMG is [η]_{2M NaCNS, 25deg;C} = 1.7 × 10^?8 M _n^1.5. The low value of K and high value of the exponent do not result from large differences in polydispersity but rather from a stiff, rodlike configuration in solution. This steric hindrance to rotation also manifests itself in the extreme brittleness of PMG films and in a ΔH_p for homopolymerization of only ?6 kcal/-mole. The infrared spectra of MG monomer and PMG are recorded as well as the density and refractive index for PMG. PMG has a glass transition at 226°C by DTA and by TGA, thermal decomposition sets in at about 300°C. From copolymerization with acrylic acid, values of 1.66 and +0.06, respectively, were obtained for the resonance factor Q and the electrical factor e for MG monomer.     

The equilibrium shapes of crystals and of cavities in crystals

Surface free energies are assumed to be the sum of the excess free energies of bonding of molecules in or near the surface, and the stable form of a crystal or cavity is assumed to be the form that makes the sum of these excess free energies a minimum. When only plane surfaces are allowed, this model predicts the same shapes for crystals as an equation of Wulff (2. Kristallogr. 34, 449 (1901)), which is based on the macroscopic thermodynamic relation of Gibbs (“The Collected Works, Vol. 1.: Thermodynamics,” Longmans, Green, New York (1931)). The model predicts rounding of edges and corners of kinds which are not allowed by the Wulff relation and predicts that spherical forms of particles and cavities can be stable despite anisotropic surface free energies. The model provides a useful framework for analysis of whether unstable crystal or cavity shapes will evolve into stable or metastable forms. Some crystals and cavities that have been assumed to have equilibrium shapes instead have metastable shapes.     

The reactions of 3-Butyl-1,2-diphenylphosphindole with dimethyl acetylenedicarboxylate

Unlike 1,2,5-triphenylphosphole, 3-butyl-1,2-diphenylphosphindole reacts smoothly with two molecules of dimethyl acetylenedicarboxylate to give the phosphindole oxide, a yellow adduct and a colourless adduct. The case of the reaction is taken to indicate less lone pair interaction with the π-system in phosphindoles than in phospholes. The yellow adduct is shown to be a phosphindolium cyclopentadienylide, i.e. an adduct of the phosphindole and two molecules of the ester less one oxygen atom. The colourless adduct is shown to be a 1:2:1 adduct of the phosphindole, the ester and water and has a benzodihydrophosphonin structure. Mechanisms for the formation of both adducts are proposed. Adducts of this general type were previously unknown in organophosphorus chemistry.     

Donor-stabilized cations and imine transfer from N-silylphosphoranimines

A series of donor-stabilized N-silylphosphoranimine salts [DMAP.PCl2=NSiMe3]+X- (DMAP = 4-(dimethylamino)pyridine) were prepared by the reaction of Cl3P=NSiMe3 with DMAP in the presence of silver salts AgX (X = OSO2CF3, BF4, and SbF6). Repeating the reaction in the absence of AgX gave the chloride salt [DMAP.PCl2=NSiMe3]Cl which has been shown to be in equilibrium with free DMAP and Cl3P=NSiMe3. Attempts to stabilize a N-silylphosphoranimine cation with phosphine donors led to unexpected imine transfer chemistry. For example, Cl3P=NSiMe3 reacts with phosphines, R3P (R = nBu and Ph), to produce the metathesis products PCl3 and R3P=NSiMe3 which subsequently react together to afford the N-phosphinophosphoranimines R3P=N-PCl2 and ClSiMe3 as a byproduct.     

Determination of naphthols by flow-injection chemiluminescence

1-Naphthol, 2-naphthol, 2-naphthol-6-sulphonic acid, 1-amino-2-naphthol-4-sulphonic acid and 1-amino-2-naphthol hydrochloride are determined by the chemiluminescence produced by acidic permanganate oxidation in a flow system. Rhodamine B is used as sensitizer. The limits of detection are ca. 5×10^?7 M in a 20-μ sample.     

Countable Fréchetα 1-spaces may be first countable

It is shown to be consistent that countable, Fréchet, ₁-spaces are first countable. The result is obtained by using a countable support iteration of proper partial orders of length ₂.The research of both authors is partially supported by NSERC     

Stereochemistry of ethynylation of 2,7-dialkyl- and 1,2,7-trialkyl-trans-decahydro-4-quinolones

The effect of the nature of the acetylide, the temperature, and the character of the solvent on the stereochemistry of ethynylation of isomeric 2,7-dialkyl- and 1,2,7-trialkyldecahydro-4-quinolones was investigated. Acetylenic alcohols that have an axially oriented ethynyl grouping were synthesized. Conditions for the stereospecific synthesis of epimeric (with respect to C₄) acetylenlc alcohols were found. The isomers of acetylenic alcohols obtained were incapable of interconversions under the reaction conditions.See [1] for our preliminary communication.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1086–1091, August, 1980.