Lewis base examples

Any chemical species having a vacant orbital and thus acting as an electron-pair acceptor from a Lewis base. Examples of Lewis acids include BF3, Fe +, Na, Ca, and SO3. See Lewis Base Acidity Lewis Acidity... 

A Lewis acid is an electron-pair acceptor and a Lewis base is an electron-pair donor. Lewis acids include not only H+ but also other cations and neutral molecules that can accept a share in a pair of electrons from a Lewis base. Examples of Lewis acids are Al3+, Cu2+, BF3, SO3, and C02. 

Solvent Class Dielectric Constant Brpnsted and/or Lewis Acid Brpnsted and/or Lewis Base Examples... 

Identifying Lewis acid and base species Given a reaction involving the donation of an electron pair, identify the Lewis acid and the Lewis base. (EXAMPLE 16.2)... 

Oxides of metals -> Called basic oxides -> Tend to act as Lewis bases Examples Na20, MgO, CaO -> React with water to form Bronsted bases Example CaO(s) + H20(l) - Ca(OH)2(aq)... 

Towards a simple Lewis base, for example the proton, phosphine is a poorer electron donor than ammonia, the larger phosphorus atom being less able to form a stable covalent bond with the acceptor atom or molecule. Phosphine is, therefore, a much weaker base than ammonia and there is no series of phosphonium salts corresponding to the ammonium salts but phosphonium halides. PH4X (X = Cl, Br, I) can be prepared by the direct combination of phosphine with the appropriate hydrogen halide. These compounds are much more easily dissociated than ammonium halides, the most stable being the iodide, but even this dissociates at 333 K PH4I = PH3 -t- HI... 

Finally, the solvent also interacts with sites of the Lewis acid and the Lewis base that are not directly involved in mutual coordination, thereby altering the electronic properties of the complex. For example, delocalisation of charges into the surrounding solvent molecules causes ions in solution to be softer than in the gas phase . Again, water is particularly effective since it can act as an efficient electron pair acceptor as well as a donor. 

The product of this reaction a Lewis acid Lewis base complex called informally boron tnfluonde etherate may look unusual but it is a stable species with properties different from those of the reactants Its boiling point (126°C) for example is much higher than that of boron tnfluonde—a gas with a boiling point of — 100°C—and diethyl ether a liquid that boils at 34°C... 

The Lewis base that acts as the nucleophile often is but need not always be an anion Neutral Lewis bases can also serve as nucleophiles Common examples of substitutions involving neutral nucleophiles include solvolysis reactions Solvolysis reactions are substitutions m which the nucleophile is the solvent m which the reaction is carried out 8olvolysis m water (hydrolysis) converts an alkyl halide to an alcohol... 

Tertiary alkyl halides are so sterically hindered to nucleophilic attack that the pres ence of any anionic Lewis base favors elimination Usually substitution predominates over elimination m tertiary alkyl halides only when anionic Lewis bases are absent In the solvolysis of the tertiary bromide 2 bromo 2 methylbutane for example the ratio of substitution to elimination is 64 36 m pure ethanol but falls to 1 99 m the presence of 2 M sodium ethoxide... 

In a complexation reaction, a Lewis base donates a pair of electrons to a Lewis acid. In an oxidation-reduction reaction, also known as a redox reaction, electrons are not shared, but are transferred from one reactant to another. As a result of this electron transfer, some of the elements involved in the reaction undergo a change in oxidation state. Those species experiencing an increase in their oxidation state are oxidized, while those experiencing a decrease in their oxidation state are reduced, for example, in the following redox reaction between fe + and oxalic acid, H2C2O4, iron is reduced since its oxidation state changes from -1-3 to +2. 

In Group 14 (IV), carbon serves as a Lewis base in a few of its compounds. In general, saturated ahphatic and aromatic hydrocarbons are stable in the presence of BF, whereas unsaturated ahphatic hydrocarbons, such as propjdene or acetylene, are polymerized. However, some hydrocarbons and their derivatives have been reported to form adducts with BF. Typical examples of adducts with unsaturated hydrocarbons are 1 1 adducts with tetracene and 3,4-benzopyrene (39), and 1 2 BF adducts with a-carotene and lycopene (40). 

For main group elements the number of framework electrons contributed is equal to (t + a — 2) where v is the number of valence shell electrons of that element, and x is the number of electrons from ligands, eg, for Ff, x = and for Lewis bases, x = 2. Examples of 2n + 2 electron count boranes and heteroboranes, and the number of framework electrons contributed by their skeletal atoms, ate given in Table 1. 

These isomerization processes may be dependent on the nature of the solvent. For example, the rotational barrier of the tetrazathiapentalenes 15.15 (ca. 16 kcal moF ) is influenced by the donor or acceptor ability of the substituents X and Y through the S N short contacts.Solvents with acidic protons increase the magnitude of the barrier, whereas solvents that are good Lewis bases decrease the size of the barrier, owing to solvation of the transition state. 

Alternatively, within the Lewis formalism, acids are fluoride-ion acceptors. The prime examples are AsF- and SbFs (which give MF ) and to a lesser extent BF3 which yields BF4 ". A greater diversity is found amongst Lewis bases (fluoride-ion donors), typical examples being XeFg, SF4, CIF3 and BrF3 ... 

This last reaction is typical of many in which F3CIO can act as a Lewis base by fluoride ion donation to acceptors such as MF5 (M = P, As, Sb, Bi, V, Nb, Ta, Pt, U), M0F4O, Sip4, BF3, etc. These products are all white, stable, crystalline solids (except the canary yellow PtFe ) and contain the [F2CIO] cation (see Fig. 17.26h) which is isostructural with the isoelectronic F2SO. Chlorine trifluoride oxide can also act as a Lewis acid (fluoride ion acceptor) and is therefore to be considered as amphoteric (p. 225). For example KF, RbF and CsF yield M [F4C10] as white solids whose stabilities increase with increasing size of M+. Vibration spectroscopy establishes the C4 structure of the anion (Fig. 17.29g). 

Free borane (2) exists as gaseous dimer—the diborane BaHg. In addition Lewis acid/Lewis base-complexes, as for example formed in an ethereal solvent, e.g. 4, are commercially available ... 

The fact that a Lewis acid is able to accept an electron pair means that it must have either a vacant, low-energy orbital or a polar bond to hydrogen so that it can donate H+ (which has an empty7 Is orbital). Thus, the Lewis definition of acidity includes many species in addition to H+. For example, various metal cations, such as Mg2+, are Lewis acids because they accept a pair of electrons when they form a bond to a base. We ll also see in later chapters that certain metabolic reactions begin with an acid-base reaction between Mg2+ as a Lewis acid and an organic diphosphate or triphosphate ion as the Lewis base. 

Notice in the list of Lewis bases just given that some compounds, such as carboxylic acids, esters, and amides, have more than one atom ivith a lone pair of electrons and can therefore react at more than one site. Acetic acid, for example, can be protonated either on the doubly bonded oxygen atom or on the singly bonded oxygen atom. Reaction normally occurs only once in such instances, and the more stable of the two possible protonation products is formed. For acetic add, protonation by reaction with sulfuric acid occurs on... 

Before beginning a detailed discussion of alkene reactions, let s review briefly some conclusions from the previous chapter. We said in Section 5.5 that alkenes behave as nucleophiles (Lewis bases) in polar reactions. The carbon-carbon double bond is electron-rich and can donate a pair of electrons to an electrophile (Lewis acid), for example, reaction of 2-methylpropene with HBr yields 2-bromo-2-methylpropane. A careful study of this and similar reactions by Christopher Ingold and others in the 1930s led to the generally accepted mechanism shown in Figure 6.7 for electrophilic addition reactions. 

Nucleophilicity roughly parallels basicity when comparing nucleophiles that have the same reacting atom. For example, OH- is both more basic and more nucleophilic than acetate ion, CH3CO2-, which in turn is more basic and more nucleophilic than H20. Since "nucleophilicity" is usually taken as the affinity of a Lewis base for a carbon atom in the Sfj2 reaction and "basicity" is the affinity of a base for a proton, it s easy to see why there might be a correlation between the two kinds of behavior. 

Leuprolide, structure of, 1056 I.evorotatory, 295 Lewis, Gilbert Newton. 8 Lewis acid, 57-58 examples of, 58 reactions of, 57-58 Lewis base, 57, 59-60 examples of, 59 reactions of, 59-60 Lewis structure, 9 resonance and, 43 Lexan, structure and uses of, 819,... 

To remove an ion, we can use the fact that many metal cations are Lewis acids (Section 10.2). When a Lewis acid and a Lewis base react, they form a coordinate covalent bond and the product is called a coordination complex. In this section, we consider complexes in which the Lewis acid is a metal cation, such as Ag+. An example is the formation of Ag(NI 1,)2+ when an aqueous solution of the Lewis base ammonia is added to a solution of silver ions ... 

Ammonia is very soluble in water because the NH3 molecules can form hydrogen bonds to H20 molecules. Ammonia is a weak Bronsted base in water it is also a reasonably strong Lewis base, particularly toward d-block elements. For example, it reacts with Cu2+(aq) ions to give a deep-blue complex (Fig. 15.4) ... 

Water is also a Lewis base, because an HzO molecule can donate one of its lone pairs to a Lewis acid and form complexes such as Fe(H20)63+. Water s ability to act as a Lewis base is also the origin of its ability to hydrolyze substances. The reaction between water and phosphorus pentachloride mentioned in Section 15.2 is an example. 

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