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121.
A reverse ortho effect is observed for the (13)C NMR chemical shifts of the carboxyl carbon (δ(co)) in benzoic acids measured in aprotic solvents of varying polarity. The ortho effect on δ(co) is best described by a combination of the reverse field and steric accelerating effects of the substituent in an 80: 20 pattern in apolar aprotic solvents and a 60: 40 pattern in dipolar aprotic ones. Interestingly, no good enough correlation was found between δ(co) and log k(1) of the acids measured in similar solvents. A critical analysis of the results clearly indicates the use of an apolar aprotic solvent and not a dipolar aprotic one as the solvent of choice for investigating intrinsic substituent effects on δ(c) in an aromatic system. 相似文献
122.
A Novel Synthetic Protocol for the Heteroannulation of Oxocarbazole and Oxoazacarbazole Derivatives through Corresponding Oxoketene Dithioacetals 下载免费PDF全文
Ruchi Tyagi Navjeet Kaur Bhawani Singh Dharma Kishore 《Journal of heterocyclic chemistry》2014,51(1):18-23
An efficient novel strategy for the heteroannulation of 6,7‐dihydropyrazolo[3,4‐b]carbazol‐8(1H,5H,9H)‐one 4 and 5‐N‐benzyl‐6,7‐dihydropyrazolo[3,4‐b]carbazol‐8(1H,9H)‐one 5 has been developed to allow the incorporation of pyrazole, isoxazole, pyrimidine, benzodiazepine, and benzothiazepine rings through their corresponding oxoketene dithioacetal derivatives 6 and 7 , respectively. 相似文献
123.
A new terphenyl-based macrocycle 5 incorporating phenanthroline as a fluorophore has been designed, synthesized and examined for its recognition ability toward various cations (Pb(2+), Hg(2+), Ba(2+), Cd(2+), Ag(+), Zn(2+), Cu(2+), Ni(2+), Co(2+), K(+), Mg(2+), Na(+) and Li(+)) by UV-vis, fluorescence and NMR spectroscopy. The receptor 5 showed highly selective 'Off-On' fluorescence signaling behavior for Zn(2+) ions in THF. Interestingly, the addition of H(2)PO(4)(-) ions to the [5-Zn] complex regulates the binding site for additional Zn(2+) ions and hence leads to a blue-shifted emission band. 相似文献
124.
We have designed and synthesized a HAB-based receptor with six ethereal oxygens on one face of the central benzene ring by a trimerization of a diarylacetylene in which the ethereal oxygens are tied together with a tetramethylene bridge. This unique amphiphilic receptor allows an efficient binding of a single potassium cation by a synergistic interaction with the polar ethereal fence and with the central benzene ring via cation-pi interaction. Furthermore, the ready accessibility of this unique receptor with a bipolar binding pocket will allow the exploration of its usage for developing efficient sensing devices for various metal cations. 相似文献
125.
The antibacterial activity of Aloe barbadensis was tested on clinically isolated bacterial pathogens i.e. Enterococcus bovis, Staphylococcus aureus, Escherichia coli, Proteus vulgaris, Proteus mirabilis, Pseudomonas aeruginosa,
Morganella morganii, and Klebsiella pneumoniae causing infection in human being. Ethanolic and aqueous extracts were used for the antibacterial effect, which was measured
by the appearance of zone of inhibition. Relatively higher MIC concentrations were obtained for gram negative bacteria E. coli and K. pneumoniae, with ethanol extract; however, no inhibitory effect was noted for aqueous extract. Ethanolic extract possesses great inhibitory
activity for gram positive bacteria, E. bovis followed by S. aureus. Among gram negative bacteria, highest inhibitory effect was observed with P. aeruginosa, followed by M. morganii, P. mirabilis, and P. vulgaris, which was significant (p < 0.01) than E. coli and K. pneumoniae. Antimicrobial activity tests of crude extract of A. barbadensis were carried out to validate the use of traditional medicinal herbal and results of this study tend to give credence to the
common use of A. barbadensis gel and leaf. 相似文献
126.
Anomalous (reverse) substituent-induced 13C nuclear magnetic resonance chemical shifts at the carboxyl carbon (δco) in meta-substituted benzoic acids have been studied for 11 substituents having varying electronic effects in 4 aprotic (nonhydroxylic)
solvents of varying polarity by employing different dual substituent parameter models. The regression results for apolar aprotic
solvents provide a strong evidence for through space π-polarization mode of transmission of reverse meta-substituent effects on the carboxyl carbon in benzoic acids. The results for dipolar aprotic solvents indicate significant
specific solvation of π-polarized forms of the acids. The study showed further that an apolar aprotic solvent has a distinct
preference over a dipolar aprotic one for investigating intrinsic substituent effects on chemical shifts in aromatic molecules. 相似文献