Describe the differences between substitution and electrophilic substitution reactions.

Substitution and electrophilic substitution reactions differ in the type of reactants involved and the mechanism of the reaction.

Substitution reactions involve the replacement of an atom or group of atoms in a molecule with another atom or group of atoms. This occurs when a nucleophile attacks a molecule, displacing a leaving group. The nucleophile is a species with a lone pair of electrons, such as a halide ion or an alcohol. The leaving group is an atom or group of atoms that can depart with a pair of electrons, such as a halogen or a proton. Substitution reactions can be either unimolecular (SN1) or bimolecular (SN2), depending on the rate-determining step of the reaction.

Electrophilic substitution reactions involve the addition of an electrophile to a molecule, which then undergoes a rearrangement to form a new molecule. This occurs when an electrophile attacks a molecule, forming a carbocation intermediate. The electrophile is a species that is electron-deficient, such as a proton or a halogen. The carbocation intermediate is a positively charged species that can undergo rearrangement to form a new molecule. Electrophilic substitution reactions are common in aromatic compounds, where the electrophile attacks the ring and forms a new substituted aromatic compound.

In summary, substitution reactions involve the replacement of an atom or group of atoms in a molecule, while electrophilic substitution reactions involve the addition of an electrophile to a molecule, which then undergoes a rearrangement to form a new molecule.