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Substituent

About: Substituent is a research topic. Over the lifetime, 42877 publications have been published within this topic receiving 516716 citations. The topic is also known as: side chain & side group.


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Journal ArticleDOI
TL;DR: In this paper, an unstable associate of the 6-cis and 2,6-dicis-2-4 retinals and bacterioopsin is formed, possibly allowed by the lack of the cyclohexyl ring and thus the greater flexibility of the chromophore.
Abstract: samples at 80 K. The C-C band at 1558 cm-' represents the initial all-trans pigment while that at 1575 cm-* almost certainly arises from the short-wavelength M-type intermediate absorbing at ca. 380 nm. The results agree with previously determined correlation between A, and C=C stretching frequency and expected temperature dependence of M formation.12 On combination of the 6-cis and 2,6-dicis isomers of 2-4 with bacterioopsin, a broad absorption is noted with a A, , of 450-460 nm with a shoulder at 510 nm. Extraction of the pigment with methylene chloride yields the respective 6-cis or 2,6-dicis isomer. These pigments are rapidly (5 min) destroyed by hydroxylamine or all-trans-retinal. On irradiation, the absorption shifts to 487 nm, increases in intensity, and is identical with that of the all-trans pigments. Only the respective all-trans isomer is obtained when these irradiated pigments are extracted with methylene chloride. These results indicate that an unstable associate of the 6-cisand 2,6-dicis-2-4 retinals and bacterioopsin is formed, possibly allowed by the lack of the cyclohexyl ring and thus the greater flexibility of the chromophore. The above experiments demonstrate that these acyclic chromophores can form pigments with bacterioopsin which show light-induced absorption and pH changes. As these retinal derivatives lack both a cyclohexyl ring and the fifth C=C, neither of these structural elements are evidently essential for these functions of the pigment. A similar but more restrictive conclusion has been proposed for the 5,6-ethylene bond by our studies of the 5,6-dihydroretinal pigments.13 These results are consistent with isomerization and charge separation being thd primary event14 and indicate that the proton pumping and photocycling are dependent on the polyene chain portion of the retinal chromophore.

89 citations

Journal ArticleDOI
TL;DR: In this paper, a micellar arrangement of compact SSQO domains with a correlation distance corresponding to the size of the substituent is formed, and the ordering is promoted by increasing length of the organic chain.
Abstract: Sol−gel polymerization of organotrialkoxysilanes RSi(OR‘)3 and formation of silsesquioxane (SSQO) structures was followed using SEC, 29Si NMR, and both small- and wide-angle X-ray scattering. Evolution of the SSQO structure is controlled by the competition between intermolecular polycondensation and cyclization. A strong tendency to buildup of polyhedral cyclic oligomersmainly octamer “cages” and larger cagelike structureswas found to grow with increasing size of substituent R. As a result, long substituents prevent gelation of the trifunctional system and increase stability of the SSQO. Because of incompatibility of the polyhedral SSQO framework and pendant organic chains, microphase separation takes place and spontaneous self-organization occurs. A micellar arrangement of compact SSQO domains with a correlation distance corresponding to the size of the substituent is formed, and the ordering is promoted by increasing length of the organic chain. The most organized arrangement was observed with the trial...

89 citations

Journal ArticleDOI
TL;DR: In this article, the nonpolar character of a series of tetraalkylammonium dialkyldithiocarbamate ion pairs was influenced by the chain length of the alkyl substituent on the carbamate nitrogen and to a lesser extent, by the ammonium counterion.
Abstract: Measurements of solubilities in supercritical CO 2 corroborated the hypothesis that the nonpolar character of a series of tetraalkylammonium dialkyldithiocarbamate ion pairs was influenced (i) primarly by the chain length of the alkyl substituent on the carbamate nitrogen and (ii) to a lesser extent, by the chain length of the alkyl substituent(s) on the ammonium counterion. Similarly, the solubility of Zn-dithiocarbamate complexes decreased in the order dibutyl (DBDTC)>diethyl >pyrrolidine. An extraction protocol in which SC-CO 2 was saturated with tetrabutylammonium DBDTC prior to dynamic complexation/mobilization of 12-20 μg/mL Zn, Cd, or Pb analyte from aqueous solution resulted in >73% and >94% analyte removal within 5 and 15 min extraction, respectively

89 citations

Journal ArticleDOI
TL;DR: In this article, Hartree−Fock calculations with a 6-31G* basis set were performed on 2,6-dimethylphenol (DMP or monomer) and 4-(2, 6-dimmethylphenoxy)-2,6dimethyl phenol (dimer) to gain more insight into the mechanism of the copper-catalyzed oxidative phenol coupling reaction.
Abstract: Ab initio unrestricted Hartree−Fock calculations with a 6-31G* basis set were performed on 2,6-dimethylphenol (DMP or monomer) and 4-(2,6-dimethylphenoxy)-2,6-dimethylphenol (dimer) to gain more insight into the mechanism of the copper-catalyzed oxidative phenol coupling reaction. Atomic charges were determined for the phenol, phenoxyl radical, phenolate anion and phenoxonium cation (both the singlet and triplet state) of both species. Calculations for the monomer show that the only aromatic carbon atom bearing a partial positive atomic charge is the para carbon of the cation in the singlet state. In the case of the dimer, the presence of a p-phenoxy substituent results in a partial positive charge for the para carbon of the first aromatic ring in all states, but this charge is significantly higher for the singlet cation. In the singlet cationic state, the para carbon of the first aromatic ring is therefore the site most susceptible to nucleophilic aromatic substitution. This result strongly supports a pr...

89 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023660
20221,273
2021568
2020787
2019753
2018858