> See also: > - [[Chemical Reactions]] # Chemical Reaction Mechanisms **Chemical reactions** involve the breaking and formation of bonds between atoms. Because every bond contains two electrons, there are two potential ways of **bond**: ### Types of Bond Cleavage/Formation **Homolytic cleavage** [[Radical Reactions]] are uncharged chemical species containing a single, **unpaired** electron. **Homolytic Cleavage:** __ ![[Homolytic Cleavage.png|300]] **Heterolytic Cleavage:** __ ![[Heterolytic Cleavage.png|300]] Homolytic cleavage causes the **initiation** of [[Radical Reactions]] to begin. The vast majority of chemical reactions (especially those within organic chemistry) are **polar reactions** that involve *heterogenic bond formation* or *heterolytic bond cleavage* ### The Building Blocks of Reaction (Reaction Mechanisms) **Nucleophilic Attack** - Electrons are **always** the thing moving around within chemistry (except that nuclear radiation shit I think) - Nucleophiles are characterized by their lone pair of electrons, because these negatively charged electrons are trying to **Loss of a Leaving Group** - aaa **Proton Transfers** Hydrogen can be considered the key piece of nearly all organic reactions. Generally, when an atom (Ex: Oxide with two lone pairs) is protonated it will become far more reactive, making it much easier to alter any other bonds it may have. This is why many reactions (often "acid-catalyzed" reactions) begin by protonating the substrate to better induce a nucleophilic attack. **Rearrangements (Carbocations)**