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Consequently, hydrogen bonds between or within solute molecules dissolved in water are almost always unfavorable relative to hydrogen bonds between water and the donors and acceptors for hydrogen bonds on those solutes. [44] Hydrogen bonds between water molecules have an average lifetime of 10 −11 seconds, or 10 picoseconds. [45]
These strong hydrogen bonds, for example, result in the high tensile strength and melting point of polymers containing urethane or urea linkages. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups.
For instance, supramolecular polymerization of a hydrogen bonding porphyrin-based monomer in a hydrocarbon solvent containing a minute amount of a hydrogen bond scavenging alcohol shows distinct pathways, i.e. polymerization favored both by cooling as well as heating, and is known as "thermally bisignate supramolecular polymerization".
A hydrogen bond is a specific dipole where a hydrogen atom has a partial positive charge (δ+) to due a neighboring electronegative atom or functional group. [9] [10] Hydrogen bonds are amongst the strong intermolecular interactions know other than ion-dipole interactions. [10]
Hydrogen bonds of the form A--H•••B occur when A and B are two highly electronegative atoms (usually N, O or F) such that A forms a highly polar covalent bond with H so that H has a partial positive charge, and B has a lone pair of electrons which is attracted to this partial positive charge and forms a hydrogen bond.
As this example shows, there can be no sharp boundary between molecular and network covalent solids. Intermediate kinds of bonding: A solid with extensive hydrogen bonding will be considered a molecular solid, yet strong hydrogen bonds can have a significant degree of covalent character. As noted above, covalent and ionic bonds form a continuum ...
For example, residue i may form hydrogen bonds to residues j − 1 and j + 1; this is known as a wide pair of hydrogen bonds. By contrast, residue j may hydrogen-bond to different residues altogether, or to none at all. The hydrogen bond arrangement in parallel beta sheet resembles that in an amide ring motif with 11 atoms.
Hydrogen bonds contribute to the stability of ion pairs with e.g. protonated ammonium ions, and with anions is formed by deprotonation as in the case of carboxylate, phosphate etc; then the association constants depend on the pH. Entropic driving forces for ion pairing (in absence of significant H-bonding contributions) are also found in ...