Carbon–hydrogen bond activation or C-H activation is a reaction that breaks a carbon–hydrogen bond. Most times, the reaction involves organometallic complexes. The reaction path has coordination of a hydrocarbon to the inner-sphere of the metal atom (“M”). The reaction path includes either an intermediate “alkane or arene complex” or as a transition state leading to a "M-C" intermediate. The reaction path makes C-H activation different from other reactions. During the C-H breaking event the hydrocarbyl group remains linked in the inner-sphere and under the influence of the metal atom.