(i) Elimination Reaction:
An elimination reaction involves the removal of two adjacent atoms or groups from a molecule to form a double bond or a triple bond. One common example is the dehydrohalogenation of alkyl halides. For instance, consider the reaction:
\(CH_3CH_2Br \rightarrow CH_2=CH_2 + HBr\)
In this reaction, ethyl bromide undergoes elimination to produce ethene and hydrogen bromide.
(ii) Electrophilic Substitution Reaction:
An electrophilic substitution reaction occurs when an atom or a group of atoms in a molecule is replaced by an electrophile (electron-seeking species). A classic example is the bromination of benzene:
\(C_6H_6 + Br_2 \rightarrow C_6H_5Br + HBr\)
In this reaction, one hydrogen atom in benzene is substituted by a bromine atom in the presence of a bromine molecule.
(iii) Nucleophilic Substitution Reaction:
A nucleophilic substitution reaction involves the replacement of an atom or a group of atoms in a molecule by a nucleophile (electron-rich species). Consider the reaction between an alkyl halide and a nucleophile, such as hydroxide ion:
\(CH_3CH_2Br + OH^- \rightarrow CH_3CH_2OH + Br^-\)
In this example, the bromine atom in ethyl bromide is replaced by the hydroxide ion, resulting in the formation of ethanol and bromide ion.
