Henri Strub

Solvatochromism of a typical merocyanine dye. A theoretical investigation through the CNDO/SCI method including solvation

Solvatochromism of a typical merocyanine dye is tentatively explained by a semi-empirical method including σ and π electrons (the CNDO/SCI method) for the first time. The procedure used makes allowance for a variation in geometry induced by the solvent, and stabilisation of the energy levels is introduced through the solvaton model proposed by Constanciel and Tapia. The calculations show that the solvatation results in a modification of the geometry from a ‘quinonoid’ to a ‘benzenoid’ structure with a concomitant general blue shift of the n→π* and π→π* transitions which fits the experimental results. Moreover, the results indicate a weak red shift of the π→π* transition for the lowest polarities. A detailed analysis of the composition of the π→π* transition made by considering the dipole moments of the ground and excited states substantiates the above-mentioned results. An attempt to explain the importance of the oscillator strength in the solvatochromism background and to correlate the net charges with the 13C shifts as the solvatation changes is proposed.

Determination of nicotine in allergenic extracts of tobacco leaf by high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) system has been developed for the determination of nicotine and cotinine in allergenic extracts of tobacco leaf. This analysis showed eight allergenic extracts of tobacco (leaf and Mix) to have markedly different nicotine patterns. Cotinine, a photodegradation product of nicotine, was not detected.

A new aspect of azo-hydrazone tautomerism

Abstract Structures of 3,5-dimethoxy-4-hydroxyazobenzene and of a new parent compound, 2,6-dimethoxy-4-hydroxyazobenzene, are investigated. Owing to their very high solubility it was possible to proceed to a comparison of the UV, 1 H NMR and 13 C NMR data for the same solvent. Symmetric substitution by two OMe groups in the ring bearing the OH group results in the isolation of the azo or hydrazone tautomer, using the available positions of substitution. The usefulness of the 13 C NMR technique in the investigation of azo-hydrazone tautomerism is underlined.

Unexpected formation of rearrangement and fragmentation products during the thermal activation of pyrazolino diazepines

Abstract Ionic and radical mechanistic steps are postulated in order to explain the formation of the rearrangement-, the isomerization- and the fragmentation-products isolated during the thermal treatment of pyrazolo-diazepines.

Electrocyclisation thermique disrotatoire d'anions a six electrons π derivant de dihydro-4,5 (1-H)-diazepines-1,2

Abstract Saponification of 1-ethoxycarbonyl and 1-benzoyl-4,5-dihydro (1-H) 1,2-diazepine derivatives leads, inter alia, to delocatized 6π electron anions which undergo thermal disrotatory electrocyclization to the corresponding bicyclic 4π anions. These latter ones are acetylated whereby stable diaza-2,3 bicyclo [3.2.0] hept-3-ene compounds are obtained.