Hydrogen bond

About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.

Study of the solvent effect on the enthalpies of homolytic and heterolytic N–H bond cleavage in p-phenylenediamine and tetracyano-p-phenylenediamine

Abstract: In this article, we have studied p-phenylenediamine (PPD) and tetracyano-p-phenylenediamine (TCPPD) molecules in order to study the effect of CN groups and the solvent effect on the enthalpies of homolytic and heterolytic N–H bond cleavage. Geometries of the molecules and reaction enthalpies related to hydrogen atom transfer, single electron transfer–proton transfer (SET–PT) mechanism and sequential proton loss electron transfer (SPLET) mechanisms were studied using DFT/UB3LYP/6-31++G∗∗ method. Ab initio MP2/6-31++G∗∗ method was used as the reference for the geometry calculation of the two molecules in vacuum. Solvent contribution to the enthalpies was computed employing integral equation formalism IEF-PCM method. Obtained results show that solvent is able to cause significant change in the reaction enthalpies of the stepwise SET–PT and SPLET mechanisms of hydrogen splitting-off from NH2 group. This may result in the change in thermodynamically preferred mechanism. Solvents also attenuate the CN-substituent effect in the case of SET–PT and SPLET mechanisms.

Hydrogen bonding and the cryoprotective properties of glycerol/water mixtures.

Abstract: Molecular dynamics simulations and infrared spectroscopy were used to determine the hydrogen bond patterns of glycerol and its mixtures with water. The ability of glycerol/water mixtures to inhibit ice crystallization is linked to the concentration of glycerol and the hydrogen bonding patterns formed by these solutions. At low glycerol concentrations, sufficient amounts of bulk-like water exist, and at low temperature, these solutions demonstrate crystallization. As the glycerol concentration is increased, the bulk-like water pool is eventually depleted. Water in the first hydration shell becomes concentrated around the polar groups of glycerol, and the alkyl groups of glycerol self-associate. Glycerol−glycerol hydrogen bonds become the dominant interaction in the first hydration shell, and the percolation nature of the water network is disturbed. At glycerol concentrations beyond this point, glycerol/water mixtures remain glassy at low temperatures and the glycerol−water hydrogen bond favors a more linea...

Role of C-H.cntdot..cntdot..cntdot.O hydrogen bonds in the coordination of water molecules. Analysis of neutron diffraction data

Abstract: C-H...O hydrogen bonds with water acceptors are analyzed from 101 water molecules in 46 neutron crystal structures. The shortest observed hydrogen bond distances are H...O W ∼2.3A and C...O W ∼3.1 A. About 8% of the water molecules accept C-H...O W interactions with H...O W separations<2.5 A AND 39% WITH H...O W <2.8 A. CH donors may coordinate to water molecules in concert with OH and NH donors and with metal ions in many different combinations. The most frequent function of C-H...O W hydrogen bonds is to complete a tetrahedral coordination geometry around the water

Adsorption-Enhanced Hydrolysis of β-1,4-Glucan on Graphene-Based Amorphous Carbon Bearing SO3H, COOH, and OH Groups

Abstract: The reaction mechanism of the hydrolysis of cellulose by a carbon-based solid acid, amorphous carbon containing graphene sheets bearing SO(3)H, COOH, and phenolic OH groups, has been investigated in detail through the hydrolysis of water-soluble beta-1,4-glucan. Whereas a range of solid strong Bronsted acid catalysts (inorganic oxides with acidic OH groups, SO(3)H-bearing resins, and the carbon-based solid acid) can hydrolyze the beta-1,4-glycosidic bonds in cellobiose (the shortest water-soluble beta-1,4-glucan), the tested solid acids except for the carbon material, consisting of conventional solid acids, cannot function as effective catalysts for the hydrolysis of cellohexaose (a long-chain water-soluble beta-1,4-glucan). However, the carbon material exhibits remarkable catalytic performance for the hydrolysis of cellohexaose: the turnover frequency (TOF) of SO(3)H groups in the carbon material exceeds ca. 20 times those of the conventional solid acids, reaching that of sulfuric acid, which is the most active catalyst. Experimental results revealed that inorganic oxides with acidic OH groups are not acidic enough to decompose the hydrogen and beta-1,4-glycosidic bonds in cellohexaose molecules aggregated by strong hydrogen bonds as well as cellulose and that the SO(3)H groups of the resins that do not adsorb beta-1,4-glucan are unable to attack the hydrogen and beta-1,4-glycosidic bonds in cellohexaose molecules effectively. In contrast, the carbon material is capable of adsorbing beta-1,4-glucan by phenolic OH or COOH groups in the carbon material, and SO(3)H groups bonded to the carbon therefore function as effective active sites for both decomposing the hydrogen bonds and hydrolyzing the beta-1,4-glycosidic bonds in the adsorbed long-chain water-soluble beta-1,4-glucan aggregate. These results suggest that the synergetic combination of high densities of the functional groups bonded to amorphous carbon causes the efficient hydrolysis of beta-1,4-glucan, including cellulose, on the carbon material.

Hydrogen bonding in organic synthesis

Abstract: Preface INTRODUCTION Introduction Hydrogen Bonding in Organic Synthesis HYDROGEN-BOND CATALYSIS OR BRONSTED-ACID CATALYSIS? GENERAL CONSIDERATIONS Introduction What is the Hydrogen Bond? Hydrogen-Bond Catalysis or Bronsted-Acid Catalysis Bronsted-Acid Catalysis Hydrogen-Bond Catalysis COMPUTATIONAL STUDIES OF ORGANOCATALYTIC PROCESSED BASED ON HYDROGEN BONDING Introduction Dynamic Kinetic Resolution (DKR) of Azlactones-Thioureas Can Act as Oxyanion Holes Comparable to Serine Hydrolases On the Bifunctionality of Chiral Thiourea-Tert-Amine-Based Organocatalysts: Competing Routes to C-C Bond Formation in a Michael Addition Dramatic Acceleration of Olefin Epoxidation in Fluorinated Alcohols: Activation of Hydrogen Peroxide by Multiple Hydrogen Bond Networks TADDOL-Promoted Enantioselective Hetero-Diels-Alder Reaction of Danishefsky's Diene with Benzaldehyde - Another Example for Catalysis by Cooperative Hydrogen Bonding Epilog OXYANION HOLES AND THEIR MIMICS Introduction What are Oxyanion Holes? A More Detailed Description of the Two Classes of Oxyanion Holes in Enzymes Oxyanion Hole Mimics Concluding Remarks BRONSTED ACIDS, H-BOND DONORS, AND COMBINED ACID SYSTEMS IN ASYMMETRIC CATALYSIS Introduction Bronsted Acid (Phosphoric Acid and Derivatives) N-H Hydrogen Bond Catalysts Combined Acid Catalysis (THIO)UREA ORGANOCATALYSTS Introduction and Background Synthetic Applications of Hydrogen-Bonding (Thio)urea Organocatalysts Summary and Outlook HIGHLIGHTS OF HYDROGEN BONDING IN TOTAL SYNTHESIS Introduction Intramolecular Hydrogen Bonding in Total Syntheses Intermolecular Hydrogen Bondings in Total Syntheses Conclusions