Réactions de cyclisation de pentynyl-2 pyrimidones-4

Acetylenic amindines HC≈?C·(CH₂)_n·C(?NH)NH₂ give, by condensation with β-ketoesters, pyrimidones substituted on carbon 2 by an acetylenic chain. Two types of evolution are observed when compounds are heated without any catalyst. The minor route is a cyclization by attack on a triple bond by the amidic nitrogen atom. The main reaction is a cycloaddition involving the non activated triple bond and an azadienic system, leading to non isolated tricyclic intermediates which retrocyclize to stable bicyclic compounds.     

Stability and bonding of disilyne and its isomers: A generalized valence bond-effective potential study

We have employed an effective potential and a single-zeta basis in SCF–MO computations to estimate the relative stability of linear disilyne HSiSiH and five isomeric structures defined in earlier all-electron ab initio SCF–MO computations. The effect of electron correlation has been estimated by generalized valence-bond (GVB ) computations for the five valence electron pairs of these structures. All our computations indicate that linear disilyne is the least stable structure and that H₂SiSi, the silicon analog of vinylidene carbene, is the most stable structure. In these structures silicon occurs in divalent and tetravalent states. The nature of silicon bonding in these valence states is illustrated by contour diagrams of the GVB orbital pairs.     

A new look at correlations in atomic and molecular systems. I. Application of fermion monte carlo variational method

We are engaged in research directed toward the development of compact and accurate correlation functions for many-electron systems. Our computational tool is the variational method in which the many-electron integrals are calculated by Monte Carlo using the fermion Metropolis sampling algorithm. That is, a many-fermion system is simulated by sampling the square of a correlated antisymmetric wave function. The principal advantage of the method is that interelectronic distance r_ij may be included directly in the wave function without adding significant computational complexity. In addition, other quantities of physical and theoretical interest such as electron correlation functions and representations of Coulomb and Fermi “holes” are very easily obtained. Preliminary results are reported for He, H₂, and Li₂.     

Finiteness results for lattices in certain Lie groups

In this note we establish some general finiteness results concerning lattices Γ in connected Lie groups G which possess certain “density” properties (see Moskowitz, M., On the density theorems of Borel and Furstenberg, Ark. Mat. 16 (1978), 11–27, and Moskowitz, M., Some results on automorphisms of bounded displacement and bounded cocycles, Monatsh. Math. 85 (1978), 323–336). For such groups we show that Γ always has finite index in its normalizer N _G (Γ). We then investigate analogous questions for the automorphism group Aut(G) proving, under appropriate conditions, that Stab_Aut(G)(Γ) is discrete. Finally we show, under appropriate conditions, that the subgroup \(\tilde{\Gamma}=\{i_{\gamma}:\gamma \in \Gamma \},\ i_{\gamma}(x)=\gamma x\gamma^{-1}\), of Aut(G) has finite index in Stab_Aut(G)(Γ). We test the limits of our results with various examples and counterexamples.     

Central idempotent measures on connected locally compact groups

A measure μ of finite total variation on a locally compact group G is idempotent if μ 1 μ = μ, and is central if invariant under all inner automorphisms of G. Recent results of D. Rider and D. Ragozin concerning compact groups are combined with results of the authors for noncompact groups to determine all central idempotent measures on a connected G in terms of the structural features of G.     

Valence band and Zn 3d energy levels in Me2Zn from photoelectron spectra and pseudopotential ab initio calculations: electric field gradients in gas phase Zn compounds

The He I and X-ray photoelectron spectra of the valence levels and Zn 3d levels in Me₂Zn have been recorded. The orbital ionization potentials are compared with those obtained from our ab initio pseudopotential calculation on Me₂Zn. There is excellent agreement between predicted and observed values for the outer valence orbitals. The Zn 3d level in Me₂Zn in split into five peaks due to the combined effect of spin-orbit splitting and crystal field splitting. The major part of the splitting is due to the asymmetric C⁰₂ crystal field term which transforms like the electric field gradient. The derived C⁰₂ terms for Me₂Zn and ZnCl₂ are ?0.0169 ± 0.0007 eV and ?0.011 eV respectively. The observed and calculated splitting confirms an electrostatic (rather than a bonding) origin. The C⁰₂ value for Me₂Zn is consistent with that observed recently for Me₂Cd.