Hypocholesterolemic agent compactin. an alternative diels-alder strategy for the synthesis of the hexahydronaphthalene portion

The synthesis of the hexahydronaphthalene segment (4) of compactin (1) has been accomplished in a short sequence (8 steps from 9) featuring the intramolecular Diels-Alder cycloaddition of 7b.     

Evidence of neutral impurity scattering in mercury sulphide (α-HgS) in the temperature range 77–300 K correlation with chemical analysis

Five natural or synthetic trigonal HgS single crystals have been studied by transport experiments in the temperature range 77–300 K. The classical d.c. technique has been used to measure the Hall coefficient and the resistivity. The temperature dependence of the free carrier density in the conduction band associated to a chemical analysis have brought to light the presence of neutral donor impurities with a density much larger than the ionized ones, which has led us to consider the existence of neutral impurity scattering even at room temperature.A detailed study of the mobility has shown that, among the four possible and efficient scattering processes, (neutral impurities, ionized impurities, acoustical phonons and optical polar modes), the most efficient in the whole experimental temperature range is the neutral impurities one. However, at room temperature, the polar optical mode becomes comparable to the previous one. The agreement obtained between the experimental values of the mobility and the calculated ones by taking into account these four scattering modes is very good in the whole temperature range.So for the first time an explanation is given for the rather low value of the mobility in mercury sulphide. This explanation of the mobility behaviour is in good agreement with the results of the chemical analysis which shows in HgS-α the presence of impurities very much larger than that of the ionized impurities one.     

Caps and codes

The packing problem in the theory of caps is that of finding, or at least bounding, the size m(r, q) of an ovaloid (cap of largest size) in the projective space S_r,q of dimension r over a field of q elements. This problem and that of constructing and classifying ovaloids are approached by consideration of certain codes associated with caps. Improved general upper bounds on m(r, q) are found, which give m(5, 3)?56 as a particular case. A 56-cap in S_5,3 is constructed via its code and its uniqueness as an ovaloid is demonstrated.     

Transferability of some properties of localized molecular orbitals

The localized molecular orbitals of some related ten- and eighteen-electron systems have been studied. The transferability of the kinetic, self-interaction, Coulomb and exchange interaction energies on localized orbitals have been shown. The standard deviation of the kinetic and of the interaction energies (including exchange) are less than 2.5% except for lone pair orbitals of the oxygen atoms where the standard deviation is close to 4%.     

Determination of substituent chemical shifts in the proton resonance spectra of the porphyrins

Reproducible proton chemical shifts in the porphyrin series are obtained when the spectrum is measured in chloroform using the zinc (II) complex of the porphyrin in the presence of an excess of pyrrolidine. This method is specifically demonstrated for the case of 2,4-dicyanodeuteroporphyrin-IX dimethyl ester which, as the free base, shows dramatic effects due to aggregation phenomena. The shifts obtained using the zinc (II) complex plus pyrrolidine method, which allow compilation of substituent chemical shifts in the porphyrin series, are shown to be the same as the less easily accessible infinite dilution shifts of the porphyrin free bases.     

The synthesis of some pyrrolo[1,5-b:2,3-c′]dipyridazines

A facile method for the preparation of the aromatic pyrrolo[1,5-b:2,3-c']dipyridazine ring system is reported. A number of compounds have been prepared and the biological screening data reported.     

Effects of pressure on optical F-bands in rubidium halides

High pressure optical absorption measurements have been made on additively colored RbCl and RbBr at pressures up to 10 kbar and on electrolytically colored Rbl up to 4 kbar. The pressure dependence of the F-band produced in RbCl by x-irradiation in the s.c. phase is also reported. Effects of the pressure induced structure transformation in these salts are described. F-band pressure shifts are related to a semi-empirical treatment which takes account of relative ion sizes. A new Ivey law for F-centers in host crystals having the s.c. structure is presented. This relation is established using all available F-band data including those for salts transformed to the s.c. structure by the application of high pressure.     

Swelling of crosslinked poly-4-vinylpyridine

Polyvinylpyridine of molecular weight 0.77 × 10⁶ was crosslinked by 2.5, 5, and 10% BrCH₂C₆H₄CO(CH₂)₈COC₆H₄CH₂Br and by 10% ClCH₂C₆H₄CH₂Cl; quaternization of the gel was completed with n-butyl bromide. Swelling ratios in aqueous solutions of lithium, sodium, and 4-isopropyl-N-n-butylpyridinium bromide and in methanolic lithium bromide were determined. Selectivity increased in the sequence Li⁺ <Na⁺ <PrN⁺?C₅H₅. The Flory parameter χ₁, which measures interaction between solvent and polymer, decreased from 1.5 kT to nearly zero with increasing density of crosslinks in the aqueous solutions, and from 3 kT to 0.5 kT in the methanol solutions. The inverse proportionality of q^2/3 (q = swelling ratio) to the crosslinking density was approximately verified for swelling of the resins in water, methanol, and dimethylformamide.