Electronic densities and valence bond wave functions.

Valence bond (VB) wave functions are studied from the density point of view. The density is plotted as a difference with the quasi-state built on the same orbitals. The densities of the components of the VB wave function are also shown. The breathing orbital effect leads to small modifications of the density. It is shown that while the densities of ionic and covalent components are the same, their coupling ends-up in modifications of the electronic density.

Theoretical study of intramolecular aldol condensation of 1, 6-diketones: trimethylsilyl substituent effect

Diastereoselective intramolecular aldol condensations are investigated in an experimental and computational study of 1, 6-diketones. Ab initio results show the importance of the acid medium and disapprove the possibility of a spontaneous cyclization, even for silylated compounds. The combination of both experimental and computational approaches brings valuable information on the mechanism and on the selectivity of the aldol reaction. It is found that the enolization of the diketone is a key step in acid-catalyzed mechanism. The cyclization step bears a very small activation energy. The dehydration of the aldols are discussed.

Substituent effects on two-center three-electron bonds and hydrogen bonds involving unsaturated organic functional groups and an ammonia radical cation--the resonance contribution

A theoretical investigation of the substituent effects on the two-center, three-electron (2c-3e) bond involved between unsaturated functional groups and an amine nitrogen is presented. The competitive hydrogen-bonded complexes are also studied. In both cases, the bond energies are found to be in the range of 20-30 kcal mol(-1). The variation of these energies is discussed with respect to the electron-donating effect of the substitutents, as well as with respect to the alpha-bonded atom of the organic functional group (O, S, NH). For the 2c-3e bonds, the results are discussed on the basis of the differences of the ionization potential (delta IP) of the separated fragments and can be rationalized through the valence bond theory. For the hydrogen bonds, the substituent influence is discussed by using the differences of the proton affinities (delta PA) of the substrates. The resonating nature of the hydrogen bond in these cationic systems is investigated and is found to account for most of the binding energy. Marcus theory is compared with the proposed resonating model.

Diastereoselective tandem addition-cyclization reactions of unsaturated tertiary amines initiated by photochemical electron transfer (PET).

Polycyclic molecules and tetrahydroquinoleines were obtained in a tandem reaction involving the diastereoselective addition of alpha-aminoalkyl radicals to (5R)-5-menthyloxy-2[5H]-furanone 1. The facial diastereoselectivity on 1 is >/=90%. The alpha-aminoalkyl radicals were produced from tertiary amines by photochemical-induced electron transfer. When N,N-dialkylanilines 19 were used as starting tertiary amines, a rearomatization step was involved and important side reactions of 1 were observed. A mechanistic study involving isotopic labeling of the starting amine indicated that the byproducts resulted from reduction of 1 during the rearomatization process. An efficient optimization of the reaction was obtained by simply adding acetone or cyclopentanone as mild oxidants to the reaction mixture. The side products resulting from reduction of the furanone 1 were completely suppressed under these conditions, and the yields of the tetrahydroquinolines 21a-i, 22a-f, and 26g-i were doubled.

[The evaluation of prescribing practice in a general internal medicine outpatient clinic with special reference to gastrointestinal medicines]. / Die Evaluation der Verordnungspraxis in einem allgemeininternistischen Ambulatorium unter besonderer Berücksichtigung gastrointestinal wirksamer Medikamente.

Prescribing patterns of 13 residents in a medical outpatient clinic were evaluated between March and June 1986. Prescribed drugs influencing the gastrointestinal tract were also analyzed in order to define quality of the therapeutic process. Advertising for these special drugs in 3 Swiss medical journals was analyzed and compared with the prescribing behavior of participating physicians. 6300 patients with 3346 prescriptions (0.5 prescription/patient) were enrolled in the study. 16.5% of all prescriptions involved cardiovascular, 13.5% gastrointestinal, 9.5% non steroidal antirheumatic, 9.1% analgesic, 7.7% psychotropic and 7.4% antibiotic drugs. The share of 14 other classes of drugs was less than 4%. 471 prescriptions of gastrointestinal acting drugs were distributed over 288 patients (0.6 prescription/patient). 160 patients had irritable bowel syndrome, 40 ulcer disease, 23 inflammatory/infectious bowel disease, 18 gastroesophageal reflux, 18 anal diseases, 11 other gastrointestinal disorders and 15 were treated without diagnosis. Distribution of drugs was as follows: 27.5% bulk laxatives, 26% antacids, 15.7% H2-receptor antagonists, 13.5% anticholinergic agents, 4.9% laxatives, 3.4% loperamide, 9% other drugs. There was an increase in prescriptions per visit from 0.8 in 1980 to 1.5 in 1986. No important influence of drug advertising in 3 different medical journals published between January and June 1986 could be found. Considering the documented diagnoses, the therapeutic decisions were correct in 95.5% of cases treated. In conclusion, drug prescribing habits are permissive, the therapeutic approach is acceptable and the influence of drug advertising is negligible.