Hydrogen bonding normal

For reference, terminal boron-hydrogen bonds normally exhibit J 1 1b h in the range 100-190 Hz, whereas when a hydrogen bridge is involved JUb-h is usually less... 

Influence of Solvents. The stress-strain curves of untreated and ether-extracted corneum in water show marked differences (81). Untreated corneum, extended 5% and relaxed, shows hysteresis similar to that observed for other keratinaceous structures (Figure 35). The deformation mechanism is completely reversible, and hydrogen-bond breakdown and slow reformation may be the major factors determining the stress-strain relationships. With ether-extracted samples, complete recovery is observed from 5% extension but with little or no hysteresis. The more rapid swelling and lack of hysteresis of ether-extracted corneum in water may be related to the breakdown of hydrogen bonds normally shielded from the eflFects of water by the lipid-like materials removed by ether. 

Figure 5.1. Hydrogen bonding normal-phase mechanism in SPE using a cyanopropyl sorbent.

Liquid-crystalline materials of types A-I and A-II exhibit homogeneous (non-phase separated) mesophases by the association of identical or different molecules. A new class of mesomorphic H-bonded materials, anisotropic liquid-crystalline gels (Fig. 2, Type B), has recently been prepared by the selfaggregation of H-bonded molecules in non-hydrogen-bonded normal liquid crystals [29, 30]. These materials are macroscopically soft solids and form heterogeneous (phase-separated) structures consisting of liquid crystals and fibrous solids. 

The attractive force is called hydrogen bonding and is normally represented by a dotted line, for example A—H A—H it is this... 

The ideas of Frank, Evans and Kauzmann had a profound influence on the way chemists thought about hydrophobic effects in the decades that followed However, after the study of the hydrophobic hydration shell through computer simulations became feasible, the ideas about the hydrophobic hydration gradually changed. It became apparent that the hydrogen bonds in the hydrophobic hydration shell are nof or only to a minor extent, stronger than in normal water which is not compatible with an iceberg character of the hydration shell. 

Hydrogen bonding of water to the activating group of (for normal-electron demand Diels-Alder reactions) the dienophile constitutes the second important effect". Hydrogen bonds strengthen the electron-withdrawing capacity of this functionality and thereby decrease the HOMO-LUMO gap... 

Dou ble hel ix (Section 28 8) The form in which DNA normally occurs in living systems Two complementary strands of DNA are associated with each other by hydrogen bonds be tween their base pairs and each DNA strand adopts a helical shape... 

Nucleophilic addition (Section 17 6) The charactenstic reac tion of an aldehyde or a ketone An atom possessing an un shared electron pair bonds to the carbon of the C=0 group and some other species (normally hydrogen) bonds to the oxygen... 

Podates AcycHc analogues of crown ethers /coronands and cryptands (podands, eg, (11) (30) are also capable of forming inclusion compounds (podates) with cations and uncharged organic molecules, the latter being endowed with a hydrogen bond fiinctionahty. Podates normally are less stable than coronates and cryptates but have favorable kinetics. 

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