Which of the following compound exhibit highest basic character in aq…

Amines

Amines can be considered as derivatives of ammonia, obtained by replacement of one, two or all the three hydrogen atoms by alkyl and/or aryl groups. They are classified as primary (1°), secondary (2°) and tertiary (3°) depending upon the number of hydrogen atoms replaced by alkyl or aryl groups in ammonia molecule. In aryl amines, –NH₂ group is directly attached to the benzene ring. C₆H₅NH₂ is the simplest example of aryl amine. Amines can be prepared by various synthetic pathways. For example the reduction of nitro compounds with metals in acidic medium produces amines. Reduction with iron scrap and hydrochloric acid is preferred because FeCl₂ formed gets hydrolyzed to release hydrochloric acid during the reaction. Thus, only a small amount of hydrochloric acid is required to initiate the reaction.

Similarly, an alkyl or benzyl halide on reaction with an ethanolic solution of ammonia undergoes nucleophilic substitution reaction in which the halogen atom is replaced by an amino (–NH₂) group. The primary amine thus obtained behaves as a nucleophile and can further react with alkyl halide to form secondary and tertiary amines, and finally quaternary ammonium salt. Reduction of nitriles and amides also yield amines.

Moreover, amines behave as nucleophiles due to the presence of unshared electron pair. Amines, being basic in nature, react with acids to form salts. Basic character of amines can be better understood in terms of their K_b and pK_b values. Larger the value of K_b or smaller the value of pK_b, stronger is the base. Basicity of amines is related to their structure. Basic character of an amine depends upon the ease of formation of the cation by accepting a proton from the acid. The more stable the cation is relative to the amine, more basic is the amine.