Topic
Hydrogen bond
About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.
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TL;DR: It is hypothesized that the effects due to a loss in hydrogen bonding are outweighed by those due to the reduction in entropy, which leads to greater ordering within the liquid raising the melting point and increasing viscosity.
Abstract: 1-Butyl-3-methyl-imidazolium chloride ([C4C1im]Cl) is a prototypical ionic liquid. Substitution for a methyl group at the 2-position of the cation to form 1-butyl-2,3-dimethyl-imidazolium ([C4C1mim]+) eliminates the main hydrogen-bonding interaction between the Cl anion and the imidazolium cation. Loss of this hydrogen-bonding interaction could be expected to lead to a reduction in melting point and a decrease in viscosity; however the opposite is observed experimentally; melting points and viscosity increase. The gas-phase structure and electronic properties of ion pairs formed from [C4C1mim]+ and Cl- are investigated to offer insight into this counter-intuitive behavior. We hypothesize that the effects due to a loss in hydrogen bonding are outweighed by those due to a loss in entropy. The amount of disorder in the system is reduced in two ways: elimination of ion-pair conformers, which are stable for [C4C1im]Cl but not [C4C1mim]Cl, and an increase in the rotational barrier of the butyl chain, which lim...
342 citations
TL;DR: The lifetime of the hydrogen bond between a PHG and a water molecule is found to be much longer than that between any two water molecules, and is likely to be a general feature of hydrophilic surfaces of organized assemblies.
Abstract: The dynamics of hydrogen bonds among water molecules themselves and with the polar head groups (PHG) at a micellar surface have been investigated by long molecular dynamics simulations. The lifetime of the hydrogen bond between a PHG and a water molecule is found to be much longer than that between any two water molecules, and is likely to be a general feature of hydrophilic surfaces of organized assemblies. Analyses of individual water trajectories suggest that water molecules can remain bound to the micellar surface for more than 100 ps. The activation energy for such a transition from the bound to a free state for the water molecules is estimated to be about 3.5 kcal/mol.
339 citations
TL;DR: In this article, the synthesis of neutral macrocyclic anion receptors and their anion binding properties is discussed. But the synthesis is not restricted to macro-cyclic scaffolds.
338 citations
TL;DR: The studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for α C-H bonds in alcohols in the presence of allylic, benzylic, α-C=O, and α-ether C–H bonds.
Abstract: The efficiency and selectivity of hydrogen atom transfer from organic molecules are often difficult to control in the presence of multiple potential hydrogen atom donors and acceptors. Here, we describe the mechanistic evaluation of a mode of catalytic activation that accomplishes the highly selective photoredox α-alkylation/lactonization of alcohols with methyl acrylate via a hydrogen atom transfer mechanism. Our studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for α C–H bonds in alcohols in the presence of allylic, benzylic, α-C=O, and α-ether C–H bonds.
337 citations
TL;DR: A detailed experimental study of the water trimer shows a chiral six-membered ring structure with rapid quantum tunneling occurring between the enantiomers, speculated that larger water clusters would also exhibit transient chirality and that similar effects may be found in liquid water.
Abstract: A detailed experimental study of the water trimer is reported. A vibration-rotation-tunneling band of the perdeuterated cluster has been measured near 89.6 wave numbers by tunable far infrared laser absorption spectroscopy. The data indicate a chiral six-membered ring structure with rapid quantum tunneling occurring between the enantiomers. The observed vibration involves torsional motion of the water subunits about each hydrogen bond axis. It is speculated that larger water clusters would also exhibit transient chirality and that similar effects may be found in liquid water.
337 citations