Electron-pair donors

With simple crowns, complex formation may involve various degrees of inclusion of the guest into the cavity of the crown and a conformational rearrangement of the crown is almost always necessary for strong complexation to occur. This will normally involve a redirection of the donor electron pairs on complex formation so that their final orientations optimize a particular host-guest interaction. 

Acids are proton donors (electron-pair acceptors). 

Molecular properties dipole moment, polarizability Chemical properties Acidity (including the abilities as proton donor, hydrogen-bond donor, electron pair acceptor, and electron acceptor)a) ... 

The Lewis acid and Lewis base concept explains the majority of reaction chemistry that we are familiar with. Lewis acid/base reaction chemistry concerns electron pair donors, electron pair acceptor, anions, cations, lone-pairs etc.) [6,7]. 

Radical cations that are produced by electrochemical oxidation are not stable in solvents with appreciable base character. This results because such radicals are subject to attack by available nucleophiles, and solvents that contain donor electron pairs are good nucleophiles. Cation radicals are most stable in solvents that are good Lewis acids and show negligible basic properties. Some of the solvent systems that have been employed to stabilize electrochemically produced cation radicals include nitromethane and nitrobenzene,21 dichloro-methane,22 trifluoroacetic acid-dichloromethane (1 9),23 nitromethane-AlCl3,24 and AlCl3-NaCl (1 l).25 Organic chemists should be familiar with the stabilization of carbonium ions by superacid media.26 These media usually contain fluorosulfuric acid, or mixtures of fluorosulfuric acid with antimony pen-tachloride and sulfur dioxide, and are potent solvents for the production and stabilization of organic cations. 

Klemperer and co-workers. 31) In this model the hydrogen bond is viewed as an electron donor-acceptor complex in which a pair of electrons from the highest occupied molecular orbital of the Lewis base is donated to the lowest unoccupied molecular orbital of the Lewis acid. If the donor electron pair is assumed to have the appropriate hybridization, and the acceptor orbital to be axially symmetric, the above structures can be rationalized as giving maximal overlap between the HOMO and LUMO. 

The chemistry of coordination compounds is a broad area of inorganic chemistry that has as its central theme the formation of coordinate bonds. A coordinate bond is one in which both of the electrons used to form the bond come from one of the atoms, rather than each atom contributing an electron to the bonding pair, particularly between metal atoms or ions and electron pair donors. Electron pair donation and acceptance result in the formation of a coordinate bond according to the Lewis acid-base theory (see Chapter 5). However, compounds such as H3N BC13 will not be considered as coordination compounds, even though a coordinate bond is present. The term molecular compound or adduct is appropriately used to describe these complexes that are formed by interaction of molecular Lewis acids and bases. The generally accepted use of the term coordination compound or coordination complex refers to the assembly that results when a metal ion or atom accepts pairs of electrons from a certain number of molecules or ions. Such assemblies commonly involve a transition metal, but there is no reason to restrict the term in that way because nontransition metals (Al3+, Be2+, etc.) also form coordination compounds. 

Electron-Pair Donor/Electron-Pair Acceptor Interactions (EPD/EPA Interactions) [50-59, 59a, 59b]... 

Molecular polarity of analytes is difficult to quantify unequivocally. The descriptors of polarity are expected to account for differences among the analytes regarding their dipole-dipole, dipole-induced dipole, hydrogen bonding and electron pair donor-electron pair acceptor (EPD-EPA) interactions. To find good descriptors of these chemically specific interactions is difficult, particularly since changes in analyte polarity also affect analyte geometry and its ability to take part in bulkiness-related interactions 7,l2j. 

In this context, interactions between ionic liquids and solutes are understood as intermolecular (and in extension interionic) solvation forces, which can be categorised according to Reichardt [4] (Fig. 2) as non-specific induction and dispersion (Coulomb) forces, and specific directional stoichiometric forces (hydrogen bond acceptor and donor, electron pair acceptor and donor) [4],... 

Charge transfer forces involve the movement of electrons or protons from one molecule to another. Electron pair donor - electron pair acceptor complexes (EPD-EPA) result from the donation of a pair of electrons giving rise to electrostatic attraction between two charged species. The difference between this type of bond and a normal chemical bond is that both bonding electrons are derived from the same molecule (the EPD), the role of the EPA being to provide an empty orbital. It is important not to confuse the EPD-EPA complex with ion pair formation resulting from proton transfer [34],... 

Lewis acid-base theory, electron-pair donor, electron-pair... 

The chemical properties of solvents that are relevant to their dissolution abilities for electrolytes and the ionic dissociation of the latter include their structuredness or self-association and their donor (electron pair donation, basicity) and acceptor (hydrogen bonding ability, acidity) properties as well as their softness. The mutual solubility with other solvents, in particular water, is also of importance as are the windows for making spectroscopic and electrochemical measurements on solutions of ions in the solvents. 

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