Tautomeric mixtures of 4-aryl substituted 5-acetyl-2-methoxydihydropyrimidines undergo oxidation by exposing to the UV-light under formation of sole pyrimidines. The nature of the 4-substitution and solvent, and the ratio of tautomeric mixtures affect the rate of reaction. A proposed electron transfer-induced photo-dehydrogenation supports the obtained results in this study.

Organic pi-conjugated compounds have attracted the interest of many researchers world wide due to their stability, high conductivity and intriguing optoelectrical properties. In this study, theoretical calculations were carried out to investigate the EFFECT of electron-withdrawing and electron-donating groups at a different position on electronic properties, geometry and photophysical parameters of bithiophene and bipyridine ring linked by a single bond using density functional theory (DFT) and time dependent DFT (TD-DFT). The calculated energy gap (Eg) of the studied co-oligomers with SUBSTITUENTs decreased with SUBSTITUENT strength. The reduction in the value of ɳ (1.54eV to 1.8eV) of the substituted co-oligomers compared with 1.95eV of unsubstituted co-oligomer implies lower resistance to distortion which enhances electron-withdrawing. The theoretical maximum absorption (λ-max) values for substituted compounds range between 335.4nm to 404.2nm compared with 318.2nm of an unsubstituted compound. Hence, the study results show that the substitute groups' nature, species, and position affect both the electronic and absorption properties without any significant difference in the geometry of the bithiophene-bipyridine co-oligomer. The mutual comparison of substituted and unsubstituted compounds shows a decrease in energy gap (Eg) and significantly reflected bathochromic shift for all substituted compounds, especially compound with NO2 SUBSTITUENT, indicating that the HOMO and LUMO level of the studied compounds were well controlled by the attached SUBSTITUENTs groups. Hence, it is expected to be useful for opto electronic material design.

The SUBSTITUENTs on cyclopentadienyl (Cp) can regulate the electronic EFFECT and hindrance of the active center in the metallocene catalyst. This modification can greatly change the catalytic activity of the catalyst and affect some features of the polymer. In order to study the EFFECT of alkyl SUBSTITUENTs on Cp in the performance of a typical metallocene catalyst Cp2TiCl2 for ethylene polymerization, two types of catalyst active centers were designed, including non-bridge [Cp2(R)TiCH3]+ and bridge [NCP2 (R)TiCH3]+ (R = H, Me, iPr). The EFFECTs of alkyl SUBSTITUENT steric hindrance were explored by density functional theory on the complex of catalyst active center with ethylene and the formation of transition state. The results showed that the increase of SUBSTITUENT steric hindrance was unfavorable to complex between ethylene monomer with catalyst active center. Moreover, the bigger alkyl SUBSTITUENT, the greater the activation energy of ethylene insertion into catalyst active center and the more difficult is ethylene polymerization. Therefore, the performance of metallocene catalysts could be regulated by the SUBSTITUENT on Cp.

In present computational survey, we are compared and contrasted electronic EFFECTs of C20 and its C20-2nTinBn heterofullerenic derivatives with n = 1-5, at density functional theory (DFT). All nanocages are true minima and none of them collapses to deformed open cage as segregated nanostructure. Isolating five single hetero bonds of Ti—B via either one double bond of C═C or one carbon atom is a suitable method for reaching highly substituted stable heterofullerene i.e. pen-shell C10Ti5B5 since it prevents from weak homo bonding of Ti—Ti and B—B. The C1-C18Ti1B1 heterofullerene can avoid from the most strained directly fused five-pentagon configuration, but its open-shell electronic structure with highly pyramidalized titanium atom (126.59° i.e. 3-4 times relation to C20) may render it too reactive to be observed under typical experimental conditions. The calculated binding energy (B.E.) shows C10Ti5B5 as the most stable heterofullerene. Contrary on B.E., the absolute heat of atomization of heterofullerenes decreases as number of substituting Ti―B unit (n) increases. Hence, substitution EFFECT on binding energy is more significant than heat of atomization. Compared to the previously reported material such Ti-decorated B38 nanofullerene as a suitable hydrogen storage with B.E. of 5.67 eV/atom, our studied C20-2nTinBn heterofullerenes show the higher B.E. with range of 12.25 to 38.03 eV/atom, the higher stability and the higher capacity for hydrogen storage. Interestingly, C18Ti1B1 heterofullerene must be not only kinetically stable against electronic excitations but also based on natural bond orbital (NBO) analysis, the highest charge transfer (CT) is take placed from πC=C bonds to the neighboring LP*B, LP*Ti and σ*Ti-B anti-bonds of it. Also, the exceptionally large value of nucleus-independent chemical shifts (NICS) is found for C18Ti1B1 compared to the archetypically aromatic benzene and [2.2]paracyclophane molecules.

Various ethyl 3,4-dihydropyrimidin-2(1H)-one-5-carboxylates were oxidized to their corresponding ethyl pyrimidin-2(1H)-one-5-carboxylates by potassium peroxydisulfate in refluxing aqueous acetonitrile. The products were obtained in good to excellent yields. The EFFECT of the nature of 4-SUBSTITUENT and also the nature of solvent play an important role on the rate of oxidation.

The concept of Resonance Assisted Hydrogen Bond (RAHB), which usually occurs in b diketons, has a remarkable role in chemistry. These molecules, which contain heteroatom particularly O and N, are species with biological interest in protein folding and DNA pairing.Therefore, the amplification of hydrogen bonds strength by SUBSTITUENTs may be important in life sciences. In the current research, we have shown that the nature of hydrogen bond in the enol form of heteroatom RAHB systems has partial covalent and electrostatic character. Nonetheless, the strength of hydrogen bonds increases by means of three different groups of SUBSTITUENTs, which cannot be attributed to the contributions of resonance structures. Parameters such as bond ellipticity, p delocalization indices and bond equalizations cannot help to prove the EFFECT of p-conjugation on the strength of hydrogen bond in RAHB systems. It is shown by NBO that the primary and secondary hyperconjugative charge transfer caused by SUBSTITUENTs help to amplify this type of hydrogen bond. We showed that the existence of p-conjugation is necessary only for transformation of electron from SUBSTITUENTs to the hydrogen bond as an acceptor of electrons.The strength of RAHB has a rather good correlation with the distance between of two nonconnected heteroatoms O and N according to reference [62].