Stilbene-hexane

A. H. Zewail To provide a partial answer to the question of Prof. Hamaguchi, the structure of the 1 1 stilbene-hexane species was determined with the help of rotational coherence spectroscopy. For higher clusters we used atom-atom model potentials and deduced structures. 

Figure A3.6.8. Isothemis of k ) for tran.s-stilbene photoisomerization in n-hexane at temperatures between...

Fig. 13.10. UV spectra of -and Z-stilbene in hexane at room temperature. [From H. Meier Angew. Chem. Int. Ed. Engl. 31 1399 (1992), Reproduced by permission of Wiley-VCH.

A 500-ml. three-necked flask is fitted with a reflux condenser and a thermometer, the bulb of which reaches far enough into the flask to be covered by the liquid. A solution of 46.0 g. (0.205 mole) of a-phenylcinnamic acid (p. 70) (Note 1) in 280 ml. (307 g., 2.38 moles) of quinoline (Note 2) is added to the flask along with 4.0 g. of copper chromite.2 The reaction flask is heated by means of a mantle or an oil bath until the temperature of the reaction mixture reaches 210-220°. The mixture is kept within this temperature range for 1.25 hours. The solution is then cooled immediately and added to 960 ml. of 10% hydrochloric acid in order to dissolve the quinoline (Note 3). The product is extracted from this mixture with two 200-ml. portions of ether followed by a 100-ml. portion. The combined ether extracts are filtered to remove particles of catalyst, washed with 200 ml. of 10% sodium carbonate, and dried over anhydrous sodium sulfate. The dry solution is removed from the drying agent by filtration and heated on a steam bath to distil the ether. The residue is dissolved in a hexane fraction, b.p. 60-72° (Skellysolve B) the solution is cooled to 0° and filtered to remove /raws-stilbene, if any. The hydrocarbon solvent is removed by distillation, and the czs-stilbene is distilled. The yield is 23-24 g. (62-65%), b.p. 133-136°/10 nun., 95-97°/l mm. tig 1.6183-1.6193, 1.6212-... 

The same authors also reported the dispersion of palladium nanoparticles in a water/AOT/n-hexane microemulsion by hydrogen gas reduction of PdClJ and its efficiency for hydrogenation of alkenes in organic solvents [79]. UV-visible spectroscopy and TEM analysis revealed the formation of Pd nanoparticles with diameters in the range of 4 to 10 nm. Three olefins (1-phenyl-l-cyclohexene, methyl trans-cinnamate, and trans-stilbene) were used as substrates for the catalytic hydrogenation experiments under 1 atm of H2 (Table 9.12). All of the Start-... 

The crude material was purified by flash chromatography on silica gel (60 g), buffered with 1 % of triethylamine, using w-hexane-diethyl ether (95 5) to afford (R,R)-( )-stilbene oxide as a colourless oil (123 mg, 0.62 mmol, 62%). 

The hydroxylation of n-hexane and epoxidation of stilbens were conducted at 300K in the suspended solutions with PhIO for each powdered sample such as FePc(t-Bu)4/NaY, FePc(t-Bu)4+NaY, FePc/NaY and FePc+NaY. The products in solution were filtered and analyzed by FID gc using a capillary column(PEG-25M). 

Microscopic Friction and Solvation in Barrier Crossing Isomerization of Stilbene in Size-Selected Hexane Clusters, A. A. Heikal, S. H. Chong, J. S. Baskin, and A. H. Zewail, Chem. Phys. Lett. 242, 380 (1995). 

H. Hamaguchi What information do you have concerning the structure and dynamics of the hexane-dressed stilbene molecule How flexible or how rigid is the structure ... 

FIGURE 10. Relative quantum yields for exciplex fluorescence (filled symbols) and addition product formation (open symbols) versus solvent dielectric constant for trans-stilbene with di isopropyl methyl amine (0)> ethyldiisopropylamine (A), and triethylamine ( ) in hexane-ethyl acetate and ethyl acetate-acetonitrile mixed solvents. From ref. (114) with permission of the American Chemical Society. 

E-Stilbene (18 mg, 0.1 mmol) and ketone (3.8 mg, 0.01 mmol) were dissolved in CH3CN (1.5 mL) at r.t. An aqueous Na2(EDTA) solution (1 mL, 4 x 10-4 M) was added. To the stirred mixture was added in portions a mixture of Oxone (307 mg, 0.5 mmol) and sodium bicarbonate (130 mg, 1.55 mmol). On completion of the reaction according to TLC analysis (20 min), the reaction mixture was poured into water (20 mL) and extracted with CH2CI2 (3 x 20 mL). The combined organic layers were dried over anhydrous Na2S04. After removal of the solvent under reduced pressure, the residue was purified by flash column chromatography on silica gel (hexane, then 95 5 hexanes ethyl acetate) to give trans-stilbene epoxide (19.4 mg, 99% yield) in 47% ee. 

E-Stilbene (0.181 g, 1 mmol) was dissolved in 1 2 acetonitrile DMM (15 mL). To this solution were added buffer (10 mL, 0.05 M solution of Na2B4O7l0H2O in 4 x 10-4 M aqueous Na2(EDTA)), tetrabutylammonium hydrogen sulfate (0.015 g, 0.04 mmol), and ketone catalyst (77.4 mg, 0.3 mmol). The mixture was cooled in an ice bath. A solution of Oxone (0.85 g, 1.38 mmol) in aqueous Na2(EDTA) (4 x 10-4 M, 6.5 mL) and a solution of K2CO3 (0.8 g, 5.8 mmol) in water (6.5 mL) were added dropwise separately over a period of 1.5 h (via syringe pumps or addition funnels). The best results were obtained if these solutions were added in a steady, uniform manner. After 2 h, the reaction was diluted with water (30 mL), and extracted with hexanes (4 x 40 mL). The combined extracts were washed with brine, dried (Na2S04), filtered, concentrated, and purified by FC on silica gel (previously buffered with 1% triethylamine solution in hexane) using 1 0 to 50 1 hexane ether as eluent. This provided trans-stilbene oxide (0.153 g, 78%) with 98.9% ee. 

The progress of the epoxidation can be followed by measuring periodically the optical density of the reaction mixture at 295 m/x. The reaction time and temperature specified in the procedure were found to reduce the optical density of the reaction mixture at 295 m/x (and, accordingly, the /rans-stilbene concentration) to less than 3% of its initial value. If more than this amount of unchanged fraws-stilbene remains in the crude product, it cannot be removed by recrystallization from either methanol or hexane. Even after repeated crystallization the melting point of the product does not rise above 66-67°. Pure fraws-stilbene oxide can be isolated from such a mixture if the mixture is treated with additional peracetic acid to convert the remaining fraras-stilbene to fraws-stilbene oxide. 

The time-resolved Raman spectra of the S, state of trans-stilbene were measured in a 3x10 mol dm hexane solution (Figure 1(a)). The 1160 to 1200 cm region is expanded in Figure 1(b). From the rigure, it is clear that e position and the width of the 1180 cm band change as the time delay increases. 

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