Chiral induction in photochemical reactions. 14. : Linear free energy relationships as an instrument for the prediction of either de values or conformation energies of the auxiliary in the diastereoselective Paternò-Büchi reaction.

To value a stoichometric asymmetric synthesis it is important for a synthetic chemist to gain information about those structural elements of a chiral auxiliary which are responsible for high diastertomeric excesses in a particular reaction. Furtheron it is desirable to have detailed knowledge about the mechanism of the chirality transfer. In this paper an empirical relation is formulated for the correlation of structural variations of a chiral auxiliary and its influence of the diastereomeric excess in the photochemical oxetane formation in correspondance to the Ugi/Ruch concept. For this purpose we use a Linear Free Energy Relationship (LFER) which we have adjusted to reaction (2) in order to obtain quantitative information about the selectivity of this reaction on the basis of special parameters of the auxiliary applied.     

Die photooxidation von chlorid zu chlor mit anthrachinonderivaten in wässriger lösung : Ein beitrag zur speicherung von sonnenenergie als chemische energie

Chloride transfers an electron to photochemically excited anthraquinonesulfonic and -methanosulfonic acid in its triplet state. In presence of oxygen the obtained semiquinone radical of the anthraquinonederivative is oxidized to the ground state anthraquinone, ready for another reactioncycle. The chloride is oxidized to chlorine. The quantum yield of this photooxidation, which also proceeds in sunlight, is found to be between 0.1 and 0.13. The absorbed light energy is partly stored in chemical energy of the chlorine molecule. The quantum yield is compared to the anthraquinone phosphorescence emission and the lifetime of the triplet state.     

Novel electronic transitions within excited doublets of dimers

We consider the electronic transition between the split components of the excited electronic doublet of a dimer species when the monomer species have permanent dipole moments. We show that the transition moment is given in terms of the permanent dipole moments of the ground and excited states of the monomers. Extension to ionic dimers and transitions between exciton bands in molecular crystals are suggested.     

The Isoinversion Principle—a General Model of Chemical Selectivity

A large number of successful methods for chirality transfer, using either stoichiometric or catalytic chiral auxiliaries, are in use today. However, there is a lack of practical and dynamic selectivity models, i.e. models which take into account the entire reaction sequence, and which allow simple and reliable assessment, optimization and prediction of selectivity in asymmetric syntheses. The models that are available are either too strongly biased to the steric requirement of the particular molecules reacting, but do not go beyond classical considerations of static facial differentiation, or they take a demanding, theoretical approach, which because of its inherent limitations and the great theoretical effort required has not yet found its way into the practical world of the synthetic chemist. The “Isoinversion Principle”, developed on the basis of Eyring's theory, closes this gap. With its aid, the synthetic chemist can determine the characteristic isoinversion temperature T_i for the reaction type of interest from a few temperature-dependent measurements of selectivity parameters. T_i then affords information on interesting questions such as optimization etc. The advantage of this method is that it is useful not only for stereoselectivity, but for any kind of process where selectivity in general (regio-,chemo-, etc) is generated at two or more stages of a reaction sequence, regardless of whether these reactions involve the ground state or a diabatic photoprocess. The present review will demonstrate that this generation of selectivity at two or more stages of a reaction sequence occurs more commonly than is generally thought.     

On the relation between classical and quantum statistical mechanics

Classical and quantum statistical mechanics are compared in the high temperature limit =1/kT0. While this limit is rather trivial for spin systems, we obtain some rigorous results which suggest (and sometimes prove) different asymptotics for continuous systems, depending on the behaviour of the two-body potential for small distances: the difference between suitable classical and quantum variables vanishes as ² for smooth potentials and as for potentials with hard cores.Supported in part by FAPESP. Permanent address: Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, Brazil     

Chemical composition and evaluation of the antimicrobial activity of the essential oil from leaves of Eugenia platysema

This study describes the qualitative and quantitative chemical composition and evaluates the antibacterial activity of essential oil from Eugenia platysema leaves. Analysis by GC–FID and GC–MS allowed the identification of 22 compounds. Different from the other species of the Eugenia genus, the major compound found in the essential oil was the diterpene phytol (66.05%), being this the first report of the presence of this compound in the essential oils from Eugenia genus. The sesquiterpene elixene was the second most concentrated compound in the studied essential oil (9.16%). The essential oil from E. platysema was tested for its antibacterial activity against cell-walled bacteria and mollicute strains of clinical interest using the microdilution broth assay. The results showed that the essential oil of E. platysema was inactive until 1000 μg mL^?1 against tested bacteria.     

Loudness reduction and adaptation induced by a contralateral tone

An intermittent tone in one ear may induce a large decline in the loudness of a continuous tone in the contralateral ear [Botte et al., J. Acoust. Soc. Am. 72, 727-739 (1982)]. To uncover the basis for this induced loudness adaptation, the method of successive magnitude estimations was used to measure the loudness of a test tone in one ear during and after a single presentation of a brief inducer tone in the contralateral ear. Duration and frequency of the inducer were varied. The frequency of the test tone was set at 500, 1000, or 3000 Hz. Both inducer and test tones were at 60 dB SPL. When the inducer lasted 5 s or more and was at the same frequency as the test tone, the loudness of the test tone was reduced by 80% to 100% while the inducer was on. As the inducer frequency moved away from the test tone, the loudness reduction declined gradually except for a more marked drop at the point where the frequency separation exceeded the critical bandwidth. Loudness remained depressed after the inducer went off. Additional measurements showed that the amount of loudness reduction corresponded closely to the measured movement of the inducer's sound image away from the center of the listener's head (decentralization).     

[Bis(2,4-dimethyl-6-tert.butyl-phenyl)ketone]chromium tricarbonyl—Stable torsional isomers

Complexation of bis(2,4-dimethyl-6-tert.butyl)ketone with chromium hexacarbonyl yields a mixture of two diastereomeric mono complexes in a ratio of 5 : 1. They can be separated by chromatography on silica gel at room temperature thus representing stable torsional isomers (isolable residual diastereomers).Dedicated to Prof. Dr.A. Neckel with cordial wishes on the occasion of the 60th anniversary of his birthday.