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: The first unsymmetrically substituted dialkylgermylene, Me 5 C 5 GeCH(SiMe 3 ) 2 with LiC-(SiME 3 ) 3, was shown to be stable at ambient temperature in this article.
86 citations
86 citations
TL;DR: The rate constants for alkoxyamines carrying the styryl (PhEt) group as leaving alkyl radical in terms of polar inductive/field (sigmaL) and steric (Es) effects of the nitroxide substituents are shown to increase with the increasing electron-donating capacities, the steric demand, and the intramolecular bonding capabilities of the substituent.
Abstract: Alkoxyamines and persistent nitroxyl radicals are important regulators of living radical polymerizations. Because polymerization times decrease with the increasing rate of the homolytic C−O bond cleavage between the polymer chain and the nitroxide moiety, the factors influencing the homolysis rate are of considerable interest. Here, we present an analysis of the cleavage rate constants for 28 alkoxyamines carrying the styryl (PhEt) group as leaving alkyl radical in terms of polar inductive/field (σL) and steric (Es) effects of the nitroxide substituents, using the Taft−Ingold equation, i.e., log(k/k0) = ρLσL + δEs. The rate constants are shown to increase with the increasing electron-donating capacities, the steric demand, and the intramolecular (hydrogen) bonding capabilities of the substituents. A good correlation, (R2 = 0.95, 23 data) log kd = −3.07σL − 0.88Es − 5.88, is obtained, which should facilitate the design of new nitroxyl radicals and alkoxyamine regulators.
86 citations
TL;DR: Using Fourier transform infrared spectroscopy, the authors in this article measured the extent of intra-and intermolecular hydrogen bonding in 2-methoxy-ethanol and 2-butoxyethanol at varying concentrations and temperatures.
Abstract: Glycol−ether compounds such as 2-methoxyethanol (CH3OCH2CH2OH) and 2-butoxyethanol [CH3(CH2)3OCH2CH2OH] form both intra- and intermolecular hydrogen bonds. Using Fourier transform infrared spectroscopy, we have measured extent of intra- and intermolecular hydrogen bonding in these compounds dissolved in n-hexane at varying concentrations and temperatures. Intramolecular hydrogen bonds are present at all conditions, whereas intermolecular bonds appear at higher concentrations. Using lattice-fluid-hydrogen-bonding theory, equilibrium constants for the formation of intra- and intermolecular hydrogen bonds are determined. The results show that the equilibrium constant for intermolecular bond formation is approximately 6 times the intramolecular equilibrium constant for 2-methoxyethanol systems at 35 °C. Experiments at higher temperature, 45 °C, with 2-methoxyethanol show less hydrogen bonding as expected due to higher thermal energy. Due to steric hindrance, 2-butoxyethanol has a lower degree of hydrogen bond...
86 citations
TL;DR: In this article, the product distribution from nucleophilic attack on (η3-allyl)palladium complexes is analyzed by a combination of molecular mechanics and QSAR techniques.
86 citations