Electron-pair acceptors donation

We have seen that a base can be defined as combining with a proton and, therefore, requires at least one lone pair of electrons. A more general definition of acids and bases, due to G. N. Lewis, describes a base as any species (atom, ion or molecule) which can donate an electron pair, and an acid as any species which can accept an electron pair— more simply, a base is an electron-pair donor, an acid an electron-pair acceptor. Some examples of Lewis acids and bases are ... 

Achiral (Section 7 1) Opposite of chiral An achiral object is supenmposable on its mirror image Acid According to the Arrhenius definition (Section 1 12) a substance that ionizes in water to produce protons Accord mg to the Br0nsted-Lowry definition (Section 1 13) a sub stance that donates a proton to some other substance According to the Lewis definition (Section 1 17) an electron pair acceptor... 

It was G. N. Lewis who extended the definitions of acids and bases still further, the underlying concept being derived from the electronic theory of valence. It provided a much broader definition of acids and bases than that provided by the Lowry-Bronsted concept, as it furnished explanations not in terms of ionic reactions but in terms of bond formation. According to this theory, an acid is any species that is capable of accepting a pair of electrons to establish a coordinate bond, whilst a base is any species capable of donating a pair of electrons to form such a coordinate bond. A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. These definitions of acids and bases fit the Lowry-Bronsted and Arrhenius theories, and cover many other substances which could not be classified as acids or bases in terms of proton transfer. 

We should note that the formation of this bond confers formal charges on the B and N atoms. In this bond and many similar Lewis acid-base complexes both the electrons forming the bond come from the same atom rather than from different atoms, as in the formation of a bond between two chlorine atoms. This type of bond is often called a donor-acceptor bond, a dative bond, or a coordinate bond, and is sometimes given a special symbol—an arrow denoting the direction in which the electron pair is donated ... 

Coordination compounds are also known as coordination complexes, complex compounds, or simply complexes. The essential feature of coordination compounds is that coordinate bonds form between electron pair donors, known as the ligands, and electron pair acceptors, the metal atoms or ions. The number of electron pairs donated to the metal is known as its coordination number. Although many complexes exist in which the coordination numbers are 3, 5, 7, or 8, the majority of complexes exhibit coordination numbers of 2, 4, or 6. 

Thus, by definition, electrophiles are electron-pair acceptors and nucleophiles are electron-pair donors. These definitions correspond closely to definitions used in the generalized theory of acids and bases proposed by G. N. Lewis (1923). According to Lewis, an acid is any substance that can accept an electron pair, and a base is any substance that can donate an electron pair to form a covalent bond. Therefore acids must be electrophiles and bases must be nucleophiles. For example, the methyl cation may be regarded as a Lewis acid, or an electrophile, because it accepts electrons from reagents such as chloride ion or methanol. In turn, because chloride ion and methanol donate electrons to the methyl cation they are classified as Lewis bases, or nucleophiles ... 

During the collision of two polymer grains areas with a size of a few square micrometers come into contact. In the contact zone an electron transfer can take place as described in [2] (Fig. 2a). In case of the collision of two chemically different polymer particles one of them preferably interacts as electron pair donator and the other species as electron pair acceptor. In this way laterally expanded charge domains can be formed (Fig. 2b). The low electrical conductivity of the polymer bulk and surface prevents a rapid charge dissipation, hence the formed domain structure seems to be permanently stable. 

Fig. 2 Model concept of the contact charging of polymer grains, a Contact between an electron pair donator domain (empty dots) of the particle 1 and an electron pair acceptor domain (grey dots) of the particle 2. Charge transfers (e-) are taking place. After separation the two particles (b), a positively charged ( ) and a negative charged ( ) domain, remain on the particles surface...

According to the Lewis theory of acids and bases (to be discussed in detail in Chapter 5), an acid is an electron pair acceptor and a base is an electron pair donor. Accordingly, the following reactions are acid-base reactions because they represent processes in which electron pair donation and acceptance occurs ... 

In 1923 G. N. Lewis" proposed a definition of acid-base behavior in terms of electron-pair donation and acceptance. The Lewis definition is perhaps the most widely used of all because of its simplicity and wide applicability, espeaally in the field of organic reactions. Lewis defined a base as cn electron-pair donor and an acid as an electron-pair acceptor. In addition to all of llie reactions discussed above, the Lewis definition includes reactions in which no ions are formed and no hydrogen ions or other ions are transferred 2... 

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],... 

This paper reviews the chemistry of metalloborane derivatives that contain borane or heteroatom borane groups which function as monohapto ligands. These compounds can be divided into three classes according to the number of electrons formally donated by the borane ligand to the metal. The electron pair acceptor class, represented by the compound Na[(OC)5Mn BHg], has received little attention thus far. The one-electron donor class, exemplified by the complex, l,2-(CH3)2-3- (C5H5)Fe(CO)2]-BioC2Ho, has a rich chemistry of metal-carbon and metal-boron derivatives. The third class includes two-electron donor derivatives that are represented by the compound (CHs)f,N[7,8-BoHioCHP - CrfCO),]. 

Perhaps you will not be surprised, then, you to learn that an even more general model of acids and bases was proposed by American chemist G. N. Lewis (1875-1946). Recall that Lewis developed the electron-pair theory of chemical bonding and introduced Lewis structures to keep track of the electrons in atoms and molecules. He applied his electron-pair theory of chemical bonding to acid-base reactions. Lewis proposed that an acid is an ion or molecule with a vacant atomic orbital that can accept (share) an electron pair. A base is an ion or molecule with a lone electron pair that it can donate (share). According to the Lewis model, a Lewis acid is an electron-pair acceptor and a Lewis base is an electron-pair donor. Note that the Lewis model includes all the substances classified as Bronsted-Lowry acids and bases and many more. 

Substitution reactions, which occur in all areas of chemistry, are those in which an atom or group of atoms is substituted for another. A Lewis base is an electron pair donor, and a Lewis acid is an electron pair acceptor. Some common Lewis bases are H2O, NH3, OH , F , etc., while some common Lewis acids are AICI3, BCI3, carbocations (RsC ), etc. In a Lewis acid-base reaction, a coordinate bond is formed between the acid and base with the base donating the pair of electrons. Lewis bases are known as nucleophiles and Lewis acids are known as electrophiles. In fact, when A is a... 

A Lewis acid is an electron pair acceptor and a Lewis base is an electron pair donator. A complex is formed when a Lewis acid and a Lewis base share a pair of elecfrons and form a bond. When an organic compound is used as a ligand in a complex formation with a metal it acts as a Lewis acid and the combination in many cases produces real acids. This means that the metal Lewis bases compete with the acidic "loose protons" for the sharing electron and will be replaced by the proton at pH values that are low compared to the pKa of the ligand in question. The metals of the d block, on the otiier hand, are known for forming insoluble hydroxides or oxides at neutrality or high pH. So a complex is often stable only inside Ihe pH interval between ligand deprotonation and metal hydroxide precipitation. 

---