On the representation of molecular quadrupole moments in terms of atomic moments

The magnitude and algebraic sign of the molecular quadrupole moments of the homonuclear diatomic molecules N2, O2, F2, P2, S2 and Cl2 are analyzed by expressing them as a sum of the quadrupole moments of the free atoms and an induced molecular quadrupole due to bond formation. This induced molecular quadrupole is further analyzed in terms of in situ atomic dipole and quadrupole moments constructed following the electron partitioning method suggested by Hirshfeld. These in situ moments are interpreted in terms of the sigma and pi character of the chemical bonds and are compared with those predicted by the DMA method of Stone (The Theory of Intermolecular Forces; Clarendon: Oxford, 1996).     

Selective oxoammonium salt oxidations of alcohols to aldehydes and aldehydes to carboxylic acids

The oxidation of alcohols to aldehydes using stoichiometric 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) in CH(2)Cl(2) at room temperature is a highly selective process favoring reaction at the carbinol center best able to accommodate a positive charge. The oxidation of aldehydes to carboxylic acids by 1 in wet acetonitrile is also selective; the rate of the process correlates with the concentration of aldehyde hydrate. A convenient and high yield method for oxidation of alcohols directly to carboxylic acids has been developed.     

Suspension polymerization of vinyl chloride initiated by in situ generated diisobutyryl peroxide

It was found that diacyl peroxides can be formed in situ in a polymerization medium by the reaction of an acid anhydride with hydrogen peroxide. For the specific application to aqueous vinyl chloride polymerization, an initiator system based on the base-catalyzed reaction of isobutyric anhydride with hydrogen peroxide to produce diisobutyryl peroxide gave very good results. In contrast, the acid chloride was completely ineffective as a peroxide precursor in this reaction. Studies pointing to diisobutyryl peroxide as the initiating species; investigations of reactant stoichiometry; and comparison of the in situ system with preformed diisobutyryl peroxide were conducted. It was shown that this system makes possible the polymerization of vinyl chloride at 30°C at rates comparable to those obtained with dialkyl peroxydicarbonates at 50°C, thus demonstrating the ability of this system to initiate vinyl chloride polymerization at low temperature. The rates of vinyl chloride polymerization with the use of different concentrations of in situ diisobutyryl peroxide at 30, 40, and 50°C were determined. Similarly, polymerization rates with the use of combinations of in situ diisobutyryl peroxide and n-propyl peroxydicarbonate were determined. The data obtained demonstrate rapid initiation of the polymerization reaction and a reduction in polymerization time made possible by this dual initiator system. These results were verified in pilot-plant and commercial-scale PVC polymerizations.     

Catalyzed cross-coupling of allyl bromides with allyl tin reagents

The reaction of allyl bromides with allyl tin reagents, catalyzed by palladium or zinc chloride gives cross-coupled products without allylic transpostion in the allyl halide partner but with predominate allylic rearrangement from the tin partner.     

Amine catalysis in phosphoryl transfer from 2,4-dinitrophenyl phosphate in aprotic and protic solvents

Reactions of tetra-n-butylammonium 2,4-dinitrophenyl hydrogen phosphate, (ArPH)^?(R₄N)⁺, in aprotic and protic solvents, in the absence and in the presence of alcohols or water, ROH, are compared with analogous reactions of the salt in the presence of hindered and unhindered amines, e.g. diisopropylethyl amine and quinuclidine. Similar studies are performed with the acid, ArPH₂, in the presence of variable amounts of amines. The release of phenol and the fate of the phosphorus compounds are followed by ¹H and ³¹P NMR spectrometry. In the absence of free unhindered amine, reactions of the monoanion are relatively slow, sensitive to steric hindrance in the alcohol, and incapable of producing t-butyl phosphate from t-butanol; reactions of the dianion are relatively fast, insensitive to steric hindrance in the alcohol, and produce t-butyl phosphate. In the presence of free unhindered amine, reactions of the monoanion are relatively fast but still sensitive to steric hindrance in the alcohol, and hence do not produce t-butyl phosphate. The intermediate CH(CH₂CH₂)₃⁺NP(O)(OH)O^? is detected in the presence of quinuclidine. Reactions of the dianion in the presence of unhindered amines are analogous to those observed in the presence of hindered amines. The uncatalyzed and the nucleophilic amine-catalyzed reactions of the monoanion are assumed to proceed via oxyphosphorane, P(5), intermediates. The dianion reactions, which are not susceptible to nucleophilic catalysis, are assumed to proceed via the monomeric metaphosphate ion intermediate, PO₃^?. Significant effects related to solvent properties are observed in these reactions.     

The structure of the cations from 2– and 4-pyrimidones

An infrared spectral investigation of a number of pyrimidine and pyrimidone hexachloroantimonates is reported. Typical aromatic absorption bands found in pyrimidinium salts were absent in the pyrimidone cations. 2-And 4-Pyrimidone hexachloroantimonates, as well as their N-methyl- and N,N'-dimethyl derivatives, exhibit intense carbonyl absorption bands between 1720–1729 cm^?1 (solid state) which corroborates N-protonation of pyrimidones.     

The molecular structure of 1,1-dimethyl-3-phenylpyrazolium-5-oxide

The molecular structure of 1,1-dimethyl-3-phenylpyrazolium-5-oxide has been determined by a single crystal x-ray diffraction study. The crystals are monoclinic, space group P2₁/a, with unit cell dimensions a = 12.630 (5) Å, b = 6.644 (1) Å, c = 12.486 (5) Å, β = 99.17 (2)°. The final R value was 0.049 for 2930 reflections. The bond lengths and angles suggest that a significant contribution to the structure is made by a resonance form in which one of the ring bonds does not exist. No close intermolecular approaches were found.     

Apparent molar volumes of crown ether complexes in several solvents at 25°C. An estimation of ionic electrostriction

The apparent molar volumes of equimolar concentrations of 18-crown-6-ether (CE) or dibenzo-18-crown-6-ether (B₂CE) and MCl (M=Na, K, or Cs) or MI in dilute solutions of anhydrous methanol, acetonitrile and dimethylsulfoxide have been calculated from density data measured at 25°C. After extrapolation to infinite dilution these results together with the apparent molar volumes of the crown ethers and the alkali metal halides were used to calculate the limiting partial molar volume change for the formation of the complexes. By noting that the charge of the complexed cation has been shown to be completely shielded from the solvent, the volume of complexation can be assumed to be a good estimation of the volume change due to electrostriction of the solvent by the cationic charge. The results are compared to the predictions of the Hepler equation.Presented at the Symposium on Electrochemistry and Spectroscopy of Solutions, Honoring Johannes Coetzee, University of Pittsburgh, November 30, 1989.On leave from Rhodes University, Grahamstown, South Africa.