Synthesis of 6R(β)-tritylaminopenicillanic-3R(β)-alcohol,a versatile stereoisomer of natural β-lactams

In an attempt to rationalize a synthesis of penicillin analogs modified at C(3), we have isolated the 3R(β)-carbinolamide derivative 4a. The trityl substituent on N(6′) seems to be responsible for the inversion of configuration which occurs at C(3) during the acid hydrolysis of the isocyanate intermediate. An hydrogen bond is formed on the β-face of the bell-shaped bicyclic skeleton between the N(6′)-nitrogen lone pair and the C(3) hydroxyl group. On standing, the carbinolamide analog slowly isomerizes to its expanded bicyclic isomer 4b , but the starting material may be easily recovered by treatment with acid. The postulated intermediate during isomerization, i.e., the open aldehyde form, does not accumulate. Substitutions of the hydroxyl group at C(3) lead to a variety of compounds with the biologically active 3S(α) configuration. These may be used to study the importance of the carboxyl group of penicillins in their interaction with β-lactamases at the molecular level.     

The effect of the t-butyl substituent on polymer properties in homopolymer systems

The effect of a bulky substituent on properties of different homopolymers has been examined. The substituent is the t-butyl moiety attached to a benzene ring found in the repeat units of the homopolymers of polyesters, polyarylates, polyamides, and polyaramides. These polymers have been prepared by melt, solution, or interfacial techniques. The source of the t-butyl group is mainly from 5-t-butylisophthalic acid (5TBIA) and comparisons are generally made with corresponding homopolymers based on isophthalic acid. The effect of the t-butyl group is shown by comparison of the properties of these homopolymers. Thermal and mechanical (tensile and impact) properties, density, water absorption, solubility, and processability are discussed. Differences in these properties are attributed to the t-butyl group and are based on intermolecular and intramolecular interactions that include increased free volume, chain stiffening, and conformational changes.     

Growth transition and morphology change in polypropylene

The growth rate of isotactic polypropylene is deduced from microscopic observations during isothermal crystallizations. A change in the growth regime is observed at 138 C and interpreted as a Regime III Regime II transition, according to Hoffman's kinetic theory of polymer crystallization. A Regime II Regime I transition is also theoretically predicted at 155 C, i. e. at a temperature outside the investigated temperature range. The Regime III Regime II transition is related to the positive to negative change in the spherulite birefringence, which is generally attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae atT _c < 138 C (Regime III) and preferentially radiating lamellae atT _c > 138 C (Regime II). It is suggested that such a morphological change could be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. This interpretation could also explain the interspherulitic ruptures observed in negative spherulites.     

Etude d'un modele d'induction asymetrique: Les oxazolidines α,β-insaturees issues de l'ephedrine

Various oxazolidines were prepared from ephedrine. It was shown that their formation is not general, the reaction is not always stereoselective and can lead to isomerization of the double bond of α,β-unsaturated aldehydes. Some of these oxazolidines were used in stereoselective preparation of β-alkyl aldehydes.     

Benzophenone photoreduction by heteroatom-containing donors

Nanosecond flash photolysis has been carried out on benzophenone solutions in benzene and acetonitrile in presence of oxygen- and sulfur-containing reductants such as anisole, thioanisole, dibutyl sulfide and methyl 2-octyl ether. The quantum yield of ketyl formation is compared to previous results on the quantum yields of the final benzophenone disappearance. This comparison is also related to previous data on benzophenone reduction by nitrogen-containing reductants such as amines and amides and suggests a general mechanism for benzophenone photoreduction by heteroatom-containing donors.     

Halogenation of isoflavones using thionyl and sulphuryl chlorides

The reactions of thionyl and sulphuryl chlorides on isoflavones have been found to give a number of new chloroisoflavones and isoflavanones, whose structures have been elucidated on the basis of their spectral analytical data.     

Wave mechanics - the first fifty years : edited by W.C. Price,S.S. Chissick and T. Ravensdale,Butterworths, London, 1973, pp. 435, price £12.00

The free NH₃ molecule and the [Zn(NH₃)₄]²⁺ ion were studied by the kinematic coupling approach. The pure effects of this coupling were found to be small, and some modifications had to be introduced in order to get a reasonable force field. The force constants deduced for the skeletal vibrations are comparable with those of a quasi-exact force field. Calculated frequencies for [⁶⁸Zn(NH₃)₄]²⁺ and [⁶⁴Zn(ND₃)₄]²⁺ are reported in addition to those of [⁶⁴Zn(NH₃)₄]²⁺. Mean amplitudes of vibration for [⁶⁴Zn(NH₃)₄]²⁺ are given.     

Determination of aflatoxins in peanut products using reverse phase HPLC

A high performance liquid chromatographic (HPLC) method is described for the determination of the four major aflatoxins, B1, B2, G1 and G2, in peanut products. The aflatoxins are extracted by adapting a procedure developed by Pons (1) at the SRRC, USDA, and quantitated utilizing a new 5 mum reverse-phase column with NaCl/acetontrile/methanol mobile phase (3 + 1 + 1). The 5 mum column achieved baseline resolution of each of the four aflatoxins. Retention times and peak heights were reproducible. The procedure was successfully applied to several types of peanut products and was applicable to both roasted and unroasted peanuts, which is a decided advantage over the current CB and BF extraction methods. Additionally, it can be used for sweetened peanut matrixes with no interferences in the chromatography. The total time required for sample preparation and aflatoxin determination is less than 1.5 hours.     

Thermal decomposition of copolymers of styrene and halogenated monomers

Copolymers of 1,2,2,2-tetrachloroethyl esters of unsaturated acids and halogenated N-phenyl maleimides with styrene were pyrolyzed; volatile products were analyzed with a mass spectrometer combined with a gas chromatograph. Hydrogen halide and carbon dioxide in the volatile products were determined during the thermal decomposition of copolymers in glass ampoules; the acyl chloride groups were determined in the residues. The thermal decomposition of copolymers of tetrachloroethyl esters with styrene sets in at ca. 230° by the release of chloral from the copolymer and splitting of some of the CCl bonds in the copolymer. The decomposition of copolymers of styrene with halogenated N-phenyl maleimides starts above 300° by depolymerization of the polystyrene chain sections and by splitting of some of the carbon-halogen bonds. At 310 and 500° for copolymers of tetrachloroethyl esters and at 500° for halogenated N-phenyl maleimides, there is radical dehydrohalogenation of the copolymers, with depolymerization of polystyrene blocks and splitting of carbon-carbon bonds in the main chain.     

Intramolecular metal—double bond interactions : VII. Intramolecular cyclization of alkenyl derivatives of lithium,aluminum, gallium and indium

The intramolecular cyclization reactions of tri-1-hex-5-enyl Group III derivatives and of 1-hex-5-enyllithium have been investigated and it is proposed that the reactions may be depicted as internal addition across the terminal double bonds of the alkenyl species. The cyclization reaction proceeds more readily for the 1-hex-5-enyl derivatives than for any other chain length and is dependent on temperature, concentration and solvent. ¹H NMR data and cryoscopic molecular weight data are presented for several diisobutyialkenyl- and diisobutylalkyl-aluminum derivatives. These data have been interpreted in terms of a direct intramolecular interaction between the metal center and the π-electron system of the olefinic site. The intramolecular cyclization reactions for the 1-hept-6-enyl, 1-oct-7-enyl- and 1-undec-10-enylaluminum derivatives also were investigated and it was found that cyclization occurred only for the 1-hept-6-enyl derivative.