Socikte suisse de chimie, Bale -Societa svizzera di chimica, Basilea Nachdruck verboten -Tous droits rCserv6s -Printed by Birkhauser AG., Basel On the regioselectivity of cycloaddition reactions of photochemically generated benzonitrile-isopropylides SummaryThis paper deals with the physical and chemical differences of zwitterionic benzonitrile-isopropylides, which differ by a p-substituent in the phenyl ring (H, F, OCH3;Scheme 2). These dipolar species (4-6) are produced by irradiation of the corresponding 2H-azirines (1-3; Scheme I ) in a 2-methylpentane glass at -185". Their UV. spectra are reproduced in the Figure. The spectra of 4 and 5 are characterized by an 'aromatic band' at short wavelength, and a longer wavelength band at approximately 275 nm, which is considered to be characteristic of the nitrile-ylide system. The UV. spectrum of the methoxy derivative 6, which shows a broad absorption at 260 nm, arises by an addition of the 'nitrile-ylide band' and the anisole band. The three dipolar species 4-6 do not show any significant differences in the regioselectivity of the cycloaddition with methyl a-methacrylate even though F and OCH3 have quite different 6-constants (Scheme I ) . The addition according to modus A is very much preferred (B/A = 0,076). -It seems, that the substituents F and OCH3 do not affect the physical and chemical behaviour of the parent benzonitrile-isopropyiide (4). All three dipolar species 4-6 react regjospecifically according to modus A with methyl trifluoroacetate (Scheme 3). The regioselectivity is reduced in the cycloaddition of 4 with methyl propiolate and ethyl phenylpropiolate (B/A = 0,04 and 0,28, respectively). The reduced regioselectivity in the latter case may be attributed to a reduced polarity of the triple bond in the dipolarophile.

In the language classroom, most lessons about English literature tend to concentrate on the pupils' analytical faculties. This article describes one of the standard approaches and discusses its advantages and deficiencies. I then introduce a different language activity which I think appeals to the whole personality of the pupil. The response called for is analytical as well as emotional. It is a learner-oriented activity without any direct interference by the teacher. The evidence in the tapescript of a lesson shows that the activity is particularly suited for fluency practice

Rearrangements of the Phenylthio Group of Trimethylsilyl‐enolethers of α,α‐Dialkylated α‐Phenylthio‐ketones Trimethylsilyl‐enolethers of α,α‐dialkylated α‐phenylthio‐ketones undergo a photochemically induced 1,3‐phenylthio shift leading to isomeric enolethers in high yields. The rearrangement can also be carried out under thermal conditions, but the results are less satisfying.

Die spezifische Alkylierung der α‐Phenylmercaptoketone (I) führt zu den Ketonen (II), die mit Trifluormethansulfonsäuretrimethylsilylester die Enolether (III) liefern.

Numerous kinds ofˆngerprint powder such as aluminum ‰ake have been successfully used for latentˆngerprint detection in crime scene investigation. Thesê ngerprint powders are hazardous to human health, especially for crime scene investigators, and sometimes seriously damage valuable furniture, electronic devices and precision instruments.In this paper, dogtooth violet starch, wheat ‰our, black tea, green tea, green laver were ground intoˆne particles less than 80 micrometers using a ball mill grinder. The shape of theseˆne powders were observed by scanning electron microscope (SEM), and their adherence to the skin ridge deposits was evaluated. Each powder detected a latentˆngerprint 4 hours after imprinting on a glass plate, but they did not give good results for older or weakerˆngerprints.Green laver, which is a marine plant of the green algae family, has a single cell layer structure. An improved green laver powder, produced by freeze-drying followed by grinding, contains a remarkable amount of thin plate particles. This characteristic feature of the improved green laver powder made it more adhesive, revealing even weak latentˆngerprints 3 days after imprinting on a glass plate. The quality of liftedˆngerprints was good enough to be used forˆngerprint identiˆcation.