Hydrogen bond

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

Crystal Structures and Properties of Nylon Polymers from Theory

Abstract: A complete force field (MSXX) for simulation of all nylon polymers is derived from ab initio quantum calculations. Special emphasis is given to the accuracy of the hydrogen bond potential for the amide unit and the torsional potential between the peptide and alkane fragments. The MSXX force field was used to predict the structures, moduli, and detailed geometries of all nine nylons for which there are experimental crystal data plus one other. For nylon-(2n) with 2n ≤ 6, the α crystal structure (with all-trans CH2 chains nearly coplanar with the hydrogen bonding plane) is more stable, while for 2n > 6, γ (with the alkane plane twisted by 70°) is more stable. This change results from the increased importance of methylene packing interactions over H bonds for larger 2n. We find the highest Young's modulus for nylon-7.

A new noncovalent force: comparison of P···N interaction with hydrogen and halogen bonds.

Abstract: When PH3 is paired with NH3, the two molecules are oriented such that the P and N atoms face one another directly, without the intermediacy of a H atom Quantum calculations indicate that this attraction is due in part to the transfer of electron density from the lone pair of the N atom to the σ* antibond of a P–H covalent bond Unlike a H-bond, the pertinent hydrogen is oriented about 180° away from, instead of toward, the N, and the N lone pair overlaps with the lobe of the P–H σ* orbital that is closest to the P In contrast to halogen bonds, there is no requirement of a σ-hole of positive electrostatic potential on the P atom, nor is it necessary for the two interacting atoms to be of differing potential In fact, the two atoms can be identical, as the global minimum of the PH3 homodimer has the same structure, characterized by a P ⋅⋅⋅ P attraction Natural bond orbital analysis, energy decomposition, and visualization of total electron density shifts reveal other similarities and differences between the three sorts of molecular interaction

Fast and Slow Dynamics of Hydrogen Bonds in Liquid Water

Abstract: We study hydrogen-bond dynamics in liquid water at low temperatures using molecular dynamics simulations, and find results supporting the hypothesized continuity of dynamic functions between the liquid and glassy states of water. We find that average bond lifetime $(\ensuremath{\sim}1\mathrm{ps})$ has Arrhenius temperature dependence. We also calculate the bond correlation function decay time $(\ensuremath{\sim}1\mathrm{ns})$ and find power-law behavior consistent with the predictions of the mode-coupling theory, suggesting that the slow dynamics of hydrogen bonds can be explained in the same framework as standard transport quantities.

The potential role of hydrogen bonding in aprotic and protic ionic liquids.

Abstract: Cohesion energies determine the phase behavior of materials. The understanding of interaction energies is in particular interesting for ionic liquids. Here we show experimentally that, in accord with theoretical work, the intermolecular cation-anion interactions in ionic liquids can be detected by far FTIR spectroscopy. The measured vibrational bands of aprotic and protic ionic liquids in the low-frequency range can be referred to the interaction strength between cations and anions in various combinations. It can be shown by DFT B3LYP calculations that these interactions are described by characteristic ratios between Coulomb forces and hydrogen bonds. These ratios can be tuned towards increasing hydrogen bond contributions which is reflected in important macroscopic properties of ionic liquids such as enthalpies of vaporization and viscosities. This opens a new path for tuning the desired properties of this new class of material.