A simple route to 3-(dihalomethylene)cyclo-alkenes

Thermolysis of a number of bicyclic trihalocyclopropanes (1; X, Y = halogen) in the presence of quinoline leads either to 3-(dihalomethylene)cyclo-alkenes (8,9,10) with loss of halogen X $\text{or}$ to ring expanded 1,2-dihalocycloalka-1,3-dienes (11,13) with loss of halogen Y, depending on ring size and on the nature of the halogen.     

Media selection by mean-variance analysis

This note reports on an application of a recently developed mean-variance approach to media scheduling problems. The findings illustrate the effect of recognizing schedule variance in formulating candidate media plans, and demonstrate that mean-variance analysis is an effective approach to schedule formulation and assessment through parametric risk-return and budget-return analysis.     

Production of MeV antiprotons

In view of a future antihydrogen programme at CERN, the options for producing MeV antiprotons are revisited. The current limitations, operational performances and foreseen improvements are detailed. An alternative scheme using a dedicated machine for production and deceleration is also discussed.     

A molecular orbital approach to electronegativity equalization

From the basic premises of Molecular orbital theory it is shown that the various electronegativity equalization theories, at present in the literature, are fundamentally the same, and are expressable in a unified theory, developed herein. General relationships are established for calculating equilibrated electronegativities, electron densities and extra ionic resonance energies. The Equalization method is related to other methods for calculating the properties of localized bonds in molecules.

---

Zusammenfassung Auf der Grundlage der MO-Theorie werden die verschiedenen bekannten Theorien des ElektronegativitÄtsausgleichs im Rahmen einer Theorie dargestellt. Allgemeine Regeln zur Berechnung ausgeglichener ElektronegativitÄten, Elektronendichten und der zusÄtzlichen ionischen Resonanzenergien werden angegeben. Die Methode des ElektronegativitÄtsausgleichs wird mit anderen Methoden zur Berechnung der Eigenschaften lokalisierter Bindungen in Molekülen verknüpft.

---

Résumé On montre, à partir des fondements de la théorie des orbitales moléculaires, que les diverses théories d'égalisation de l'électronégativité, qui ont actuellement cours, sont essentiellement les mÊmes et peuvent Être exprimées dans une théorie unifiée développée ci-après. Des relations générales sont établies pour calculer les électronégativités égalisées, les densités électroniques et oes énergies de résonance ionique supplémentaires. La méthode d'égalisation est reliée aux autres méthodes de calcul des propriétés des liaisons localisées dans les molécules.

     

Prenatal screening and the reduction of birth defects in populations

OBJECTIVES: Birth defects occur in populations in 3-5% of births. This paper assesses whether population-wide screening programmes for pregnant women would be likely to result in major decreases in the prevalence of birth defects. METHOD: Relevant literature on this question is reviewed and synthesized. RESULTS: Given certain assumptions, a decrease from 3-5 to 2-4% in the prevalence of defects at birth may be possible. The resources required to put in place an appropriately delivered programme to achieve this are substantial. CONCLUSIONS: As well as the potential benefit of a decrease, there are opportunity costs, and potential serious harms. Unless undertaken in a carefully planned and monitored way, a population-based birth defects reduction programme is likely to bring harm and anxiety rather than benefit.     

Stable ion study of benzo[a]pyrene (BaP) derivatives: 7,8-dihydro-BaP, 9,10-dihydro-BaP and its 6-halo derivatives, 1- and 3-methoxy-9,10-dihydro-BaP-7(8H)-one,as well as the proximate carcinogen BaP 7,8-dihydrodiol and its dibenzoate,combined with a comparative DNA binding study of regioisomeric (1-, 4-, 2-) pyrenylcarbinols

A stable ion study of a series of BaP derivatives is reported. 7,8-Dihydro-BaP 1 gives a persistent bay-region benzyliclike carbocation which shows extensive charge delocalization into the pyrene moiety. In contrast, a "benzylic" carbocation can not be generated from 9,10-dihydro-BaP 2. Introduction of bulky substituents at peri C-6 of 9,10-dihydro-BaP (as in 4 and 5) prevents side reactions (dimerization) to the extent that the initially formed carbocation undergoes rearrangement to generate the corresponding bay-region "benzylic" carbocation as a persistent species. Introduction of methoxy substituents into the 1- or 3-positions of 9,10-dihydro-BaP-7(8H)-one (6,7) increases its electrophilic reactivity to the extent that stable carboxonium-arenium dications are produced in FSO3H-SO2ClF. A detailed NMR study (at 500 MHz) of the resulting mono- and dications is reported, and charge delocalization mode (as well as conformational aspects) are addressed. Other oxidized derivatives of BaP such as the 7,8-dihydrodiol 9 and the 7,8-dihydrodibenzoate 8 are not suitable models for stable ion study because of competing O-protonation (and elimination). Energies for various possible arenium ions and regioisomeric "benzylic" cations were computed by the DFT method at the B3LYP/6-31G(d)//B3LYP/6-31G(d) level or by AM1 for comparison with the experimental results. These findings provide further evidence in support of the stability sequence: 1-pyrenyl > 4-pyrenyl > 2-pyrenyl in alpha-pyrene-substituted carbocations as models for the intermediates arising from BaP-epoxide ring opening. In an effort to provide a parallel, a series of alpha-pyrenylcarbinols were subjected to a DNA binding study using human MCF-7 cells. The results/trends are discussed and compared with the stable ion data.     

Group orbital electronegativities

The Self-consistent Group Orbital and Bond Electronegativity (SGOBE) method [4] for calculating the orbital charge distributions in polyatomic molecules is reviewed, and a simplification described. The charge distributions for several polyatomic molecules are calculated. The chemical significance of the results is discussed.

---

Zusammenfassung Es wird ein Überblick über die SGOBE-Methode zur Berechnung von Ladungsverteilun-gen in Molekülen gegeben und eine Vereinfachung dazu beschrieben. Die Ladungsverteilung einiger mehratomiger Moleküle wird berechnet und die chemische Bedeutung diskutiert.

---

Résumé La méthode auto-cohérente des orbitaux de groupe et électronégativités des liaisons (SGOBE) pour calculer la distribution de charge orbitale des atomes dans les molécules poly-atomiques est résumée, et une simplification de la méthode SGOBE est décrite. Les distributions de charge de plusieurs molécules polyatomiques sont calculées, et la signification des résultats est discutée.