Donor-acceptor pairing hydrogen bonding

Of course, unlike a hydroxyl group, fluorine cannot be a hydrogen bond donor, (Fig. 3). Furthermore, it is a poor acceptor of hydrogen bonds despite its strong electronegativity and its lone pairs of electrons. This is mainly due to the low polarisability of its electron pairs, which thus contribute only weakly to the electron transfer [5,13,20,21]. 

We have formed many donor/acceptor pairs which preferentially hydrogen bond to one another in the presence of nitro or aniline groups, and which form polar hydrogen-bonded chains. These pairs are shown in Table ID. 

The term hydrogen-bond acceptor (HBA) refers to the acceptance of the proton of a hydrogen-bond. Therefore, HBA solvents are also electron-pair donor (EPD) solvents. Hydrogen-bond donor (HBD) refers to the donation of the proton. Therefore, HBD solvents behave as protic solvents. 

Pirkle-type phases are amino acid derivatives possessing an aromatic entity which can undergo n-n interactions with the solute. The aromatic entity can be either a n donor or n acceptor. The CSP and the solute form a n donor/acceptor pair. This complex is then stabilized by additional interactions such as hydrogen bonding, dipole interactions, or steric repulsion [8]. The Pirkle-type phases are most commonly used in normal-phase mode in order to enhance the n-n and hydrogen bond interactions. Hexane with an alcoholic modifier, such as isopropanol, is the mobile phase of choice. These phases have... 

In the context of the foregoing discussion, the hydrogen-bonded donor-acceptor supramolecules of Figure 1 meld the constructs of both inter- and intramolecular electron transfer. From the standpoint of intermolecular electron transfer, these systems represent a preformed precursor complex held together by noncovalent interactions from the standpoint of intramolecular electron transfer, these systems provide a fixed-distance donor-acceptor pair in which charge transport occurs along a noncovalent pathway. 

---