Stereodynamics of 9,11-Diphenyl-10-azatetracyclo[6.3.0.0.(4,11)0.(5,9)]undecanes. Highly Restricted Nitrogen Inversion and Isolated Phenyl Rotation. X-ray Crystallographic, Dynamic NMR, and Molecular Mechanics Studies

The (1)H NMR spectra of 10-benzyl-9,11-diphenyl-10-azatetracyclo[6.3.0.0.(4,11)0.(5,9)]undecane (BnPh(2)()) and 10-methyl-9,11-diphenyl-10-azatetracyclo[6.3.0.0.(4,11)0.(5,9)]undecane (MePh(2)()) decoalesce due to slowing inversion at nitrogen and to slowing isolated bridgehead phenyl rotation. The high nitrogen inversion barriers in MePh(2)() (DeltaG() = 12.2 +/- 0.1 kcal/mol at 250 K) and BnPh(2)() (DeltaG() = 10.6 +/- 0.1 kcal/mol at 215 K) are typical of tertiary amines in which at least one C-N-C bond angle is constrained to a small value. Compared to the minuscule rotation barriers about sp(2)-sp(3) carbon-carbon bonds in simple molecular systems, the bridgehead phenyl rotation barriers in MePh(2)() (DeltaG() = 9.8 +/- 0.1 kcal/mol at 210 K) and BnPh(2)() (DeltaG() = 9.8 +/- 0.1 kcal/mol at 210 K) are unusually high. Molecular mechanics calculations (MMX force field) suggest that the origin of the high phenyl rotation barriers lies in the close passage of an o-phenyl proton and a methyl (or benzylmethylene) proton in the transition state. BnPh(2)() crystallized from hexane as white needles in the monoclinic system Pn. Unit cell dimensions are as follows: a = 12.198(1) ?, b = 6.1399(6) ?, c = 14.938(2) ?, beta = 107.470(4) degrees, V = 1067.1(2) ?(3), Z = 2. In the crystal molecular structure, the imine bridge CNC bond angle in BnPh(2)() is constrained to a small value (96 degrees ). The benzylic phenyl group is oriented gauche to the nitrogen lone pair.     

The level structure of92Ru up to high spin values

The level structure of⁹²Ru has been studied by means of γ-ray spectroscopy. The nucleus was produced by the⁵⁸Ni(⁴⁰Ca, α2p)⁹²Ru reaction at beam energies of 147 and 187 MeV. The NORDBALL detector system including particle selection was used. A large number of new levels with excitation energies up to 11.3 MeV and spin values up to 22 or 23 units of angular momentum have been established. The level scheme is compared with recent shell model calculations using¹⁰⁰Sn as a core. Some systematics of the g ₉ ^2/?2 configuration is discussed and a strong correlation between the levels in⁹⁰Mo and⁹²Ru is found.     

Syntheses of Theaspirone and Vitispirane via Palladium(II)-Catalyzed Oxaspirocyclization

Total syntheses of theaspirone (A and B) and vitispirane (A and B) are described. The key step in the syntheses is the palladium(II)-catalyzed intramolecular oxaspirocyclization of diene alcohol 4 to either vitispirane or the allylic alcohol 9. The outcome of the oxaspirocyclization is very much dependent on the solvent employed. In water-acetic acid (4:1) a 1:1 mixture of the diastereomeric alcohols 9A and 9B was exclusively formed. In water with 8 equiv of a strong non-nucleophilic acid, vitispiranes A and B (1:1) were obtained. An alternative procedure to obtain vitispirane with the use of LiCl and K(2)CO(3) is described. In the latter reaction vitispirane B is formed preferentially. This result is explained by an equilibrium between the two possible pi-allyl complexes 5A and 5B, the kinetically favored 5B being transformed into vitispirane 3B before isomerization to 5A occurs.     

Flow-through microdispenser for interfacing micro-HPLC to Raman and mid-IR spectroscopic detection

A flow-through microdispenser has been coupled to a micro HPLC separation system and used as a solvent elimination interface for Fourier transform infrared (FTIR) and Raman spectroscopic detection of the separated compounds. Using the microdispenser picoliter sized droplets can be generated and deposited on an appropriate target placed on a computerized x, y-stage. Evaporation of volatile solvent and buffer is rapid and allows analysis of the obtained dry deposits by various techniques. Due to the destruction free character of Raman and FTIR spectroscopy they can be applied sequentially to interrogate the same deposit. In the reported application five phenolic acids typically present in wine have been separated on a C-18 column technique using a mixture of water, methanol and acetic acid as mobile phase. For spectrum acquisition infrared and Raman microscopes have been used. The spectra recorded from the dried deposits of the separated compounds agreed well with the reference spectra of corresponding components.     

Comparison of denuder and impinger sampling for determination of gaseous toluene diisocyanate (TDI)

An air-sampling method employing denuders coated inside with a chemisorptive stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precision of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limit of determination (LOD) of the method, including LC-APCI-MS-MS analysis, was found to be 1.9 microg m(-3) and 1.2 microg m(-3) for 2,4- and 2,6-TDI, respectively, for short-term measurements (15 min). Significant lower LOD was obtained for long-term measurements. This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time-weighted average) exposure limit, which is 40 microg m(-3) for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampling with no loss in performance. The contents of denuders should, on the other hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed.     

Zur regioselektiven nucleophilen Addition an 2,3-Dihydrobilatriene-abc

Donors are added regioselectively to position 10 of 2,3-dihydrobilatrienes-abc in a reversible reaction, which is complicated in case of strongly basic donors due to the easy deprotonation of the partially saturated ring. Compared to the bilatrienes-abc the addition equilibrium is retarded by about two orders of magnitude.