Effect of ionic additives on the elution of sodium aryl sulfonates in supercritical fluid chromatography

Addition of a small amount of polar solvent (i.e., modifier) to CO2 in packed column supercritical fluid chromatography (SFC) has shown major improvements in both polar analyte solubility and interaction of the polar analyte with the stationary phase. Recently, the addition of an ionic component (i.e., additive) to the primary modifier by one of us has been shown to extend even further the application of SFC to polar analytes. In this work, the effect of various ionic additives on the elution of ionic compounds, such as sodium 4-dodecylbenzene sulfonate and sodium 4-octylbenene sulfonate, has been studied. The additives were lithium acetate, ammonium acetate, tetramethylammonium acetate, tetrabutylammonium acetate, and ammonium chloride dissolved in methanol. Three stationary phases with different degrees of deactivation were considered: conventional cyanopropyl, deltabond cyanopropyl, and bare silica. The effect of additive concentration and additive functionality on analyte retention was investigated. Sodium 4-dodecylbenzene sulfonate was successfully eluted using all the additives with good peak shape under isocratic/isobaric/isothermal conditions. Different additives, however, yielded different retention times and in some cases different peak shapes.     

Copolymerization of styrene. V. Copolymerization with α-cyanocinnamamide

Copolymers of styrene with α-cyanocinnamamide were prepared by free radical initiation in bulk and in DMF solution and also by thermal initiation in bulk. The copolymerization parameters were determined by the conventional scheme of copolymerization and by an improved scheme taking into account the penultimate unit. Different values of the copolymerization parameters were obtained at the above mentioned different polymerization conditions, indicating the existence of a solvent effect. The influence of the comonomer on some of the basic properties, like intrinsic viscosity, solubility, melting range, and glass transition temperature and on some mechanical and behavior properties of the copolymers was studied in comparison with homopolystyrene.     

The reaction of 2-picoline N-Oxide with o-substituled benzoates and lsatoic anhydrides

The reaction of 2-picoline N-Oxide anion with o-substituted henzoates and isatoic anhydrides to give synthetically useful l-(2-methoxyphenyl)-2-(2-pyridinyl)ethanone N-oxides, I-(2-hydroxy-phenyJ)-2-(2-pyridinyl)ethanone N-oxides and I -(2-arninopheny])-2-(2-pyridinyl)ethanone N-oxides is described.     

Characterization of internal salts by laser mass spectrometry

An intermolecular alkyl transfer reaction (ATR) leading to ion-pair formation has been observed for internal salts by using laser mass spectrometry (l.m.s.). Positive- and negative-ion spectra both show evidence for alkyl transfer. Both the LAMMA-500 (transmission) and LAMMA-1000 (reflection) laser mass spectrometers were used. The positive-ion laser mass spectra obtained by these two instruments show some significant differences; no significant differences were observed in the negative-ion spectra. Results obtained for quaternary ammoniohexanoates as a function of laser power indicate that the extent of ATR is greater at high laser power. Addition of a small amount of p-toluenesulfonic acid to the ammoniohexanoates reduces fragmentation and enhances the intensity of the quasimolecular ion (M + H)⁺ relative to ATR. Results from deuterated sultaines were used to confirm intermolecular alkyl transfer and to elucidate some fragmentation processes. Field-desorption (f.d.) mass spectra of internal salts show similarities and differences from l.m.s.; not all internal salts showed the alkyl transfer reaction in f.d. Cluster ion formation was observed in f.d.m.s. but not in l.m.s.     

A statistical thermodynamic supermolecule-continuum study of ion hydration: Cell and shell methods

A theoretical study of ion hydration using the statistical thermodynamic supermolecule-continuum method is described. The cell and shell methods are used for configurational averaging. Enthalpies, free energies and entropies are calculated for Li⁺, Na⁺, K⁺, F^– and Cl^– each four coordinated with water. The results are in reasonable accord with experiment. A comparison of the site method, cell method and shell method results is presented. The supermolecule-continuum approach to solvent effects seems to be capable of accommodating essential features for the calculation of solvation energy and solvent effects on structure and properties.     

Organosilicon compounds : LI. Further studies of the base-catalysed solvolysis of N-(triorganosilyl)anilines

Relative rates of solvolysis of some N-triorganosilylanilines in mixtures of ethanol and aqueous potassium hydroxide have been determined, with results as follows. (i) For XC₆H₄NHSiEt₃ compounds in MeOH (5 vol) + aq. alkali (2 vol) at 50°: (X =) H, 1.0;p-Me, 0.80;p-OMe, 0.83;m-Me, 0.90; o-Me, 0.87; p-SMe, 1.90; p-F, 1.7; p-Cl, 2.8; o-Cl, 14; m-Cl, 4.2; m-NO₂, 18; p-CN, ca. 43; p-NO₂, ca. 120. (ii) For PhNHSi(C₆H₄Y)₃ compounds in MeOH (10 vol) + aq. alkali (1 vol) at 50°: (Y =) H, 1.0; p-OMe, 0.12; p-Cl, ca. 32; m-Cl, ca. 84. (iii) For PhNHSiR₃ compounds in MeOH (5 vol) + aq. alkali (2 vol) : (R₃ =) Et₃, 1.0; Et₂Me, 18 (at 30°); Me₂-i-Pr, 8 (at 30°);Me₂-t-Bu, 0.012 (at 50°);i-Pr₃, 0.006 (at 50°). In series (i) the relative rates correlate with σ, or where appropriate σ^?-constants, with a ? value of 1.6. It is suggested that in the transition state of the rate-determining step the OSi bond is fully formed, or almost so, the SiN bond approximately 20—50% broken, and the bond between the nitrogen atom and a proton from the solvent ca. 10—30% formed.     

Kottamide E, the first example of a natural product bearing the amino acid 4-amino-1,2-dithiolane-4-carboxylic acid (Adt)

Kottamide E, a novel alkaloid containing dibrominated indole enamide, oxalic acid diamide and 4-amino-1,2-dithiolane-4-carboxamide moieties, has been isolated from the New Zealand ascidian Pycnoclavella kottae. Characterisation was achieved by interpretation of spectroscopic data.     

The effects of molecular reorientation on the absorption of intense light by organic-dye solutions

Equations are presented for the spectral and orientational distribution of unexcited dye molecules in the field of an intense giant laser pulse. The solute dye molecules are linear oscillators that may be broadened either homogeneously or inhomogeneously, and may reorient by sudden jumps over large angles or by small angular steps (brownian rotational motion). The equations are employed to analyze the intensity dependence of fluorescence polarization observed by Mourou and Denariez-Roberge for the system cryptocyanine-glycerin. Their data are consistent with an excited-state deactivation time T₁ = 0.4 ± 1.0 ns and a rotational diffusion constant D = 20/T₁ = 5.0 × 10⁹ s⁻¹     

Are dipolar liquids ferroelectric?

VH and HV depolarized hyper-Rayleigh scattering spectra were measured for liquid solutions of dipolar CH3CN in nondipolar C2Cl4 at T=300 K. The VH spectrum contains a strong narrow peak due to a slowly relaxing longitudinal orientation mode. This peak is absent in the HV spectrum, and it disappears from the VH spectrum when the CH3CN concentration is reduced to 8%. This observation is consistent with a ferroelectric phase transition predicted to occur when rho mu0(2)=9epsilon0kT=49 D2 M.     

High accuracy ab initio studies of Li6+, Li6-, and three isomers of Li6

The structures and energetics of Li(6) (+), Li(6) (-) and three isomers of Li(6) are investigated using the coupled-cluster singles, doubles and perturbative triples [CCSD(T)] method with valence and core-valence correlation consistent basis sets of double- to quadruple-zeta quality (cc-pVXZ and cc-pCVXZ, where X=D-Q). These results are compared with qualitatively different predictions by less reliable methods. Our results conclusively show that the D(4h) isomer is the global minimum structure for Li(6). It is energetically favored over the C(5v) and D(3h) structures by about 5.1 and 7.1 kcal mol(-1), respectively, after the inclusion of the zero-point vibrational energy (ZPVE) correction. Our most accurate total atomization energies are 123.2, 117.6, and 115.7 kcal mol(-1) for the D(4h), C(5v), and D(3h) isomers, respectively. Comparison of experimental optical absorption spectra with our computed electronic spectra also indicate that the D(4h) isomer is indeed the most stable structure. The cation, anion, and some higher spin states are investigated using the less expensive cc-pCVDZ basis set. Adiabatic ionization energies and electron affinities are reported and compared with experimental values. Predictions of molecular properties are found to be sensitive to the basis set used and to the treatment of electron correlation.