The conformational equilibrium of 1,3-dichloro-5-methylcyclohexane

Two of the stereoisomers of the title compound were prepared and their dipole moments were measured. For the r-1,c-3-dichloro-t-5-methylcyclohexane, the free energy difference between conformers with axial-axial (aa) and equatorial-equatorial (ee) chlorines was measured by a variable temperature NMR method, and the value found was 1.3 ± 0.2 Kcal/mol^-1 (in acetone) favoring the latter. Molecular mechanics studies show that the solvation energy and the electrostatics are of major importance in understanding this equilibrium. Calculations show the effect of the methyl group is essentially additive, and give for cis-1,3-dichlorocyclohexane itself ee?aa DH+ 3.0 kcal mol^-1 (acetone).     

Imine Reduction with Me2S-BH3

Although there exists a variety of different catalysts for hydroboration of organic substrates such as aldehydes, ketones, imines, nitriles etc., recent evidence suggests that tetra-coordinate borohydride species, formed by activation, redistribution, or decomposition of boron reagents, are the true hydride donors. We then proposed that Me₂S-BH₃ could also act as a hydride donor for the reduction of various imines, as similar compounds have been observed to reduce carbonyl substrates. This boron reagent was shown to be an effective and chemoselective hydroboration reagent for a wide variety of imines.     

Influence of (0, 1)* Laguerre-Gaussian Field Distribution on Tunneling Ionization Rate

Journal of Experimental and Theoretical Physics - In the frame of the ADK theory, the tunneling ionization of an argon atom exposed to the light from Ti:Sapphire laser is investigated. We assume...     

A Well‐Defined Aluminum‐Based Lewis Acid as an Effective Catalyst for Diels–Alder Transformations

A catalytically active aluminum‐based system for Diels–Alder transformations is reported. The system was generated by mixing a β‐diketiminate‐stabilized aluminum bistriflate compound with Na[BAr^Cl₄] (Ar^Cl=3,5‐Cl₂C₆H₃). Solid‐state analysis of the catalytic system reveals a unique structure incorporating a two‐dimensional coordination polymer. According to the experimental results obtained from several Diels–Alder transformations, the aluminum‐based system appears to be a more practical and more robust alternative to the recently reported compounds based on carbon and silicon cations.     

Oxidation of a P−C Bond under Mild Conditions

The reactivity of phosphenium dication [(Ph₃P)₂C‐P‐NiPr₂]²⁺, 1²⁺ , towards pyridine N‐oxide (O‐py) has been investigated. The resulting oxophosphonium dication [(Ph₃P)₂C(NiPr₂)P(O)(O‐py)]²⁺, 2²⁺ , was surprisingly stabilized by a less nucleophilic O‐py ligand instead of pyridine (py). This compound was then identified as an analogue of the elusive Criegee intermediate as it underwent oxygen insertion into the P?C bond through a mechanism usually observed for Baeyer–Villiger oxidations. This oxygen insertion appears to be the first example of a Baeyer–Villiger oxidation involving O‐py.     

Cationic terminal gallylene complexes by halide abstraction: coordination chemistry of a valence isoelectronic analogue of CO and N2

While N(2) and CO have played central roles in developing models of electronic structure, and their interactions with transition metals have been widely investigated, the valence isoelectronic diatomic molecules EX (E = group 13 element, X = group 17 element) have yet to be isolated under ambient conditions, either as the "free" molecule or as a ligand in a simple metal complex. As part of a program designed to address this deficiency, together with wider issues of the chemistry of cationic systems [L(n)M(ER)](+) (E = B, Al, Ga; R = aryl, amido, halide), we have targeted complexes of the type [L(n)M(GaX)](+). Halide abstraction is shown to be a viable method for the generation of mononuclear cationic complexes containing gallium donor ligands. The ability to isolate tractable two-coordinate products, however, is strongly dependent on the steric and electronic properties of the metal/ligand fragment. In the case of complexes containing ancillary pi-acceptor ligands such as CO, cationic complexes can only be isolated as base-trapped adducts, even with bulky aryl substituents at gallium. Base-free gallylene species such as [Cp*Fe(CO)(2)(GaMes)](+) can be identified only in the vapor phase by electrospray mass spectrometry experiments. With bis(phosphine) donor sets at the metal, the more favorable steric/electronic environment allows for the isolation of two-coordinate ligand systems, even with halide substituents at gallium. Thus, [Cp*Fe(dppe)(GaI)](+)[BAr(f)(4)](-) (9) can be synthesized and shown crystallographically to feature a terminally bound GaI ligand; 9 represents the first experimental realization of a complex containing a valence isoelectronic group 13/group 17 analogue of CO and N(2). DFT calculations reveal a relatively weakly bound GaI ligand, which is confirmed experimentally by the reaction of 9 with CO to give [Cp*Fe(dppe)(CO)](+)[BAr(f)(4)](-). In the absence of such reagents, 9 is stable for weeks in fluorobenzene solution, presumably reflecting (i) effective steric shielding of the gallium center by the ancillary phosphine and Cp* ligands; (ii) a net cationic charge which retards the tendency toward dimerization found for putative charge neutral systems; and (iii) (albeit relatively minor) population of the LUMOs of the GaI molecule through pi overlap with the HOMO and HOMO-2 of the [Cp*Fe(dppe)](+) fragment.     

Influence of cubic α-Fe2O3 particles on the thermal stability of poly(methyl methacrylate) synthesized by in situ bulk polymerization

Poly(methyl methacrylate)/α-Fe₂O₃ composites were prepared by in situ bulk radical polymerization of methyl methacrylate in the presence of the cubic α-Fe₂O₃ particles using 2,2′-azobisisobutyronitrile as initiator. The cubic α-Fe₂O₃ particles were synthesized by forced hydrolysis of FeCl₃ and characterized by X-ray diffraction analysis and transmission electron microscopy. The molar masses and molar mass distribution of synthesized PMMA samples were determined by gel permeation chromatography. The influence of α-Fe₂O₃ filler particles on the thermal properties of the PMMA matrix was investigated using thermogravimetry and differential scanning calorimetry. The molar mass and polydispersity of PMMA extracted from composite samples were not influenced by cubic α-Fe₂O₃ particles. The obtained composites have better thermal and thermooxidative stability than pure PMMA. On the other hand, the values of the glass transition temperature of composite samples were identical to the glass transition temperature of pure PMMA.     

Unusually kicked dynamics: Hydrogen atom in a spherical box

In this paper we have examined the ionization of the ground state hydrogen atom in a spherical box with laser pulses of specific shapes. These shapes are predicted assuming correspondence under some conditions with the alternating kicking field. Unusually kicked dynamics is suggested. It is shown that such kicked dynamics leads to generalized Rabi oscillations with the positive energy states included and participation of the excited states. The correspondence with the real pulse is established emphasizing such unusually kicked dynamics. The approach is verified on the one-dimensional (1D) hydrogen atom and calculation of the known results for ionization probability.