Substitution Reactions

Substitution reactions is a functional group in specific chemical compound which replaced by another group such as an ion or atom. In the field of organic chemistry there are two types of substitution reactions like electrophilic and nucleophilic substitution which play significant role. Only deep understanding of a reaction type will let us predict the product outcome in a reaction. This is also favorable for optimizing a reaction with regard to variables like the temperature and selection of solvent. For example:

CH₄ + Cl₂  →  CH₃Cl  +  HCl

 Here is the substitution reaction of the photochemical chlorination of forming methyl chloride.

Determining the State: Reagents

Substitution reactions are classified into three common classes, depending on the type of atom or group that acts as the substituent. In one of them the substituent is electron-rich and offers the electron pair for bonding with the substrate, the molecule being transformed. This kind of reaction is called as nucleophilic substitution. A few examples nucleophilic reagents are the halogen anions, ammonia, the hydroxyl group, the alkoxy group, the cyano group, and the hydrosulfide group. A nucleophilic reacts with an aliphatic substrate in a nucleophile aliphatic substitution reaction.

Nucleophilic and Electrophilic Reactions

 These substitutions can be formed by two various mechanisms such as unimolecular nucleophilic substitution and bimolecular nucleophilic substitution. The first one has two steps where the leaving group departs, forming a carbocation. In the second, the nucleophilic reagent attacks the carbocation and forms a sigma bond. And the consequences can be either inversion or retention of configuration. Bimolecular nucleophilic substitution has just one step and is he attack of the reagent and the expulsions of the leaving group occur concurrently. This mechanism constantly results in inversion of configuration. When the substrate is an aromatic compound the reaction type is nucleophilic aromatic substitution.  Carboxylic acid derivatives react with nucleophiles in nucleophilic acyl substitution. This type for reaction can be useful in preparing compounds.

The second type electrophilic reaction is where the substituent is deficient in electrons, and the electron pair for bonding with the substrate comes from the substrate itself. Examples for this type of species are the hydronium ion, the hydrogen halides, the nitronium ion, and sulfur trioxide. Electrophilic reactions to other unsaturated compounds than arenes commonly direct to electrophilic addition rather than substitution.

And systematic names for substitution reactions are composed of the parts: name of group introduced + de + name of group replaced + action, with suitable elision or change of vowels for euphony. Hence, the replacement of bromine by a methoxy group is called methoxydebromination.

Questions:

• What is substitute reaction?
• List down some of the functions of substitute reaction.