Lewis acid

Examples of Lewis acid in the following topics:

• Lewis Acid and Base Molecules

  • Lewis bases are electron-pair donors, whereas Lewis acids are electron-pair acceptors.
  • A Lewis acid is defined as an electron-pair acceptor, whereas a Lewis base is an electron-pair donor.
  • A Lewis base, therefore, is any species that donates a pair of electrons to a Lewis acid.
  • In organic chemistry, it is useful to understand that nucleophiles are Lewis bases and electrophiles are Lewis acids.
  • We first look at the Bronsted-Lowry theory, and then describe Lewis acids and bases according to the Lewis Theory.

• Metal Cations that Act as Lewis Acids

  • Transition metals can act as Lewis acids by accepting electron pairs from donor Lewis bases to form complex ions.
  • Ligands create a complex when forming coordinate bonds with transition metals ions; the transition metal ion acts as a Lewis acid, and the ligand acts as a Lewis base.
  • Usually, metal complexes can only serve as Lewis acids after dissociating from a more weakly bound Lewis base, often water.
  • Nearly all compounds formed by the transition metals can be viewed as collections of the Lewis bases—or ligands—bound to the metal, which functions as the Lewis acid.
  • All these metals act as Lewis acids, accepting electron pairs from their ligands.

• Acid-Base Reactions

  • According to the Lewis theory, an acid is an electron pair acceptor, and a base is an electron pair donor.
  • Lewis bases are also Brønsted bases; however, many Lewis acids, such as BF3, AlCl3 and Mg2+, are not Brønsted acids.
  • Carbocations are also Lewis acids, as the reverse reaction demonstrates.
  • A terminology related to the Lewis acid-base nomenclature is often used by organic chemists.
  • Here the term electrophile corresponds to a Lewis acid, and nucleophile corresponds to a Lewis base.

• Trihalides: Boron-Halogen Compounds

  • Trihalides adopt a planar trigonal structure and are Lewis acids.
  • The trihalides form planar trigonal structures and are Lewis acids because they readily form adducts with electron-pair donors, which are called Lewis bases.
  • Their relative Lewis acidities can be evaluated in terms of the relative exothermicities of the adduct-forming reaction.
  • Such measurements have revealed the following sequence for the Lewis acidity: BF3 < BCl3 < BBr3 (in other words, BBr3 is the strongest Lewis acid).
  • In an alternative explanation, the low Lewis acidity for BF3 is attributed to the relative weakness of the bond in the adducts F3B-L.

• Nature of Acids and Bases

  • Common examples of acids include acetic acid (in vinegar), sulfuric acid (used in car batteries), and tartaric acid (used in baking).
  • Lewis acid: any substance that can accept a pair of electrons.
  • sulfuric acid (H2SO4; only the first proton is considered strongly acidic)
  • A list of various Lewis bases (right) and Lewis acids (left).
  • In this video I introduce to you guys what the heck an Acid and Base really is forgetting the Lewis or Bronstead/Lowry definitions and then we'll go more in depth in parts 2,3, and 4.

• Salts that Produce Acidic Solutions

  • When dissolved in water, acidic salts form solutions with pH less than 7.0.
  • This is due either to the presence of a metal cation that acts as a Lewis acid (which will be discussed in a later concept), or, quite commonly, due to a hydrolyzable proton in the cation or the anion.
  • Acid salts can also contain an acidic proton in the anion.
  • Examples of anions with an acidic proton include:
  • Anilinium chloride is an example of an acid salt.

• The Brønsted-Lowry Definition of Acids and Bases

  • A wide range of compounds can be classified in the Brønsted-Lowry framework: mineral acids and derivatives such as sulfonates, carboxylic acids, amines, carbon acids, and many more.
  • The conjugate acid is the species that is formed when the Brønsted base accepts a proton from the Brønsted acid.
  • Here, acetic acid acts as a Brønsted-Lowry acid, donating a proton to water, which acts as the Brønsted-Lowry base.
  • Chemistry 12.1 What are Acids and Bases?
  • We first look at the Brønsted-Lowry theory, and then describe Lewis acids and bases according to the Lewis Theory

• The Leveling Effect

  • In Lewis basic (or acidic) solutions, the effect of a solvent to place a maximum level on the acidity or basicity of an acid or base.
  • The leveling effect, or solvent leveling, is an effect that places an upper-limit on the strength of an acid (or base) in a given solvent when the solvent is Lewis acidic or Lewis basic.
  • Similarly a weak acid has less tendency to donate protons than a strong acid.
  • As a result, a strong acid (such as perchloric acid) exhibits more strongly acidic properties than a weak acid (such as acetic acid) when dissolved in a weakly basic solvent.
  • Strong bases are leveling solvents for acids, weak bases are differentiating solvents for acids.

• Oxoacids

  • Halogen oxoacids include hypochlorous acid (HOCl); chlorous acid(HOClO); chloric acid(HOClO2); oerchloric acid(HOClO3); oerbromic acid (HOBrO3)
  • Consider the simple oxyacids HOI (hypoiodous acid), HOBr (hypobromous acid), and HOCl (hypochlorous acid).
  • Carboxylic acids are the most common type of organic acid.
  • Mellitic acid is an example of a hexacarboxylic acid.
  • Carboxylic acids can be seen as reduced or alkylated forms of the Lewis acid carbon dioxide; under some circumstances they can be decarboxylated to yield carbon dioxide.

• Introduction to Lewis Structures for Covalent Molecules

  • The Lewis formalism used for the H2 molecule is H:H or H—H.
  • The resulting molecule that is formed is F2, and its Lewis structure is F—F.
  • We have looked at how to determine Lewis structures for simple molecules.
  • The Lewis structure for carbon dioxide, CO2, is a good example of this.
  • Acetic acid, CH3COOH, can be written out with dots indicating the shared electrons, or, preferably, with dashes representing covalent bonds.