Topic
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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83 citations
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TL;DR: This work extends the original investigations to many more substituents and provides a comprehensive theory of substituent effects on geometries and reaction rates.
Abstract: Substituent effects on the geometries and conrotatory electrocyclic ring openings of cyclobutenes were studied. This work extends the original investigations to many more substituents and provides a comprehensive theory of substituent effects on geometries and reaction rates. The effects of substitution at the 1 position are minimal; donor substituents raise the activation energy slightly, and powerful acceptor substituents slightly lower the activation energy. Substituents on C3 cause small distortions of the cyclobutene geometry, in the same direction as the favored stereochemistry of reaction. Donors prefer outward rotation, while strong acceptors prefer inward rotation. The activation energy changes and cyclobutene geometrical perturbations were found to correlate with Taft σR0 parameters. Amino, hydroxy, fluoro, chloro, methyl, cyano, formyl, and vinyl substituents were studied in the 1 position. Boryl, dimethylboryl, nitroso, formyl, nitro, carboxyl (neutral, protonated, and deprotonated), cyano, tr...
83 citations
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TL;DR: The reliability of the estimates is still affected by the uncertainties assigned to many of those experimental results and also by the scarce information on the solvation of phenoxy radicals as discussed by the authors, however, the reliability of these estimates is improved by using a group additivity method.
Abstract: The available experimental data on O-H bond dissociation enthalpies in phenolic compounds indicate that the ring substituent effects on the thermodynamic stability of that bond can be predicted by using a group additivity method. However, the reliability of the estimates is still affected by the uncertainties assigned to many of those experimental results and also by the scarce information on the solvation of phenoxy radicals.
82 citations
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TL;DR: Addition of the 3 alpha, 7 alpha, and 12 alpha hydroxyl substituent effects derived from the mono- and dihydroxycholanoic acids yielded predicted values for proton chemical shifts of the trihydroxy-substituted 5 beta-cholaneic acid, cholic acid that agreed well with experimental values.
82 citations
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TL;DR: Mechanistic studies elucidated the sequence of hydrosilylation in this multiple reduction cascade: 1,2- or 1,4-hydrosilylated as an initial step depending on the substituent position, followed by selective hydrosallylation of enamine double bonds eventually affording β-silylated azacyclic compounds.
Abstract: Tris(pentafluorophenyl)borane-catalyzed silylative reduction of pyridines has been developed giving rise to the formation of sp(3) C-Si bonds selectively beta to the nitrogen atom of azacyclic products. Depending on the position and nature of pyridine substituents, structurally diverse azacycles are obtained with high selectivity under the borane catalysis. Mechanistic studies elucidated the sequence of hydrosilylation in this multiple reduction cascade: 1,2- or 1,4-hydrosilylation as an initial step depending on the substituent position, followed by selective hydrosilylation of enamine double bonds eventually affording β-silylated azacyclic compounds.
82 citations