Hydrogen antidromic

The water molecules form polymeric chains which include homodromic and antidromic six-membered hydrogen-bonded circles each one of the water species is either threefold or fourfold coordinated, donating at least one H-bond to the surface of a neighboring bilayer. 

Cooperative, Homodromic, and Antidromic Hydrogen-Bonding Patterns in the a-Cyclodextrin Hydrates... 

A predominant motif in the hydrogen-bonding structure in a-cyclodex-trin-7.57H20 is a ribbon of fused four- and six-membered antidromic cycles, shown in Figs. 18.5 c and 18.7 c, d. This is generated by the symmetry operation of a screw axis in the b direction. It contains an infinite chain of water molecules,... 

Fig. 18.7a-e. Cyclic and chain-like hydrogen-bonding patterns O-H- -O observed in a a-cyclo-dextrin-6H20, form I b a-cyclodextrin 6 H20, form II , intramolecular c,d,e a-cyclodextrin-7.57 H20. Infinite homodromic chains are marked chain, and cycles are indicated by round arrows with one (homodromic) and two (antidromic) heads. Only atoms of water molecules and of hydroxyl groups are drawn, the former denoted by W and the latter by the nomenclature described in Fig. 18.1. Each of the pictures a to e shows only a section of the respective crystal structure [78, 109, 575]...

Hydrogen-bonding patterns in crystal structures of the cydodextrins and the simpler carbohydrates differ. The infinite, homodromic chains are common both in the low molecular-weight carbohydrates and in the cydodextrins. The principal difference lies in the frequency of occurrence of the homodromic and antidromic cycles, which are common in the cyclodextrin crystal structures and rare in the mono-, di-, and trisaccharides. The cyclic patterns are the rule in the clathrate hydrates and in the ices. From this point of view, the hydrogen-bonding patterns of the hydrated cydodextrins lie between those of the simpler hydrated carbohydrates and those of the hydrate inclusion compounds, discussed in Part IV, Chapter 21. 

These calculations also predict that the formation of chains or cycles of O-H - 0 hydrogen bonds causes polarization such that the charges on oxygen become more negative while those on the hydrogen atoms become more positive (Thble 18.3). The polarization is calculated to be greater for homodromic than for antidromic arrangements. 

Fig. 21.10. The buckled hydrate layer in pyridine 3H20, with hydrogen-bonding geometry indicated. Note that the hydrogen-bonding pattern is homodromic in the hexagon and antidromic in the pentagon and quadrilateral. Pyridine molecules are stacked above and below this layer in nearly vertical orientation to the layer and bound to it by 0(2)-H -N hydrogen bonds (not shown) [793]...

Fig. 21.16. Section of the crystal structure of 2,5-dimethyl-2,5-hexanediol-4H20. Oxygen atoms are drawn black, carbon and hydrogen atoms as large and small circles, respectively. Note the homodromic infinite chains running in opposite directions and linked in the form of antidromic pentagons [817]...

Fig. 2-4a. Three types of circular hydrogen bonds (a) homodromic, (b) antidromic, and (c) heterodromic hydrogen bonds [193].

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