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A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any species that has a filled orbital containing an electron pair which is not involved in bonding but may ...
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]
9-borafluorenes are highly Lewis acidic at the boron center and readily form Lewis acid-base adducts to satisfy the octet for the boron atom. In these adducts, the boron center is no longer trigonal planar and no longer has its empty p orbital that participates in conjugation in the π system in 9-borafluorene.
Boron trifluoride is a versatile Lewis acid that forms adducts with such Lewis bases as fluoride and ethers: CsF + BF3 → Cs [BF4] O (CH 2 CH 3) 2 + BF3 → BF3·O (CH2CH3)2. Tetrafluoroborate salts are commonly employed as non-coordinating anions.
ECW model. In chemistry, the ECW model is a semi-quantitative model that describes and predicts the strength of Lewis acid – Lewis base interactions. Many chemical reactions can be described as acid–base reactions, so models for such interactions are of potentially broad interest. The model initially assigned E and C parameters to each and ...
Non-nucleophilic. Weak. v. t. e. 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] The discovery that some FLPs split H 2[4 ...
As delocalisation of the 4π electrons is prevented by antiaromaticity, the unsaturated boron atom has low occupancy of its vacant p z orbital and is highly Lewis acidic. Along with the low energy LUMO, boroles show an inherent propensity to form Lewis acid–base adducts even with substrates of low donor strengths. Natural Bonding Orbitals of ...
In chemistry, phosphine-boranes are organophosphorus compounds with the formula R 3−n H n PBH 3. They are Lewis acid-Lewis base adducts derived from organophosphines (PR 3−n H n) and borane (BH 3 ). They are generally colorless or white solids. Since these adducts are air-stable, they represent a protected form of the parent organophosphine.