(i) Consideringthe inductive effect of alkyl groups, NH3, C2H5NH2, and(C2H5)2NH can be arranged in the increasing order of their basicstrengths as:
Again, C6H5NH2 hasproton acceptability less than NH3. Thus, we have:
Due to the −I effect of C6H5 group,the electron density on the N-atom in C6H5CH2NH2 islower than that on the N-atom in C2H5NH2, butmore than that in NH3. Therefore, the given compounds can be arranged in theorder of their basic strengths as:
(ii) Consideringthe inductive effect and the steric hindrance of the alkyl groups, C2H5NH2, (C2 H5)2NH2, and their basic strengths as follows:
Again, due to the −R effect of C6H5 group,the electron density on the N atom in C6H5 NH2 is lower than that on the N atom in C2H5NH2.Therefore, the basicity of C6H5NH2 islower than that of C2H5NH2. Hence, the given compounds can be arranged in theincreasing order of their basic strengths as follows:
(iii) Consideringthe inductive effect and the steric hindrance of alkyl groups, CH3NH2,(CH3)2NH, and (CH3)3Ncan be arranged in the increasing order of their basic strengths as:
In C6H5NH2, Nis directly attached to the benzene ring. Thus, the lone pair of electrons onthe N−atom is delocalized over the benzene ring. In C6H5CH2NH2, Nis not directly attached to the benzene ring. Thus, its lone pair is not delocalizedover the benzene ring. Therefore, the electrons on the N atom are more easilyavailable for protonation in C6H5CH2NH2 thanin C6H5NH2 i.e., C6H5CH2NH2 ismore basic than C6H5NH2.
Again, due to the −I effect of C6H5 group,the electron density on the N−atom in C6H5CH2NH2 islower than that on the N−atom in (CH3)3N.Therefore, (CH3)3N is more basic than C6H5CH2NH2.Thus, the given compounds can be arranged in the increasing order of theirbasic strengths as follows.
