Lewis Acids and Bases - Lewis Acids

Lewis Acids

Lewis acids are diverse. Simplest are those that react directly with the Lewis base. But more common are those that undergo a reaction prior to forming the adduct.

• Examples of Lewis acids based on the general definition of electron pair acceptor include:
  • the proton (H+) and acidic compounds onium ions, such as NH₄+ and H₃O+
  • metal cations, such as Li+ and Mg2+, often as their aquo or ether complexes,
  • trigonal planar species, such as BF₃ and carbocations H₃C+
  • pentahalides of phosphorus, arsenic, and antimony
  • electron poor π-systems, such as enones and tetracyanoethylene

Again, the description of a Lewis acid is often used loosely. For example, in solution, bare protons do not exist.