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Hydrogen bond introduced

The second reason is that every -OH—O hydrogen bond involves knowledge of the -C-O-H torsion angle. This means that each hydrogen bond introduced into the molecular model involves at least one additional variable parameter and preferably more. The assumptions that hydrogen bonds are linear and that the hydrogen atom... [Pg.22]

By this technique an average value is measured. From this the authors calculated a mean amplitude 02 = 18.3° in H20 HF which is lower than the corresponding values for rare gas atom HF complexes Ar HF, 02 = 41.1° and Kr HF, 02 = 39.2°49,50). As expected, hydrogen bonding introduces some rigidity into the complex However, the isotope effect on 02 in H20 HF is not yet clear48 . [Pg.19]

To the extent that the local bonding of a-Si H is similar to that of crystalline silicon, the phonon spectrum is also little different. Some broadening of the phonon density of states is expected because of the disorder in bond strength. The hydrogen bonding introduces additional... [Pg.40]

Hydrogen bonding (introduced in Section 3.4) is relevant to most scientific disciplines. The definition of a hydrogen bond in terms of its covalent and ionic contributions continues to be debated. Its traditional definition, a force that arises between molecules that have an H atom bonded to a small, highly electronegative atom with lone pairs, usually N, O, or F, has been considerably broadened. The lUPAC Physical and Biophysical Chanistry Division has recommended a new definition that includes the following themes. [Pg.197]

By using an effective, distance-dependent dielectric constant, the ability of bulk water to reduce electrostatic interactions can be mimicked without the presence of explicit solvent molecules. One disadvantage of aU vacuum simulations, corrected for shielding effects or not, is the fact that they cannot account for the ability of water molecules to form hydrogen bonds with charged and polar surface residues of a protein. As a result, adjacent polar side chains interact with each other and not with the solvent, thus introducing additional errors. [Pg.364]

The representation of molecules by molecular surface properties was introduced in Section 2.10. Different properties such as the electrostatic potential, hydrogen bonding potential, or hydrophobicity potential can be mapped to this surface and seiwe for shape analysis [44] or the calculation of surface autocorrelation vectors (refer to Section 8.4.2). [Pg.427]

Secondary Bonding. The atoms in a polymer molecule are held together by primary covalent bonds. Linear and branched chains are held together by secondary bonds hydrogen bonds, dipole interactions, and dispersion or van der Waal s forces. By copolymerization with minor amounts of acryhc (CH2=CHCOOH) or methacrylic acid followed by neutralization, ionic bonding can also be introduced between chains. Such polymers are known as ionomers (qv). [Pg.431]

In substitutive nomenclature the use of the prefix oxo- or the suffix -one means the insertion of =0 in place of two hydrogen atoms. This is straightforward when the parent carries a CHz group at the appropriate position (example 206), but often the insertion of =0 requires prior reduction of a double bond. When the prefix oxo- is employed, this is achieved by using the appropriate hydro- prefix terms (example 207). However, the suffix -one can be used without hydro , the required reduction being implied rather than overtly stated (example 208) if desired the position of the hydrogen atom introduced to accommodate the carbonyl can be indicated in parentheses (see also examples 123 and 124). [Pg.44]

Proline is the only amino acid in Table 27.1 that is a secondary amine, and its presence in a peptide chain introduces an amide nitrogen that has no hydrogen available for hydrogen bonding. This disrupts the network of hydrogen bonds and divides the peptide into two separate regions of a helix. The presence of proline is often associated with a bend in the peptide chain. [Pg.1144]

More complicated and less known than the structure of pure water is the structure of aqueous solutions. In all cases, the structure of water is changed, more or less, by dissolved substances. A quantitative measure for the influence of solutes on the structure of water was given in 1933 by Bernal and Fowler 23), introducing the terminus structure temperature, Tsl . This is the temperature at which any property of pure water has the same value as the solution at 20 °C. If a solute increases Tst, the number of hydrogen bonded water molecules is decreased and therefore it is called a water structure breaker . Vice versa, a Tsl decreasing solute is called a water structure maker . Concomitantly the mobility of water molecules becomes higher or lower, respectively. [Pg.4]

One hypothesis proposes a destabilizing, repulsive interaction between two occupied orbitals. The equatorial transition state is destabilized compared to the axial transition state by torsional strain which is introduced by bond eclipsing of the incipient bond with the axial C-2 and C-6 carbon-hydrogen bonds. This Felkin model33 37 relies on the assumption that an incipient bond, even if it is only partially formed, suffers from severe repulsion in the case of eclipsing vicinal tr-bonds. [Pg.7]

Other considerations aside, the use of dilute reagents minimizes effects of nonideality. This allows the use of concentrations in place of activities. Of course, the time scale, the sensitivity of the analytical method at different concentrations, and the use of other reaction components introduce additional considerations. Tied closely to this decision is the choice of solvent. Reaction rates may (or may not) be affected by such variables as polarity, dielectric constant, hydrogen-bonding ability, donor capacity, and viscosity. A change in solvent may change not only the rate but also the mechanism and possibly even the products. One cannot even assume that the net reaction is the... [Pg.10]

Recently, Kamlet and Taft introduced new elaborate parameters in order to explain the linear energy relationship for the formation of the hydrogen bond between HBA (hydrogen bond acceptor) and HBD (hydrogen bond donor). They treated several sulphoxides as HBA. The detailed presentations and actual treatments of these parameters have been described in their recent review article72. [Pg.552]


See other pages where Hydrogen bond introduced is mentioned: [Pg.45]    [Pg.505]    [Pg.563]    [Pg.366]    [Pg.529]    [Pg.63]    [Pg.45]    [Pg.505]    [Pg.563]    [Pg.366]    [Pg.529]    [Pg.63]    [Pg.136]    [Pg.351]    [Pg.383]    [Pg.22]    [Pg.1144]    [Pg.150]    [Pg.63]    [Pg.126]    [Pg.361]    [Pg.470]    [Pg.255]    [Pg.255]    [Pg.535]    [Pg.98]    [Pg.288]    [Pg.447]    [Pg.140]    [Pg.170]    [Pg.277]    [Pg.44]    [Pg.1144]    [Pg.241]    [Pg.176]    [Pg.172]    [Pg.44]    [Pg.173]    [Pg.154]    [Pg.390]    [Pg.461]    [Pg.175]    [Pg.287]    [Pg.520]   
See also in sourсe #XX -- [ Pg.197 ]




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