Hydrogen-bond donors interactions with acceptors

Its hydroxyl group is a hydrogen bond donor and a hydrogen bond acceptor, interacting with a large variety of polar groups of different solutes. 

An H-polar fragment is one that can be expected to participate in hydrogen bonding, either as a donor or an acceptor, such as -NH, - OH, -0-, and -COjH. For such fragments a factor may have to be added that takes into account hydrogen bonding or interactions with nearby halogens. 

ILs can act as both hydrogen bond acceptors (anions) and donors (cations), and as expected, they interact with substances with both acceptor and donor sites. In particular, 1,3-dialkylimidazolium ILs can dissolve a plethora of classical polar and non-polar compounds. All 1,3-dialkylimidazolium ILs reported to date are hygroscopic, and their miscibility with water is largely controlled by the nature of the anion. While salts containing nitrate, chloride, and perchlorate anions are usually miscible with water in all compositions, those associated with hexafluorophosphate and bis(trifluoromethane) sulfonylamidate anions are almost completely immiscible with water.It is also known that an increase in the A-alkyl chain length increases the hydrophobicity for a series of l-alkyl-3-methylimidazolium hexafluorophosphate ILs." The miscibility of water in ILs can be increased by the addition of short-chain alcohols or lowered by the addition of salts (salting-out effect). ... 

The unified scale of solvent polarities was expanded to include the very important class of polar hydrogen bonding solvents. Since these solvents are capable of undergoing both non-specific and specific donor-acceptor interactions with donor solute probes, the above equation modifies to ... 

Figure C3.2.7. A series of electron transfer model compounds with the donor and acceptor moieties linked by (from top to bottom) (a) a hydrogen bond bridge (b) all sigma-bond bridge (c) partially unsaturated bridge. Studies with these compounds showed that hydrogen bonds can provide efficient donor-acceptor interactions. From Piotrowiak P 1999 Photoinduced electron transfer in molecular systems recent developments Chem. Soc. Rev. 28 143-50.

AB The molecules belonging to the last category are equipped with both the acidic and the basic functionalities and, hence, they can interact through the hydrogen bonds both as proton donors and proton acceptors. Acohols and carboxylic acids are among the most representative examples from this group. 

Prausnitz and coworkers [91,92] developed a model which accounts for nonideal entropic effects by deriving a partition function based on a lattice model with three categories of interaction sites hydrogen bond donors, hydrogen bond acceptors, and dispersion force contact sites. A different approach was taken by Marchetti et al. [93,94] and others [95-98], who developed a mean field theory... 

In summary, we can say that, because of the unique absence of angular and radial nodes in the H-atom valence shell, the hydride oah orbital is uniquely suited to strong n-a donor-acceptor interactions with Lewis bases. In turn, the unique energetic and angular features of nB-aAH interactions (or equivalently, of B H—A <—> B—H+ A covalent-ionic resonance) can be directly associated with the distinctive structural and spectroscopic properties of B - H—A hydrogen bonding. 

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