Search results
Results From The WOW.Com Content Network
A Lewis base, then, is any species that has a filled orbital containing an electron pair which is not involved in bonding but may form a dative bond with a Lewis acid to form a Lewis adduct. For example, NH 3 is a Lewis base, because it can donate its lone pair of electrons.
An alternative quantitative measure is the heat of formation of the Lewis acid-base adduct in a non-coordinating solvent. The ECW model is quantitative model that describes and predicts the strength of Lewis acid base interactions, -ΔH . The model assigned E and C parameters to many Lewis acids and bases.
A good example is the formation of adducts between the Lewis acid borane and the oxygen atom in the Lewis bases, tetrahydrofuran (THF): BH 3 ·O(CH 2) 4 or diethyl ether: BH 3 ·O(CH 3 CH 2) 2. Many Lewis acids and Lewis bases reacting in the gas phase or in non-aqueous solvents to form adducts have been examined in the ECW model. [3]
The enthalpies of formation of some Donor-I 2 adducts are listed below. I 2 is a Lewis acid classified as a soft acid and its acceptor properties are discussed in the ECW model. The relative acceptor strength of I 2 toward a series of bases, versus other Lewis acids, can be illustrated by C-B plots. [15]
A frustrated Lewis pair (FLP) is a compound or mixture containing a Lewis acid and a Lewis base that, because of steric hindrance, cannot combine to form a classical adduct. [1] Many kinds of FLPs have been devised, and many simple substrates exhibit activation. [2] [3]
Adducts involving metal ions are usually described as coordination complexes. [13] According to the original formulation of Lewis, when a neutral base forms a bond with a neutral acid, a condition of electric stress occurs. [7] The acid and the base share the electron pair that formerly belonged to the base. [7]
B(C 6 F 5) 3 forms a strong Lewis adduct with water, [5] which was shown to be a strong Brønsted acid having an acidity comparable to hydrochloric acid (in acetonitrile). [6] In consequence, even traces of moisture are able to deactivate B(C 6 F 5) 3 and remaining catalytic activity might only be due to the Brønsted acidity of the water adduct.
In chemistry a donor number (DN) is a quantitative measure of Lewis basicity.A donor number is defined as the negative enthalpy value for the 1:1 adduct formation between a Lewis base and the standard Lewis acid SbCl 5 (antimony pentachloride), in dilute solution in the noncoordinating solvent 1,2-dichloroethane with a zero DN.