The order of basicity among the following compounds is:
A ) I > IV > III > II B ) II >I IV > III C ) IV > I > II > III D ) IV > II > III > i
Hint: Consider various factors such as number of amino groups and number of double bonds. Greater is the number of amino groups, greater is the basicity.
Complete step by step answer: In compound IV, three amino groups are present, whereas in all the remaining compounds, only two amino groups are present. Greater is the number of amino groups, greater is the basicity. Also, in compound IV, when a proton is accepted, the stabilisation of the positive charge in the conjugate acid involves resonance with two different amino groups. However, in case of compound I, this resonance is with only one amino group. Greater is the number of amino groups, greater is the number of resonance structures and greater is the delocalisation. Hence, compound IV is more basic than compound I.
In compound II, only one double bond is present whereas in compound III, two double bonds are present. Hence, the extent of delocalisation is greater in compound III than in compound II. Greater is the delocalisation, lesser is the availability of lone pairs of electrons for donation to suitable acid. Hence, II is more basic than compound III.
Hence, the option C ) is the correct answer.
Note: If the extent of delocalisation of electrons is greater, then lower is the basicity.