How Organic Reactions Occur:Mechanisms Two ways a covalent two-electron bond can form: 1.Symmetrical -One electron is donated to the new bond by each reactant (radical) A· A:B 2.Unsymmetrical Both bonding electrons are donated by one reactant(polar) A A:B Two ways a covalent two-electron bond can form: 1. Symmetrical ▪ One electron is donated to the new bond by each reactant (radical) 2. Unsymmetrical ▪ Both bonding electrons are donated by one reactant (polar) How Organic Reactions Occur: Mechanisms