Topic
Steric effects
About: Steric effects is a research topic. Over the lifetime, 16112 publications have been published within this topic receiving 319615 citations. The topic is also known as: steric hindrance.
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TL;DR: Different dihydroisoindol-4-ols and 8-hydroxytetrahydroisoquinolines were prepared by the gold-catalyzed phenol synthesis and the influence of the reaction time and the catalyst on the yield was investigated.
Abstract: Different dihydroisoindol-4-ols and 8-hydroxytetrahydroisoquinolines were prepared by the gold-catalyzed phenol synthesis The reaction was investigated with several sterically demanding groups in the 5-position of the furan starting material The influence of the reaction time and the catalyst on the yield was investigated
91 citations
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TL;DR: In this article, 13C NMR spectra were obtained for polymers made by ring-opening polymerization of cyclopentene and bicyclo[2.2]hept-2-ene respectively.
Abstract: 13C NMR spectra were obtained for polymers made by ring-opening polymerization of cyclopentene and bicyclo[2.2.1]hept-2-ene respectively. The fraction of cis double bonds could be determined with much greater precision from 13C NMR spectra than from IR spectra and varied from 0,66 to 0,31 for the samples of poly(1-pentenylene), (2), and from 1,0 to 0,14 for the samples of poly(1,3-cyclopentylenevinylene), (4). This is the first time an all-cis polymer of 4 has been reported.
The spectra of 2 showed a cis (upfield) and trans (downfield) peak for each of CH and α-CH2, but only one peak for β-CH2. The spectra of 4 showed multiple fine structure, the main splittings corresponding to a cis (upfield) and trans (downfield) peak for α-CH, and a reverse line order for the other three carbons; subsidiary splittings were observed for all but the olefinic carbons, interpreted in terms of sensitivity of the chemical shifts to the cis/trans structure at the next nearest double bond. A complete interpretation of the line orders in 4 is given in terms of steric compression effects. The possibility that ring tacticity accounts for some of the fine structure cannot be entirely discounted.
The stereochemistry of 4 is discussed in relation to the four possible modes of addition of monomer to a carbene chain carrier during polymerization.
91 citations
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TL;DR: The diastereofacial selectivity in reactions of a series of alkyl-substituted cyclohexyl radicals has been investigated in this article, and it has been found that only substituents bound at the olefinic center being attacked by the radical influence the equatorial-axial selectivity.
Abstract: The diastereofacial selectivity in reactions of a series of alkyl-substituted cyclohexyl radicals has been investigated. In additions of cyclohexyl radicals to alkenes, it has been found that only substituents bound at the olefinic center being attacked by the radical influence the equatorial-axial selectivity. Substituents bound to the radical center or axial substituents p to the radical center lead to increased axial attack. Equatorial /3-substituents or axial ?-substituents increase the amount of equatorial attack. The same trends are observed for halogen and hydrogen abstraction reactions; the amount of axial reaction product is usually somewhat higher than in the addition reactions. The stereoselectivities can be explained with steric and torsional effects very similar to those suggested for nucleophilic addition reactions to cyclohexanones. A MM2 force field has been parameterized to gain further insight into the stereochemistry of the reaction.
91 citations
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TL;DR: In this article, the effect of methoxy functionalization of three N-heterocyclic carbene ligands was assessed using a variety of methods, and the steric environment of each carbene has been assessed in various coordination environments.
91 citations