排序方式: 共有17条查询结果,搜索用时 9 毫秒
1.
Principal component analysis (PCA) is applied to 32 disubstituted unsaturated compounds (Y–CH2–X): cyanides, oximes and propenes; bearing 12 -substituents: F, Cl, Br, I, OMe, OEt, SMe, SEt, NMe2, NEt2, Me, and Et. The experimental 13C chemical shifts for the -carbon and functional carbon atoms are correlated with theoretically derived molecular properties, i.e. partial charges, electronegativity, hardness, dipole moments and the nuclear repulsion energies. In the first PCA, the clustering of these three classes of organic compounds occurred mostly because of the chemical shifts and partial charges, and also of the dipole moments, hardness and electronegativity parameters as confirmed by loading graph. A strong grouping is observed in the second PCA, showing the chemical shift dependence on the type of heteroatom substituents. Therefore, sulfur, nitrogen, oxygen and neutral groups exhibit four types of C-13 SCS influences, indicating that the heteroatom (Y) properties play a significant role on the effects on chemical shifts. The -halogenated compounds represent a very heterogeneous group due to possible orbital interactions between the functional group and the substituent. The third PCA shows the grouping of F, Cl, Br and I derivatives, confirming the second PCA results that same halogen presents the same or very similar effects on the chemical shifts. 相似文献
2.
B. Pihlar J. Marsel D. Tasic M. Erjavec 《Journal of Radioanalytical and Nuclear Chemistry》1978,44(2):333-344
Some parameters influencing the efficiency of labelling of bleomycin with99mTc using tin electrodes for electrolytic production of tin(II) ions were investigated. Different analytical techniques for
quality control of99mTc-bleomycin were applied. From the results obtained, it has been concluded that gel filtration on Sephadex G-25 can give
applicable information about the quality of this radiopharmaceutical. 相似文献
3.
Milena Simic Predrag Jovanovic Milos Petkovic Gordana Tasic Milos Jovanovic Vladimir Savic 《Journal of heterocyclic chemistry》2021,58(8):1665-1674
Octahydro-dipyrroloquinoline skeleton is the building component of a very few naturally occurring compounds. Nevertheless, these natural products have been attractive synthetic targets, and their study commanded development of efficient synthesis of this core. While the reported methods are based on the dimerization procedure of N-arylpyrrolidines of N-arylhomopropargyl amines, our approach relay on dipolar cycloaddition/amination sequence. This strategic approach allows sequential introduction of aromatic moieties increasing the product diversity and hence may be useful in further exploration of incargranine B or seneciobipyrrolidine derivatives. 相似文献
4.
Let , , , , be the usual operators on classes of rings: and for isomorphic and homomorphic images of rings and , , respectively for subrings, direct, and subdirect products of rings. If is a class of commutative rings with identity (and in general of any kind of algebraic structures), then the class is known to be the variety generated by the class . Although the class is in general a proper subclass of the class for many familiar varieties . Our goal is to give an example of a class of commutative rings with identity such that . As a consequence we will describe the structure of two partially ordered monoids of operators.
5.
Dimitrije Djukanovic Milos Petkovic Milena Simic Predrag Jovanovic Gordana Tasic Vladimir Savic 《Tetrahedron letters》2018,59(10):914-917
A one-pot, domino process was developed as an alternative approach for the preparation of 2-unsubstituted imidazolones. The methodology utilizes readily accessible bisamides, which upon a dehydration/cyclisation sequence produced imidazolones in good yields. The transformation relies on the compatibility of the dehydrating agent and base, and the reaction conditions tolerate various functional groups. 相似文献
6.
Gvozden S. Tasic Scepan S. Miljanic Milica P. Marceta Kaninski Djordje P. Saponjic Vladimir M. Nikolic 《Electrochemistry communications》2009,11(11):2097-2100
We have investigated the possibility of developing high-performance, cost-effective and durable non-noble Co metal electrocatalyst for PEMFC. In this work we applied electrodeposition process for PEMFC electrode preparation that is very efficient and far simpler than any other investigated method. The fuel cell with electrodeposited Co as anode catalyst has shown satisfying performance level. In determining FC’s operating conditions, subsequent electrochemical impedance and output power measurements were done, which enable the insight into the Co catalyst based anode behavior. Structure analysis of the electrodeposited anode layer was done by means of SEM and EDS technique. Although the Pt catalyst has higher efficiency, its cost performance ratio is significantly lower than for the Co catalyst, thus this investigation gives interesting possibilities in area of stationary fuel cell application. 相似文献
7.
8.
We investigate the variety of groups determined by the identity
and show that relatively free groupsin this variety are torsion free. This is done by proving theanalogous statement for Lie rings. The proof yields an affirmativeanswer to a question of Djokovi. 相似文献
9.
This work presents the substituent effects on the 1H and 13C NMR chemical shifts in the cis-isomer of 3-Y-cyclohexanols (Y = Cl, Br, I, CH3, N(CH3)2 and OCH3) and 3-Y-1-methoxycyclohexanes (Y = F, Cl, Br, I, CH3, N(CH3)2 and OCH3). It was observed that the H-3 chemical shift, due to the substituent alpha-effect, increases with the increase of substituent electronegativity when Y is from the second row of the periodic table of elements, (CH3 *sigma(C3--H3a) interaction energy. This interaction energy, for the halogenated compounds, decreases with an increase in size of the halogen, and this is a possible reason for the largest measured chemical shift for H-3 of the iodo-derivatives. The beta-effect of the analyzed compounds showed that the chemical shift of hydrogens at C-2 and C-4 increases with the decrease of n(Y) --> *sigma(C2-C3) and n(Y) --> *sigma(C3-C4) interaction energies, respectively, showing a behavior similar to H-3. The alpha-effect on 13C chemical shifts correlates well with substituent electronegativity, while the beta-effect is inversely related to electronegativity in halogenated compounds. NBO analysis indicated that the substituent inductive effect is the predominant effect on 13C NMR chemical shift changes for the alpha-carbon. It was also observed that C-2 and C-4 chemical shifts for compounds with N(CH3)2, OCH3 and F are more shielded in comparison to the compounds having a halogen, most probably because of the larger interaction of the lone pair of more electronegative atoms (n(N) > n(O) > n(F)) with *sigma(C2-C3), *sigma(C3-C4) and *sigma(C3-H3a) in comparison with the same type of interaction with the lone pair of the other halogens. 相似文献
10.
Sanja Vujovi Jana Desnica Dragana Stanii Irena Ognjanovi Momir Stevanovic Gvozden Rosic 《Molecules (Basel, Switzerland)》2022,27(17)
Reconstruction of defects in the maxillofacial region following traumatic injuries, craniofacial deformities, defects from tumor removal, or infections in the maxillofacial area represents a major challenge for surgeons. Various materials have been studied for the reconstruction of defects in the maxillofacial area. Biodegradable metals have been widely researched due to their excellent biological properties. Magnesium (Mg) and Mg-based materials have been extensively studied for tissue regeneration procedures due to biodegradability, mechanical characteristics, osteogenic capacity, biocompatibility, and antibacterial properties. The aim of this review was to analyze and discuss the applications of Mg and Mg-based materials in reconstructive oral and maxillofacial surgery in the fields of guided bone regeneration, dental implantology, fixation of facial bone fractures and soft tissue regeneration. 相似文献