Inelastic electron tunneling spectroscopy of an alkanethiol self-assembled monolayer using scanning tunneling microscopy

We report inelastic electron tunneling spectroscopy (IETS) of a C8 alkanethiol self-assembled monolayer using a scanning tunneling microscope (STM). High-resolution STM IETS spectra show clear features of the C-H bending and C-C stretching modes in addition to the C-H stretching mode, which enables a precise comparison with previously reported vibrational spectroscopy, especially electron energy loss spectroscopy data. Intensity variation of vibrational peaks with tip position is discussed with the STM IETS detection mechanism.     

Sulfide extrusion from the methylsulfonium salts of 8-thiabicyclo [3.2.1]oct-2-enes and the related sulfonium salts by methyllithium

The methysulfonium salts of 2-methylene-8-thiabicyclo[3.2.1]octane and 8-thiabicyclo[3.2.1]oct-2-enes underwent sulfide extrusion by methyllithium to give dimethyl sulfide and the hydrogen shift products (cycloheptadienes) and/or the closure products (bicycloheptenes).     

Effects of substituents on chain-transfer reactivities of p-substituted cumenes in radical polymerization of p-substituted styrenes

In order to study the effects of the substituents in both substrate and attacking radical on the chain-transfer reactivities of nuclear-substituted cumenes toward substituted polystyryl radicals, the polymerizations of p-substituted styrenes in the presence of p-substituted cumenes were carried out with α,α′-azobisisobutyronitrile as an initiator at 60°C, and their chain-transfer constants were determined. The relative chain transfer reactivities of p-substituted cumenes toward given p-substituted polystyryl radicals did not follow the Hammett equation, but were correlated with the modified Hammett equation, log(k/k₀) = pρ + γE_R, which was proposed by the present authors for evaluating the substituent effects in radical reactions. On the other hand, the relative reactivities of poly-(p-substituted styrene) radicals toward given p-substituted cumenes were correlated by the Hammett equation. Thus, it was concluded that the effects of the substituents in substrate cumene depended upon the contributions of both polar and resonance factors, while those in attacking polystyryl radical depended upon only a polar factor.     

Salt effects in the binding of 4-(1-pyrenyl)-butyltrimethylammonium to poly(vinylbenzo-18-crown-6) and poly(vinylbenzoglyme) in water

The binding of 4¹-(1-pyrenyl)butyltrimethylammonium bromide (PN⁺) to the neutral poly-soap-type polymers poly(vinylbenzo-18-crown-6) (P18C6) and poly(vinylbenzoglyme) (PVBG) was studied by optical spectroscopy and fluorescence in the presence and absence of salts. Measurements of the respective binding constants were based on distinct differences in the optical absorption spectra of free and polymer-bound PN⁺. When crown ether-compelxable cations (e.g., K⁺) were added the adsorption of PN⁺ to P18C6 decreased as the neutral polymer was converted to a polycation. No decrease was found with PVBG because alkali ions do not complex significantly to this polymer in water. PN⁺ adsorption to both polymers rose rapidly, however, as the salt concentration increased. This effect was strongly anion-dependent and increased in the order of Cl^? < Br^? < I^? < CNS^? < BPh₄?. The increased binding was reflected in a higher binding constant and also in a larger number of bound PN⁺ molecules per polymer chain under saturation conditions. It is argued that the formation of ion pairs or larger ion clusters in the aqueous phase when anions are added forces more PN⁺ molecules to adsorb on the surface of the polymer coil to which they are bound as ion pairs or higher aggregates. Under saturation conditions enough PN⁺ molecules are bound to convert the pyrene monomer fluorescence spectrum into that of the excimer. These results are compared with data obtained for the anionic solute 4-(1-pyrenyl)butanoate in the presence of salts.     

Facile deoxygenation of dicarbonyl compounds using a samarium diiodide-additive system

The reduction of alpha- and beta-dicarbonyl compounds was investigated with samarium diiodide in the presence of additive. Diketones and ketocarboxylic acids were easily reduced at room temperature to give the mono-alcohols in good to excellent yield, and ketoester afforded the saturated ester as the major product in moderate yield. These reductions containing the reductive deoxygenation can be rapidly performed under the facile and mild conditions by this method.     

Tetrasilacyclobutadiene ((t)Bu(2)MeSi)(4)Si(4): a new ligand for transition-metal complexes

The anionic complex of [tetrakis(di-tert-butylmethylsilyl) tetrasilacyclobutadiene]dicarbonylcobalt, [(R4Si4)Co(CO)2]-.K+ (R = SiMetBu2) 2-.K+, was synthesized by the reaction of tetrasilacyclobutadiene dianion dipotassium salt [R4Si4]2-.2K+ 1 with an excess of CpCo(CO)2 in THF. X-ray analysis of 2-.[K+(diglyme)2(THF)] showed an almost planar Si4 ring of rectangular shape with an in-plane arrangement of the silyl substituents. 2- was also prepared as a free anion with the [K+[2.2.2]cryptand] counterion by complexation with [2.2.2]cryptand and as a dimer {2-.[K+(THF)3]}2 without complexing reagents in THF. Such a tetrasilacyclobutadiene fragment represents a new type of ligand for Co complexes, being the first example of a cyclobutadiene containing only heavier group 14 elements.     

Curve-structured phenalenyl chemistry: synthesis, electronic structure, and bowl-inversion barrier of a phenalenyl-fused corannulene anion

We have demonstrated the features of curve-structured phenalenyl chemistry, for the first time. A phenalenyl-fused corannulene anion has been designed by the annelation of a six-memberd ring across peri-positions of corannulene and generated as a stable species in a degassed solution. The 1H and 13C NMR spectra have shown the highly symmetrical structure and high-field shifts of protons and carbons at the asterisked positions in the chemical structure, indicating the occurrence of large negative charge densities at these positions. These results well agree with the HOMO picture and the electrostatic potential surface, demonstrating the phenalenyl anion-type electronic structure is retained in the curved-surface pi-system. The calculated bowl-inversion barrier of the anion (11.3 kcal/mol) is larger than that of corannulene (9.2 kcal/mol) because of peri-annelation of the corannulene skeleton. The calculations of the barriers of the neutral radical (12.6 kcal/mol), radical dianion (8.1 kcal/mol), and trianion (5.4 kcal/mol) of the phenalenyl-fused corannulene have exhibited a stepwise flattening of the curvature with increase in negative charge. Therefore, we have revealed that the bowl-inversion barrier of the anion is governed by the setoff of the peri-annelation and negative charge effects.     

Adiabatic calorimetry of the metallomesogen purple cobalt stearate Co(O2CC17H35)2

The heat capacity of the metallomesogen purple cobalt stearate Co(O₂CC₁₇H₃₅)₂ has been measured by adiabatic calorimetry at temperatures between 16 and 420?K. This compound exhibits two crystalline phases (low temperature Cr2 and high temperature Cr1 phases), mesophase (M phase), and isotropic liquid (I phase). A third crystalline phase Cr3, which is entirely metastable with respect to all the others, is suggested by DSC studies. The Cr2-to-Cr1, Cr1-to-M, and M-to-I phase transitions occurred at 362.1, 380.9, and 400.4?K, respectively. The enthalpy and entropy gains at these phase transitions were determined. The mesophase is either smectic A or nematic.