The groups related to the smallest non-affine Hall triple system

Every HTS is associated with a M₃-loop, just as every affine space overF ₃ is associated with an elementary abelian 3-group. If E is a M₃-loop, denote by(E) the corresponding HTS. Then ¦ Aut (E) ¦=¦E¦.¦Aut E ¦. When E is free among the M₃-loops which are nilpotent of class 2, the groups Aut E and Aut (E) may be described. The Fischer groups related to the non-affine HTS of order 3⁴ are described and the structure of their automorphism groups is discussed.     

Synthesis of ethyl 2-aminodihydro-5-pyrimidinecar-boxylate derivatives and 3,7-diethoxycarbonyl-4,6-dihydro-2,4,6,8-tetraaryl-1H-pyrimido[1,2-a]pyrimidines

Reactions of ethyl 3-aryl-2-benzoylpropenoates 1 with guanidine and N-alkyl(or benzyl)guanidines have been investigated. Ethyl 2-aminodihydro-5-pyrimidinecarboxylate derivatives 3, 4 or 5, and 3,7-diethoxy-carbonyl-4,6-dihydro-2,4,6,8-tetraaryl-1H-pyrimido[1,2-a]pyrimidines 6 have been synthesized.     

Cut-elimination and interpolation for Ω-logic

In 1978, Girard introduced-logic to generalize-logic. The basic category of-logic is the categoryON of ordinals. For geometric structure reasons, Girard changed the basic categoryON into the more general categoryWF of well-founded orders (1983). The logic he obtained was called-logic. Here, we extend (unpublished) results of-logic to-logic.     

Synthesis of some 2,4-disubstituted tetrahydropyrimido[4,5-b]quinolines as potential antitumor agents

Cyclocondensations of two 2,4-disubstituted 6-aminopyrimidines with 2-chloro-1-cyclohexenecarboxaldehyde afforded in each case a new regiospecific synthesis of tricyclic, linear disubstituted 6,7,8,9-tetrahydro-pyrimido[4,5-b]quinolines 2 and 3 in excellent yields. The linear structures and hence the regiospecificity of the synthesis were established using ¹H nmr and ¹³C nmr. The growth of leukemia L1210 cells in culture was inhibited 50% by 2 at 30 × 10^?6M and 48% by 3 at 100 × 10^?6M.     

Double nucleophilic addition of bis(trimethylsilyl)ketene acetals to carbon-carbon double bonds of pyrazines: formation of polycyclic γ-lactones

The double activation of pyrazines upon their interaction with methyl chloroformate leading in the presence of bis(TMS)ketene acetals to polycyclic N-containing γ-lactones parallels the interaction of the same ketene acetals with metal-activated aromatics. The fundamental role of the two oxygen-silicon bonds is outlined. This result broadens the scope of application of these ketene acetals as potential 1,3-dinucleophiles.     

Geometries of excited states of small polyenes

The behaviour under rotations around one or two double bonds of the first () singlet and triplet states of small conjugated molecules have been investigated using localized Molecular Orbitals. The results obtained with a ( + ) excitonic matrix are in agreement with previous results obtained with delocalized Molecular Orbitals: 1. the rotation around one double bond is more favorable than two symmetrical rotations around two double bonds, 2. the rotation occurs around one inner double bond rather than around a terminal bond. This work shows the role played by the ( — ) mixing in the stabilization of the twisted conformations. A further optimization of the bond lengths in the excited singlet and triplet states of butadiene shows that the preferred geometry is a non symmetrical twisted geometry with different lengths for the two C=C double bonds. This symmetry instability suggests to introduce a vibronic wave-function in which the various locally excited electronic wave functions are multiplied by different vibrational wave functions corresponding to local deformations of the nuclear skeleton.     

The influence of vibronic interactions on the chiroptical spectra of dissymmetric pseudo tetragonal metal complexes

The influence of vibronic interactions on the chiroptical spectra associated with a threesome of nearly degenerate electronic excited states in a dissymmetric molecular system is examined on a formal theoretical model. The model considers two vibrational modes to be effective in promoting pseudo Jahn-Teller (PJT) type interactions between the three closely spaced electronic excited states. Formal expressions are developed for the rotatory strengths of individual vibronic levels derived from the coupled electronic states. Two mode (vibrational)-three state (electronic) vibronic Hamiltonians are constructed (basis set size, 63–108, depending upon interaction parameters used) and diagonalized for a large number of different parameter sets representative of various vibronic coupling strengths, electronic energy level spacings, oscillator (vibrational mode) frequencies, and electronic rotatory strengths. Diagonalization of these vibronic Hamiltonians yields vibronic wave functions and energies which are then used to calculate rotatory strength spectra for the model system. The calculated results demonstrate the profound influence which vibronic interactions of the PJT type may have on the sign patterns and intensity distributions within the rotatory strength spectrum associated with a set of nearly degenerate electronic states. The implication of these results for the interpretation of circular dichroism spectra of chiral transition metal complexes with pseudo tetragonal symmetry are discussed.     

Synthese stereoselective d'esters α,β- ethyleniques α-methyles Z ou E par la reaction de wittig-horner a partir de phosphonates ou d'oxydes de phosphine

The reaction of α-branched aldehydes with diethyl 1-carbomethoxyethyl phosphonate 1b in THF/nBuLi at low temperature leads stereoselectively to Z α-methyl α,β-unsaturated esters. From a linear aldehyde, the reaction is less stereoselective, while from α,β-unsaturated ones, the E isomers are predominantly formed in good yields. From diphenyl 1-carbomethoxyethyl phosphine oxide 2b, E α-methyl α,β-unsaturated esters are stereoselectively formed either in DMF/tBuOK or in phase transfer conditions, whatever the starting aldehyde is, also in good yields. This reagent can thus advantageously replace the corresponding P-ylid. In all cases, the reaction conditions are determined so that by-products formation is minimized.     

On the mechanism of photoinduced nucleation in a diffusion cloud chamber

Photoinduced nucleation of NO₂ in supersaturated nonane has been studied in a diffusion cloud chamber. The photonucleation spectrum is found to correlate with the yield spectrum for the production of reactive radical species (O + NO) and not with the absorption spectrum of the nucleation inducing agent. A mechanism is proposed in which hydrogen abstraction by O from the nonane produces radicals which then react with each other or with NO₂ to produce species of low volatility that lead to nucleation. Studies of photoinduced nucleation by several alkyl iodides (known to produce radicals upon UV absorption) further support the proposed radical mechanism for photoinduced nucleation.