Stereochemical analysis of deuterated alkyl chains by MS/MS

Vicinally deuterated sec-alkyl phenyl ethers, CH(3)(CH(2))(m)()CH(OPh)CHD(CH(2))(n)()CH(3), display significant differences in mass spectra between threo and erythro stereoisomers. MS/MS experiments, in which parent ions of a single mass are selected and their fragmentation patterns subsequently measured, show that alkene expulsion represents virtually the only decomposition pathway. Two types of MS/MS experiment are reported: mass-analyzed ion kinetic energy (MIKE) spectroscopy of metastable ions and collisionally activated decomposition (CAD) of stable ions. The expulsion of a deuterated alkene from a monodeuterated precursor yields ionized phenol, PhOH(*)()(+) (m/z 94). The expulsion of an undeuterated alkene yields PhOD(*)()(+) (m/z 95). Without exception, the ratios (PhOD(*)()(+)/PhOH(*)()(+)) from precursors in the threo series have values greater than their diastereomers in the erythro series. The ratio of ratios, r = PhOD(*)()(+)/PhOH(*)()(+) for the threo divided by PhOD(*)()(+)/PhOH(*)()(+) for the erythro, has a value of 1.2 for the 2-phenoxy-3-deuteriobutanes and larger values for all of the higher homologues up through the monodeuterated phenoxyoctanes (m + n = 4). The highest degree of stereoselectivity, r = 5.8, is measured for 3-phenoxy-4-deuteriohexane. Experiments with multiply deuterated analogues show that alkene elimination is highly regioselective, unlike the corresponding decompositions of ionized sec-alcohols or their acetates. The fact that a large fraction of ionized sec-alkyl phenyl ethers undergo stereospecific syn-elimination means that mass spectrometry has a useful capacity to distinguish one isotopically labeled diastereomer from another.     

Synthesis of new polyfunctional 2-pyrrolidinones from methyl 2-(carboethoxyhydroxymethyl)acrylate

The synthesis of new polyfunctional 2-pyrrolidinone derivatives from methyl 2-(carboethoxyhydroxymethyl)acrylate is described. These alkenes present an extremely high reactivity upon Michael addition with primary amines leading to a simple, mild, and efficient route to the preparation of new polyfunctional pyrrolidinones.     

Preparation d'olefines trisubstituees bifonctionnelles par voie photochimique

∝-methyl ∝-functionalized (CO₂CH₃, CN, CH₂OH and CH₂Cl) cyclopentanones $\text{2}$ when irradiated by UV light give title compounds : 5-substituted 4-hexen 1-al $\text{4}$ as a mixture of E and Z isomers. A comparison of the photochemical behaviour of this cyclopentanones and a simple and efficient chemical transformation of the isomers Z in the more demanded isomers $\text{4}$ E are described.     

Impact of space-energy correlation on variable range hopping in a transistor

Hopping conduction in transistors, i.e., under a transverse electric field, is addressed using percolation theory with a space-energy correlation in the density of states of the impurity band. The computation of the percolation threshold over an extended range of correlation parameters enables us to derive a formula, which, while giving the classical results in the low field limit, describes the emergence of a specific variable range hopping in the high field case. An application of this formula to experimentally extract the localization radius is also proposed.     

Two connected inverse spectral transforms

We establish a transformation which connects the potentials of the one-dimensional Dirac and Klein-Gordon operators. This transformation links the solutions of the nonlinear evolution equations solvable by means of the two inverse spectral transforms which use the Dirac and Klein-Gordon direct and inverse spectral problems.     

Analogies Photochimiques. III—Diméthyl-4,4 allyl-2 Cyclohexanone. Elimination Inattendue de C2H4O et Perte de 15 Unités de Masse

The mass spectrum of 4,4-dimethyl 2-allyl cyclohexanone shows an ion at m/z 122 resulting from the elimination of a neutral acetaldehyde molecule direct from the molecular ion. Deuterium labelling results show a complex decomposition pathway during which four hydrogen atoms transfer to the eliminated acetaldehyde molecule. The molecular ion of this compounds also loses a methyl group originating from the allyl substituent. The mechanisms are discussed in terms of photochemical analogies.     

The Structure of 1H-Perimidin-2(3H)-one and Its Derivatives in the solid state (x-ray crystallography and CP/MAS 13C-NMR), in solution (13C-NMR), and in the gas phase (mass spectrometry)

The X-ray crystal and molecular structures of 1-methyl- 1H-perimidin-2(3H)-one ( 5b ) and 1,3-dimethyl-1H-perimidin-2(3H)-one ( 6 ) were determined. The crystals are built of piles of dimers faced head-to-head in 5b and of alternating independent head-to-tail molecules in 6 , both along the b axis. Semiempirical calculations at the AM 1 level revealed that the eclipsed conformation of the Me groups with respect to the C?O group, found in the crystals, is the most stable. The lack of planarity of the whole molecules is a consequence of the packing forces since it is not found in the calculations. A comparative NMR study was carried out in solution (¹H and ¹³C) and in the solid state (CP/MAS ¹³C) for 1H-perimidin-2(3H)-one ( 2 ) and 1H-benzimidazol-2(3H)-one ( 3 ) with the conclusion that in both heterocycles the oxo tautomer is the most abundant. The structure in the gas phase was approached by mass spectrometry. In the case of 3 , the oxo tautomer loses CO after ionization, while the oxo form of 2 tautomerizes to the hydroxy form which loses, H₂O after a [1,3]-H shift. AM 1 calculations were carried out on the ground and ionized states of 2 .