Conjugate addition of (trimethylstannyl)copper reagents to α,β-acetylenic N,N-dimethylamides. Trapping of the intermediates with electrophiles

A study of the reaction of Me₃SnCu·.Me₂S (1) and [Me₃SnCuSPh]Li (2) with α,β - acetylenic N,N-dimethylamides 3 shows (a) that the overall process can be controlled experimentally so as to produce either N,N-dimethyl ($\text{E}$)-(4) or ($\text{Z}$)-3-trimethylstannyl-2-alkenamides (5), (b) that the initially formed intermediate derived from interaction of 2 and 3 is significantly more stable than that obtained by reaction of 2 and α,β-acetylenic esters, and (c) that the intermediate produced by treating 3 with 1 can be trapped with electrophiles other than proton.     

The mass spectra of some silver salts

Fifteen of twenty-four silver(I) carboxylates examined give useful electron impact mass spectra. The compounds vaporize at moderate temperatures, apparently mainly as dimer with traces of higher oligomer in only a few cases. The molecular ion for the dimer is generally weak or absent, with the most abundant silver containing ion being [Ag₂(O₂CR)]⁺ in most cases. Metastable defocusing and deuterium labeling experiments on silver acetate have established some of the fragmentation pathways. The reported loss of carbon dioxide from perfluorocarboxylates to give intense peaks for organosilver ions was not observed in this study. Attempts to obtain spectra on the silver salts of organic materials other than carboxylic acids were successful in several cases. Silver trifluoromethanesulfonate, although much less volatile, gives a spectrum and fragmentation very much like the carboxylates, whereas silver trifluoromethanethiolate gives a complex spectrum which suggests tetramer as a major gas phase species. Of three compounds examined which have silver to nitrogen bonding only silver(II) phthalocyanine is sufficiently volatile to give a spectrum without decomposition. The field desorption spectra of the four compounds examined all show the ions Ag_nX_{n ? 1} for X=acetate (n=1 ? 6), X=p-chlorobenzoate (n=1 ? 4), X=methanesulfonate (n=1 ? 7) and X=p-toluenesulfonate (n=1 ? 5).     

Yield of 16OS18O from the 18OH initiated oxidation of CS2 in 16O2

The yield of ¹⁶OS¹⁸O from the ¹⁸OH initiated oxidation of CS₂ in ¹⁶O₂ was measured by using a discharge flow reactor coupled to a chemical ionization mass spectrometer. ¹⁶OS¹⁸O is the dominant SO₂ isotopomer produced with a yield of 0.90 ± 0.20 relative to ¹⁸OH loss. The errors are estimates for the uncertainty at the 95% confidence level. The implications of these results to the understanding of the CS₂ oxidation mechanism are discussed. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Elution order in gas chromatography

The retention behavior of a heterogeneous group of solutes has been examined on seven different stationary phases under isothermal and temperature-programmed conditions. Both ΔH_v (enthalpy of solute vaporization from the stationary phase) and ΔS_v (entropy of solute vaporization from the stationary phase) values were determined for each solute – stationary phase combination under isothermal conditions. Both program rate and carrier gas velocity were shown to affect solute elution order. Unless these and other experimental factors discussed are controlled, column equivalency studies based on solute elution order have dubious value.     

Barrierless electron transfer bond fragmentation reactions

The ultrafast N-O bond fragmentation in a series of N-methoxypyridyl radicals, formed by one-electron reduction of the corresponding N-methoxypyridiniums, has been investigated as potentially barrierless electron-transfer-initiated chemical reactions. A model for the reaction involving the electronic and geometric factors that control the shape of the potential energy surface for the reaction is described. On the basis of this model, molecular structural features appropriate for ultrafast reactivity are proposed. Femtosecond kinetic measurements on these reactions are consistent with a kinetic definition of an essentially barrierless reaction, i.e., that the lifetime of the radical is a few vibrational periods of the fragmenting bond, for the p-methoxy-N-methoxypyridyl radical.     

Application of the energy gap law to the decay of charge transfer excited states,solvent effects

Values of non-radiative decay rate constants (k_nr) and emission energies (E_cm) have been obtained for Os(Phen₃)²⁺ in a series of solvents and the results are consistent with the energy gap law. For hydroxylic solvents like water or methanol related studies suggest the existence of strong, specific contributions to the vibrational trapping energy of the solvent.     

Equivalence of vacuum Yang-Mills gravitation and vacuum Einstein gravitation

In the Yang-Mills formulation of gravitational dynamics based uponSL(2,C) spin transformations acting on Dirac spinors, the vacuum field equations are R +C R = 0 and and . HereR is the Ricci curvature andC is the Weyl conformal curvature; is a coupling constant. We show the equivalence between solutions of these equations and the vacuum Einstein equationsR = 0. The proof uses the Newman-Penrose formalism.Supported by a NATO fellowship.Supported by a SRC fellowship.     

Photophysics of aromatic molecules with low-lying pi sigma* states: excitation-energy dependence of fluorescence in jet-cooled aromatic nitriles

Excitation-energy dependence of fluorescence intensity and fluorescence lifetime has been measured for 4-dimethylaminobenzonitrile (DMABN), 4-aminobenzonitrile (ABN), 4-diisopropylaminobenzonitrile (DIABN), and 1-naphthonitrile (NN) in a supersonic free jet. In all cases, the fluorescence yield decreases rather dramatically, whereas the fluorescence lifetime decreases only moderately for S1 (pi pi*, L(b)) excess vibrational energy exceeding about 1000 cm(-1). This is confirmed by comparison of the normalized fluorescence excitation spectrum with the absorption spectrum of the compound in the vapor phase. The result indicates that the strong decrease in the relative fluorescence yield at higher energies is due mostly to a decrease in the radiative decay rate of the emitting state. Comparison of the experimental results with the TDDFT potential energy curves for excited states strongly suggests that the decrease in the radiative decay rate of the aminobenzonitriles at higher energies is due to the crossing of the pi pi* singlet state by the lower-lying pi sigma*(C[triple bond]N) singlet state of very small radiative decay rate. The threshold energy for the fluorescence "break-off" is in good agreement with the computed energy barrier for the pi pi*/pi sigma* crossing. For NN, on the other hand, the observed decrease is in fluorescence yield at higher excitation energies can best be attributed to the crossing of the pi pi* singlet state by the pi sigma* triplet state.     

Deuterium isotope effects on hydrophobic interactions: the importance of dispersion interactions in the hydrophobic phase

Hydrogen/deuterium isotope effects on hydrophobic binding were examined by means of reversed-phase chromatographic separation of protiated and deuterated isotopologue pairs for a set of 10 nonpolar and low-polarity compounds with 10 stationary phases having alkyl and aryl groups bonded to the silica surface. It was found that protiated compounds bind to nonpolar moieties attached to silica more strongly than deuterated ones, demonstrating that the CH/CD bonds of the solutes are weakened or have less restricted motions when bound in the stationary phase compared with the aqueous solvent (mobile phase). The interactions responsible for binding have been further characterized by studies of the effects of changes in mobile phase composition, temperature dependence of binding, and QSRR (quantitative structure-chromatographic retention relationship) analysis, demonstrating the importance of enthalpic effects in binding and differentiation between the isotopologues. To explain our results showing the active role of the hydrophobic (stationary) phase we propose a plausible model that includes specific contributions from aromatic edge-to-face attractive interactions and attractive interactions of aliphatic groups with the pi clouds of aromatic groups present as the solute or in the stationary phase.     

Phosphorus-based SAHA analogues as histone deacetylase inhibitors

[structure: see text] Three analogues of suberoyl anilide hydroxamic acid (SAHA) with phosphorus metal-chelating functionalities were synthesized as inhibitors of histone deacetylases (HDACs). The compounds showed weak activity for HeLa nuclear extracts (IC(50) = 0.57-6.1 mM), HDAC8 (IC(50) = 0.28-0.41 mM), and histone-deacetylase-like protein (HDLP, IC(50) = 0.33-1.9 mM), suggesting that the transition state of HDAC is not analogous to zinc proteases. Antiproliferative activity against A2780 cancer cells (IC(50) = 0.11-0.12 mM), comparable to SAHA (0.15 mM), was observed.