  substitution reaction (also known as single displacement reaction or single replacement reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. substitution reactions are of prime importance in organic chemistry. substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved. there are other classifications as well that are mentioned below. organic substitution reactions are classified in several main organic reaction types depending on whether the reagent that brings about the substitution is considered an electrophile or a nucleophile, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical or whether the substrate is aliphatic or aromatic. detailed understanding of a reaction type helps to predict the product outcome in a reaction. it also is helpful for optimizing a reaction with regard to variables such as temperature and choice of solvent. a good example of a substitution reaction is halogenation. when chlorine gas (cl-cl) is irradiated, some of the molecules are split into two chlorine radicals (cl.) whose free electrons are strongly nucleophilic. one of them breaks a weak c-h covalent bond and grabs the liberated proton to form the electrically neutral h-cl. the other radical reforms a covalent bond with the ch3. to form ch3cl (methyl chloride). {| class="wikitable" |- align="center" || substitution reaction : chlorination of methane |- align="center" !chlorination of methane by chlorine |} ==nucleophilic substitution== in organic (and inorganic) chemistry, nucleophilic substitution is a fundamental class of reactions in which an electron deficient nucleophile selectively bonds with or attacks the positive or partially positive charge on an atom or a group of atoms. as it does so, it replaces a weaker nucleophile which then become a leaving group; the remaining positive or partially positive atom becomes an electrophile. the whole molecular entity of which the electrophile and the leaving group are part is usually called the substrate.[1][2] the most general form for the reaction may be given as where r-lg indicates the substrate. : nuc: + r-lg â r-nuc + lg: the electron pair (:) fro
Chemical_reactions Substitution_reactions