Hydrogen-bonded molecules

The dipole moment in Eq. (2-73) is in debyes, while P is in atm and is in K. Units must be watched carefully. For hydrogen-bonding molecules, Eq. (2-71) can be used with a value of Bo calculated by Eq. 

Chain extenders are usually low molecular weight symmetrical diols or diamines. Chain extenders react with isocyanates in the same way as polyols do, but because they are low molecular weight, a high concentration of hydrogen-bonded molecules can associate and phase out of the polyol to form plastic-like domains called hard segments . Hard segments will be discussed in Section 4. Some of the more common diol and diamine chain extenders are shown in Table 3. 

Because of the electric interaction, hydrogen-bonded molecules hold on to each other more tightly than those in substances with pure covalent bonds. This cohesiveness is why water is a liquid at room temperature, whereas heavier covalent-bonded molecules such as chlorine, in the form of CI2, are gases. 

Intermolecular forces may be caused by a solute molecule having a dipole moment, when it can interact selectively with other dipoles. If a molecule is a good proton donor or acceptor it can interact with other such molecules by hydrogen bonding. Molecules can also interact via much weaker dispersion forces which rely on a given molecule being polarised by another molecule. 

On file other hand, this reaction is endothermic by almost 10 kJ mol-1 in file solid state. This is surprising because the monoamine has a nonzero dipole moment and a molecular structure that allows forformation of linear arrays of intermolecularly N H—C hydrogen-bonded molecules in the crystal, while file other species have zero dipoles and lack the possibility of such stabilization... 

It is not surprising therefore that force-fields directed at hydrogen-bonded molecules have favored tiie simpler charge-charge formula,... 

In p-isosparteine (14) all rings have a chairlike shape (54). Protonation of the N-16 atom makes the distance between N-1 and N-16 equal to 2.61 A, owing to the presence of an intramolecular hydrogen bond. Molecules of sparteine stereoisomers in crystals are sterically conjugated, and in all cases the angles between atoms C-6—C-7—C-17 and C-10—C-9—C-11 were increased to 116-120° (42-50). The B and C rings are flattened at their N termini as a result of noncovalent interaction of atoms with those situated next to them. The conformation of such strained molecules is stabilized by intramolecular hydrogen bonds (46). 

Hydrogen-bonded Molecules held Low melting insulators H2O (ice) 50... 

AN INTERPRETATION OF THE BREADTH OF THE HYDROGEN STRETCHING BANDS IN THE SPECTRA OF HYDROGEN BONDED MOLECULES... 

However, the limitation of the mathematical analysis to three atoms is not justified, since the polarization will certainly be transmitted to the remaining part of a hydrogen-bonded molecule. Thus, in the examples of the dimeric carboxylic acid or o-mtrosophenol, once one assumes a contribution by the wave function of the structures... 

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