Substituted chromans and tetrahydrofuro[2,3-b]benzofurans (trapped tetrahedral intermediates) from 3-phenyl-2-benzofuranones

The previously discovered neighboring group reaction has been extended to the synthesis of chroman derivatives (i.e., 4, 5, 6) containing geminal methyls in the 2-position, a feature common to certain physiologically active natural chromans. In two instances, cyclic ortho ester by-products (8), not observed in previous work, were formed as a result of the intramolecular trapping of tetrahedral intermediates. Reasons for the incursion of this unexpected side reaction are discussed.     

Anomalous behaviour of the Landé factors and the chemical shift close to the dissociation limit of the B state of molecular iodine

Resonances in a modulated light beam have been observed on five transitions in the visible band system of I₂. Landé factors g_J and chemical shifts g₁ have been measured for levels very close to the dissociation limit of the B state.     

Electron-impact studies—LXX. Substituent effects in the negative-ion spectra of nitroaryl esters

The negative-ion mass spectra of a variety of substituted nitroaryl benzoates and aryl nitrobenzoates have been studied. Pronounced proximity effects are observed in the spectra of ortho-substituted compounds. The meta and para pairs fragment in a similar manner. Linear plots are observed for many cleavages using either the McLafferty or Harrison methods. Evidence is provided which suggests that the fragmentations of meta and para isomers may proceed by the same mechanistic pathway. The magnitude of ρ does not appear to provide precise information concerning the nature of the transition state for a particular reaction of a negative ion.     

Sizes and interfacial free energies of crystallites formed from fractionated linear polyethylene

Replicas of fracture surfaces of fractions of linear polyethylene, which were crystallized at elevated temperatures for extended time periods, were examined by electron microscopy. Striated. lamella-type crystallites were observed for all molecular weights over the range 3.2 × 10³?5.7 × 10⁵. In agreement with Anderson's previous report, for molecular weights of 12,000 or less, the crystallite thicknesses were comparable to the extended chain length. As the molecular weight increased above this level, however, the crystallite sizes increased only slightly and hence at high molecular weights were very much smaller than the extended chain length. From the measured melting temperatures, crystallite interfacial free energies were calculated from the theory for the melting of finite size crystals comprised of chains of finite length. The crystallite interfacial free energy was found to increase with molecular weight. Based on these results, a crystallization process is outlined which allows for the formation of either extended chain crystallites, or crystallites whose size is much smaller than the extended chain length without any change in nucleation mechanism or arbitrary adjustment in growth mechanism with molecular weight.     

Total synthesis of natural (levo) and enantiomeric (dextro) forms of prostaglandin El

1 newly-discovered method of synthesizing PGE1 (prostaglandin E1) is explained and diagrammed chemically. Recrystallization of the synthetic product produced material identical in all respects with natural PGE1. The synthetic product showed the same infrared spectrum and chromatographic values as racemic and natural forms of PGE1. The biological activity of the synthetic product was found to be .1% of that of the naturally-occurring PGE1 in the stimulation of smooth muscle contraction. This is the 1st report of a total synthesis of PGE1. Research continues on improvements in this synthesizing method and on discovering other synthetic approaches to PGs.     

High frequency titrations involving chelation with ethylenediaminetetra-acetic acid. II. quantitative determination of some divalent metals

The high frequency oscillator provides an excellent means of detecting the end-points of titrations performed with ethylenediaminetetraacetic acid or its salts. The determination of various divalent metals is reported, based on both direct and indirect titrations. Because of the great sensitivity of the method it is possible to determine cobalt, nickel, copper (II), zinc, cadmium, lead and manganese (II) in concentration ranges of 1/1000 to 1/6000M.     

Preparation and properties of cross-linked fluorescent poly(methyl methacrylate) latex colloids

We report a single step preparation of monodisperse fluorescent poly(methyl)methacrylate (PMMA) lattices cross-linked with ethylene glycol dimethacrylate with radii in the range 150-1000 nm using dispersion polymerization. The particles are applied as fluorescent cores in core-shell PMMA particles for confocal microscopy (Dullens et al. Langmuir 2003, 19, 5963). Contrary to un-cross-linked particles, these cross-linked colloids are stable in good solvents for PMMA as well. Therefore we studied the properties of the cross-linked PMMA particles in the good solvents tetrahydrofuran (THF), chloroform, and toluene using light scattering and confocal scanning laser microscopy. We show that the particles swell instantaneously and that their volume can increase up to more than seven times their volume in poor solvents. Further, it is very likely that the particles are charged in THF.     

Homoatomic P --> P coordination: a versatile synthetic approach to polyphosphorus dications

Polyphosphorus dications have been synthesised and comprehensively characterised as diphosphine (dppe, dmpe and dpph) linked Ar2P+ Lewis acids (Ar = C6H5); this application of unique homoatomic coordination chemistry provides important building blocks for extended systems.     

Numerical analysis of capillarity in packed spheres: planar hexagonal-packed spheres

General solutions of the capillary pressure for liquids as a function of contact angle and volume in planar close-packed spheres have been calculated numerically using Surface Evolver software. Applied pressure differences between liquid and vapor result in undulating (puckered) menisci exhibiting anticlastic curvature in the narrower spaces near particle contacts. The corresponding capillary pressures exhibit maxima with infiltration volume (minima with drainage), corresponding to critical pressures for engulfment of the spheres by the liquid (vapor). The analysis also reveals the formation of residual pendular rings of the wetting phase around particle contacts. Pendular ring formation is explored further by analyzing hexagonally packed spheres separated by 1/10 their radius. The results are discussed relative to the wide range of approximate solutions available in the literature.     

Cycloaddition of carbonyl compounds on Si(100): new mechanisms and approaches to selectivity for surface cycloaddition reactions

Density functional theory has been used to explore cycloaddition reactions of organic molecules containing carbonyl functional groups on the Si(100) surface. As with other pi bonds, carbonyl groups can add to the surface by a [2+2] cycloaddition with negligible activation barrier, as previously shown through experiment. However, the present calculations indicate that 1,2-dicarbonyls, such as glyoxal, may also react by means of a [4+2] addition to form a hetero-Diels-Alder product in which the organic ring stands normal to the surface. Calculations of [2+2] and [4+2] pathways indicate that both reactions proceed without significant barriers. This reactivity is analogous to that of conjugated dienes, in which evidence for both reactions has been observed. In contrast to unsaturated alkyl systems, which must react through the pi electron system, the reactions of carbonyls may proceed through a very different mechanism, in which the initial surface interaction is through the oxygen lone pair. The presence of lone pairs affects the geometry of the [4+2] adduct, and may alter the competition between [2+2] and [4+2] addition. Some potential rearrangement reactions of the initial binding products are described. Recent experimental studies of a 1,2-dicarbonyl on Si(100) are reinterpreted in light of these calculations, and found to be consistent with the presence of the [4+2] adduct. Finally, some molecules are suggested as cycloaddition reagents for experimental tests of the conclusions presented here.