Hydrogen-bonded dimmers

O. Galvez, P. C. Gomez and L. F. Pacios, Variation with the intermolecular distance of properties dependent on the electron density in hydrogen bond dimmers, J. Chem. Phys. 115, 11166-11184(2001). 

Olanzapine appears to exist in at least five polymorphic forms, and the structure of Form II has been reported [32]. Two molecules form centrosymmetric dimmers stabilized by a series of C—H - rc interactions, and the dimmers are connected by a system of intermolecular N—C—and C—H S hydrogen bonds. The structure of a monoclinic polymorph of isoxsuprine hydrochloride has been reported [33], The molecular conformation existing in the new monoclinic polymorph was found to be very similar to that existing in the known triclinic polymorph. 

TABLE 14. Energetic and structural parameters for three ammonia dimmers (29, 28 and 31) as calculated ab initio (6-31G + BSSE correction), by the original MM3 force field (MM3) and by MM3 augmented with a directional hydrogen bonding potential function (MM3-94)°. Reproduced by permission... 

The first member on the right in expression (38) is the relaxation rate caused by dimmers of the pure material. The second member arises from dynamics of the benzoic acid dimers contained within the range of the thiondigo quest molecule 7j-1 (ffl) is stipulated by modulation of proton dipolar interaction induced by the proton transfer in the hydrogen bonds. 

Figure 2 Example of planar projection of one of the configurations of an ortho-para PF dimmer on the surface of a schematic cellulose crystallite showing a phenolic dimmer (a dihydroxy diphenyl methane) conformation of minimal energy and main dimer-cellulose hydrogen bonding. (From Ref. 8.)... 

The high m.p. and b.p. of p3rrazole compared with 1-alkyl or aryl substituted pyrazoles are due to intermolecular hydrogen bonding which results in the dimmer. It is a tautomeric substance. Pyrazole is a weak basic and forms salts with inorganic adds the imino hydrogen... 

Quantum chemical calculations (with consideration of the effects of a solvent) of water clusters (HjO) at = 1, 2,4, 6 in cyclohexene (as a model nonpolar medium) show that the free energy of solvation is minimal for a dimmer in which 75% of protons do not participate in the hydrogen bonds and 8h=0.8-1.9 ppm corresponding to signal 2. These calculations show a possible reason for the appearance of the aforementioned signal for bone tissue. 

Morita, S. and Nagakura, S., Near-infrared spectra of hydrogen-bonded cyclic dimmers of some carboxylic acids, J. Mol. Spectrosc., 41, 54—68, 1972. 

In a similar way, chemically induced dimmer configuration prepared on the silicon Si(l 0 0) surface is essentially untitled and differs, both electronically and structurally, from the dynamically tilting dimers normally found on this surface [71]. The dimer units that compose the bare Si(l 0 0) surface tilt back and forth in a low-frequency ( 5 THz) seesaw mode. In contrast, dimers that have reacted with H2 have their Si—Si dimer bonds elongated and locked in the horizontal plane of the surface. They are more reactive than normal dimers. For molecular hydrogen (H2) adsorption, the enhancement is even 10 at room temperature. In a similar way, boundaries between crystaUites and amorphous regions seem to be active sites of chain adsorption on CB surface. CB nanoparticles can be understood as open quantum systems, and the uncompensated forces can be analyzed in terms of quantum decoherence effects [70]. The dynamic approach to reinforcement proposed in this chapter becomes an additional support in epistemology of it, and with data from sub-nanolevel. 

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