The compound which is more basic have high value of Kb and a lower value of pKb (as Kb ).
In aryl amines the lone pair on N is in conjugation with the benzene ring making benzene ring as EWG and thus the lone pair on N will be less available for protonation. Hence, aryl amines are less basic and C6H5NH2 will be least basic.
In C6H5CH2NH2, benzene ring is not directly attached to N thus the lone pair on N will not be in conjugation with benzene ring electrons thereby increasing its basicity.
In C6H5CH2NHCH3 , benzene ring is not directly attached to N thus the lone pair on N will not be in conjugation with benzene ring electrons. Also, a methyl group is attached to N which will act as EDG which will further increase its basicity.
Order of Kb - C6H5NH2> C6H5CH2NH2 > C6H5CH2NHCH3
Order of pKb- C6H5CH2NHCH3 > C6H5CH2NH2 > C6H5NH2
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