Electronic and steric substituent effects on the fluorescence emission of 2-pyrazoline derivatives.

A series of substituted 2-pyrazolines were synthesized, and the steric and electronic effects of substituents on the C - and C -positions of the heterocyclic ring on their fluorescent ability were investigated. Two different conjugative intramolecular charge transfer (ICT) and intramolecular charge transfer through space (spiro-conjugation) affect the fluorescence intensity of these compounds. The extent of the ICT process and spiro-conjugation depends on the electronic nature of the additional substitution and its position on the attached aryl rings.

Photooxidation of 2,3-dihydroquinazolin-4(1H)-ones: retention or elimination of 2-substitution.

A series of mono and disubstituted 2,3-dihydroquinazolin-4(1H)-ones (DHQZs) were synthesized and the electronic and steric effects of the C- and N-substitutions on the retention or elimination of the C-substitution by exposing them to the ultraviolet light were investigated. Electron transfer from photo-excited dihydroquinazolinones to chloroform solvent is proposed, in which both lone pairs on the N- and N-atoms can be involved in this process. The extent of the N- and N-atoms contributions in this electron-transfer process and also the retention or elimination of the C-substitutions are dependent on the nature and steric hindrance of both C- and N-substitutions.

Thermal electron-transfer-induced oxidation of 2-pyrazolines.

Various 3,5-diaryl-1-phenyl-2-pyrazolines were synthesized, and their thermal oxidation to their corresponding 2-pyrazoles was investigated using tetrabutylammonium peroxydisulfate in acetonitrile solution. Compared to the reported oxidative methods, this oxidizing agent provides a clean and non-expensive oxidative reaction in a short reaction time. Based on the proposed reaction mechanism, the extent of co-planarity of the C-aryl ring toward C=N double bond of the heterocyclic ring affects the electron-donating ability of the heterocyclic ring and decreases the time of oxidative reaction.

Computational and spectroscopic studies of a new Schiff base 3-hydroxy-4-methoxybenzylidene(2-hydroxyphenyl)amine and molecular structure of its corresponding zwitterionic form.

Computational and spectroscopic properties of a novel Schiff base compound, 3-hydroxy-4-methoxybenzylidene(2-hydroxyphenyl)amine were studied. The crystal structures of the title compound and its corresponding zwitterionic form were analyzed by X-ray diffraction. The presence of N-H, C-O and C=N stretching vibrations in IR spectrum strongly suggest that the title compound has zwitterionic form in the solid state.

Ultrasound-assisted dehydrogenation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones.

In this study, various 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones were synthesized and the dehydrogenation of these compounds by potassium peroxydisulfate in aqueous acetonitrile under thermal and sono-thermal conditions were investigated. Whereas the effect of the nature of 4-substituent influences the rate of reaction, the application of sonic waves decreases drastically the time of thermal reaction.

Sono-thermal oxidation of dihydropyrimidinones.

Combination of ultrasound and heat has been used for the oxidation of some ethyl 3,4-dihydropyrimidin-2(1H)-one-5-carboxylates to their corresponding ethyl pyrimidin-2(1H)-one-5-carboxylates by using potassium peroxydisulfate in aqueous acetonitrile. An ultrasonic probe of 24 kHz frequency has been used for this study. Whereas the use of ultrasound increases the rate of reactions compared with reactions at reflux conditions, the nature of 4-substituent on the dihydropyrimidinone ring affects also the rate of reaction.

Ultrasound-assisted photochemical oxidation of unsymmetrically substituted 1,4-dihydropyridines.

The combination of ultrasound and photochemistry has been used for the oxidation of unsymmetrical 1,4-dihydropyridines to the pyridine derivatives. An ultrasonic probe of 24 kHz frequency and a Hg-lamp of 100 W have been used for this study. The effect of parameters such as ultrasonic intensity, the presence of oxygen and argon atmospheres and also the separate usage of one of these irradiation sources have been studied.