J.M. Pechine

MEASUREMENT OF THE OPTICAL PURITY OF FLUORINATED COMPOUNDS USING PROTON DECOUPLED 19F NMR SPECTROSCOPY IN A CHIRAL LIQUID CRYSTAL SOLVENT

The use of trifluoroacetic anhydride as an achiral derivatizing agent for enantiomeric excess measurement through chiral liquid crystal NMR is described. Examples involving amines, amino acids and alcohols are provided. It is shown that the proton decoupled fluorine NMR spectra of the -CO-CF3 group allow good enantiomeric discrimination based on both the chemical shifts and the dipolar splitting. The spectra separation is due to the differential ordering effect of enantiomers in the oriented chiral solvent. The results are then compared to the discriminating power of the -CO-CD3 group that has been previously described using deuterium NMR in the same anisotropic medium.

Flash vacuum thermolysis of β-keto-trimethylsilyl-enol-ethers: Synthesis of allenic and furanic derivatives

Abstract Thermolysis at 800° of a series of β-keto-trimethylsilyl-enol-ethers allows the elimination of a trimethylsilanol molecule through a 1,5 rearrangement. The reaction products are furanic derivatives, which are obtained in often good yields through an allenic intermediate, which has been isolated.

Preparation and characterization of “furanoradialene” (tetramethylene - tetrahydrofuran)

Abstract Tetramethylene-tetrahydrofuran has been prepared by flash vacuum thermolysis. This compound is stable in solution below −50° C, and was characterized by NMR and mass spectrometry.

Preparation and characterization of 2,3-dihydro-2,3 bis (methylene) furan

Abstract 2,3-dihydro-2,3 bis (methylene) furan and its 4-methyl derivative have been prepared by flash vacuum thermolysis and characterized by mass spectrometry and chemical trapping.

An achiral deuterated derivatizing agent for enantiomeric analysis through NMR in a liquid crystalline solvent

Abstract The application of a ‘deuterium probe’ for the enantiomeric analysis of chiral amines, aminoacids and alcohols is proposed. The probe is the perdeuterated benzoyl fragment which can easily and reversibly be attached to the corresponding materials. The analysis is performed through measurements of the differential ordering effect (DOE) in the deuterium NMR of the chiral material dissolved in a cholesteric-nematic liquid crystalline system. Since all the chiral compounds which we studied were not racemic, the assignments of the observed DOEs to the enantiomers enabled us to draw tentative conclusions relating the results to the absolute configurations. This may open the way for the empirical derivation of absolute configurations of enantiomers from DOE measurements.

Conformational effects on ionization potentials: Photoelectron spectra of dibromo- and bromofluoro-alkyl compounds

Abstract The photoelectron spectra of 6 dibromoalkanes and 9 bromofluoroalkanes have been recorded in the region of 10 to 11 eV, corresponding to the ionization of the n electrons of the bromine atom. For most of the compounds four peaks are observed. In the dibromoalkanes these correspond to a spin-orbit coupling of the two bromine atoms. In the bromofluoroalkanes the peaks have been assigned to two different conformations of the molecule, each giving rise to a doublet. This study shows that differences in the ionization potentials may exist between preferential conformations of a molecule.

Flash vacuum pyrolysis of 1-methoxy-1,3-bis(trimethylsiloxy)-1,3-dienes: synthesis of α-allenic acids.

Abstract Flash vacuum pyrolysis at 680–700°C of 2- and 4- substituted 1-methoxy-1,3-bis (trimethylsiloxy)-1,3-butadienes yields α-allenic silyl esters which, upon hydrolysis, provide a direct route to α-allenic acids with good overall yield.

Flash pyrolysis: A route to “α-ketenic esters”.

Abstract 3-oxo 2-propenoic acid methyl ester has been prepared by flash vacuum pyrolysis and characterized by mass spectrometry and chemical trapping. Its four-membered cyclic dimers have been isolated.